The Science of Everything Podcast - Episode 150: How Home Appliances Work

Episode Date: December 31, 2024

An exploration into the exciting world of home appliances and devices. We begin with a journey through the kitchen, discussing the design and operating principles behind the refrigerator, rice cooker, convection oven, microwave, and dishwasher. We proceed to the laundry to examine how the washing machine, vacuum cleaner, clothes iron, and dryer work. Finally we take a bathroom break and consider how the flush toilet, sinks, and plumbing work.  If you enjoyed the podcast please consider supporting the show by making a PayPal donation or becoming a Patreon supporter. https://www.patreon.com/jamesfodor https://www.paypal.me/ScienceofEverything

listening to The Science of Everything podcast episode 150, how home appliances work. I'm your host, James Fodor. So to celebrate the milestone of 150 episodes of the podcast, I'm going to do something a little bit different, which if you've been long-term listeners, you may know, was actually an original intention of this podcast, which was to talk more about how stuff works. And we've done a little bit of that in the past. They did a series on how computers work for example. But in this episode what we're going to look at is a variety of other home appliances or I guess technologies more broadly. So we're going to focus on items you'd find in the kitchen, the laundry and the bathroom and just talk a bit about some of the engineering and science

behind them. Many of these devices aren't especially complicated, at least in general principles, much simpler than computers, for example, but nonetheless, I think they're quite interesting and it's been a enjoyable experience to read up and learn more about how they work. And one of the advantages of doing this episode now is I can appeal to some of the physics and chemistry principles that we've covered in previous episodes. Also, at the conclusion of the content, I'll talk a little bit more about the future of the show and some ideas I have going forward, so stay tuned for that. But without further ado, let's jump in and start going through the list of applying

and technologies that I have here, starting in the kitchen with, I think, probably the most interesting, one of the more interesting examples, which is the refrigerator. So a fridge is a home appliance which consists of a thermally insulated compartment and a heat pump. So the simple idea is that the heat pump transfers heat from inside the insulated compartment to the external environment, which cools the internal compartment below the room temperature. Fairly simple in principle. The technique behind it is interesting, so we'll go through that. Iceboxes have been used for centuries as a way to keep food cool, but the modern style of electric compression-based refrigerators for domestic use were only developed around the 1890s and 1900s and didn't really see widespread adoption until the 1920s. And if you look back at some of the

very earliest models, they look a bit funny, but it doesn't take long, you know, even in the 1930s and 40s, you see refrigerators look very much like at least cheaper models of refrigerators that you can buy today. So the fundamental technology hasn't changed that much in about a century. I should say that there are different types of refrigerators. What I'm going to be talking about is the most common style, which is compression refrigeration using electric power. So compression refrigeration relies on the fact that when a constant amount of gas is allowed to expand, it cools down. So this is something that I've talked about in past episodes, and it's the fundamental principle behind compression refrigerators. So when you compress gas, you exert a force on it, and that heats it up.

When you allow the gas to expand, that essentially uses energy, the gas uses energy to push out, and that reduces its temperature. Remember, temperature is proportional to the kinetic energy of the molecules, gas molecules in this case. So as those gas molecules effectively push outwards and expand, that uses up some of that kinetic energy, thereby cooling them down. So that's fundamentally where the sort of, quote-unquote, coolness comes from. It comes by allowing a gas to expand, but obviously there's more to it than that. So in most domestic refrigerators, a circulating refrigerant called R134A, which is a chemical designation for tetrafluoroethane, is used as the refrigerant. Tetrafluor ethane is basically just a fluorocarbone. The reason this is used, there's many different refrigerants that you could use,

but basically this is selected for most purposes because of a combination of desirable thermodynamic properties, as well as being relatively cheap and not too damaging for the environment. Previously, previous refrigerants that we used were responsible in no small part for the destruction of the ozone layer, and so they were replaced with more environmentally friendly chemicals. The way that the system works is that this refrigerant is stored in a closed loop, which think of it as essentially a series of pipe within the refrigerator. And the refrigerant is sealed within it, so it's not supposed to escape. If the refrigerant is allowed to escape in some form, generally you probably need to get a new refrigerator. And the circulation of the refrigerant through the series of pipes is what allows the fridge.

to stay cooler than its environment. So the refrigerant is passed through the sequence of pipes within the refrigerator, and it allows the internal compartment to stay cool by passing through a series of stages. So effectively, it's a cycle. So we'll start partway through and focus on the mechanism of cooling itself. So as I said, the mechanism of cooling is passing the refrigerant through what's called an expansion value, which allows it to dramatically expand in volume and thereby cools the refrigerator down or allows the refrigerant to cool. So the expansion valve is

basically a very, it's a very small valve that allows just a tiny amount of liquid refrigerant to pass through each time. So think of like a little tiny drop passing through which then expands dramatically and cools down and becomes a kind of a mixture of cold liquid and a low pressure gas. So there's a spring that regulates the amount of refrigerant that can pass through this small valve, which keeps it mostly tight but just allowing a little bit through each time. And there's a feedback mechanism that regulates the flow so that you get the right amount of liquid passing through depending on the temperature and other factors, right?

Now once the refrigerant has cooled down, this mixture of low pressure vapor and liquid then travels through another component called the evaporator, where it vaporizes completely as it accepts heat from the surroundings. So the evaporator is essentially a series of pipes which is connected to or in contact with the interior of the refrigerator. So this is how you essentially transfer heat from inside the fridge, from the internal compartment, to the refrigerant. That's the whole point, right? Cooling the refrigerant down itself won't cool the internal compartment of the fridge down unless you have some mechanism for exchanging heat between them. So this takes place in the evaporator.

So the refrigerant absorbs heat from the air inside the refrigerator internal compartment, thereby heating up slightly the refrigerant. I mean it's still fairly cold, but it heats up somewhat because of the energy that it's absorbing from inside, from the inside refrigerator compartment, and thereby causing it to vaporize completely. So at this point, we've passed the refrigerant through the expansion valve, which cools it down, and then we've exchanged, and then we've used that very cold. temperature of the refrigerant to accept some energy from the inside of the compartment

thereby cooling down the inside of the compartment. Now what we would like to happen next is for the refrigerant to cool back down again, right, so that it can accept more heat from the inside of the refrigerator compartment. Because obviously we want to keep using the refrigerant, we want to keep cooling down that internal compartment. The problem is that in order for it to cool back down, we need it to expand again. And we can't expand it again. we've already expanded it. We would need to first condense it down to a liquid and so that it can be

passed back through the expansion valve. In order for that to happen, we need to compress it first, right? So we've already allowed it to expand. We can't do that again without first compressing it back down again. So the refrigerant is passed to another component of the fridge called a compressor. And this compresses the refrigerant. So this exerts a force on the refrigerant, compressing it down from a relatively low pressure vapor to a high pressure vapor. Compression is performed by a mechanical device called a compressor, as I said, which is generally located at the bottom of the fridge. And in most fridges, the type used is called a scroll compressor, which consists of two interlocking spirals, so generally made of metal, so there'll be one sort of

fixed spiral that's affixed to the outside of the fitting. And then there'll be another interlocking spiral sort of inside there, the outer spiral. The spirals don't actually rotate with respect to each other. One is just sort of moved around with respect to the other. If you can kind of imagine two interlocking spirals and then imagine sort of rolling one around inside the other. The effect that that has is to gradually push the refrigerant in its vapor form from the outer part of the spiral to the inner part of the spiral. And what that does is it gradually pushes it into a smaller and smaller volume so that it becomes compressed. So this is the mechanism of the scroll compressor, it's basically just a way of physically pushing the

refrigerant into a smaller volume and thereby compressing it. So you're exerting a force on the refrigerant, reducing its volume, and that causes an increase in its temperature. So let's think about what's happened so far. We passed the refrigerant through an expansion valve, which cooled it down. We then absorbed some energy, absorbed some heat from the air inside the refrigerator compartment and then we compressed the refrigerant back down again into it into a smaller volume. The net result here is basically we've got back to where we started except the refrigerant has slightly increased in temperature. We reduce the temperature then absorbed some energy and then compressed it back

down again to increase temperature so the net result is a slight increase in temperature relative to where we started. In order for the cycle to be completed we we need to get back completely to where we started, which means we need to return the refrigerant completely to its initial state. So we can't have a build-up in energy in the refrigerant from as we turn around the cycle, because then eventually that will disrupt the process. So what needs to happen is that we need to dissipate this additional energy that the refrigerant has accumulated outside of the refrigerator.

So this is basically just an application of the second law of thermodynamics. In order to use energy to cool down the interior of the refrigerator, we need to dissipate heat outside the refrigerator. And that's what the condenser is for. So the condenser is a series of, essentially a series of pipes on the back of the refrigerator, where the vapor, that the compressed vapor of the refrigerant that's come out of the compressor, it's essentially exposed to the external air, the purpose of which is to dissipate heat to the outside. So this cools the refrigerant and allows it to condense back into a liquid. So remember when we compressed it using the compressor, it becomes a compressed and hotter, but it's still gaseous. It's, it

gaseous form. As it passes through the condenser, it cools down and condenses into a liquid and loses the extra energy that it picked up in the evaporator, which is where it, remember, picked up energy by cooling down the internal compartment of the refrigerator. And so after passing through the condenser, the now liquid refrigerant passes back through the expansion valve again, and then we repeat the process. So note that, as I said at the outset, the compression refrigerator relies on passing a refrigerant through a series of mostly pipes and components in a cyclical manner so that at the end of each cycle, the refrigerant is restored to its initial state, in terms of gaseous or liquid, pressure, density, temperature, and all of that. This process can be then repeated, you know, indefinitely,

as long as the refrigerator keeps operating. You don't have to add additional refrigerant. The overall result is that heat is transferred from the inside compartment of the fridge to the outside air via the medium of the refrigerant at the cost of a constant input of energy in the form of electricity. The electricity is used to operate the compressor. So the expansion valve does not actually use electricity. It might be the case that some of the more modern versions that have electronic sensors perhaps use some electricity, but you don't actually need that. And likewise, the evaporator and the condenser also don't use electricity.

is only needed for the compressor because you need to physically push the gas into a smaller volume that takes energy. So that's where the input of energy is. All of the other processes are effectively passive so they don't require energy and the refrigerant, as I said, is sealed off, separated from the internal and external compartments. And the heat transfer occurs via conduction in the evaporator and the condenser as well as thermal expansion as you pass the refrigerant. through the expansion valve. Freesers work in essentially exactly the same way as refrigerators. They just have a lower internal temperature. So fridges typically have an internal temperature of about four degrees, four degrees Celsius that is, whereas freezers are typically set to about

minus 18 degrees. Also interestingly, air conditions typically work in more or less the same way as a refrigerator as well. Obviously the design is somewhat different but the principle is very much the same. It's just effectively that you are inside of the internal compartment that's being cooled down. All right, so let's now move on from the refrigerator and talk about some other items that we might expect to see in the kitchen. And one that is a particular interest to me is the rice cooker. Rice cookers are very simple. Again, you can buy more expensive ones that may have electronic control circuitry, but fundamentally, rice cookers really don't need many complicated components at all. So a rice cooker or rice steamer is an automated kitchen appliance designed

specifically to steam rice and the first modern electric rice cooker was developed by Mitsubishi Electric in 1923 and it's pretty much the same in concept and overall design to today's automatic electric rice cookers. So all it really consists of is a metal bowl that you fill with rice and water. So as electricity is typically used to heat the bowl, that then calls. That then causes the water to increase in temperature and eventually reaches boiling point, so 100 degrees Celsius. The energy that you continue to add then no longer increases the temperature of the water, this is the principle that we've discussed in again in previous episodes. As you continue to add energy to a boiling liquid, that energy goes into converting the water into a vapor form

and not into increasing the temperature of the liquid. So the temperature of the bowl will never exceed 100 degrees Celsius as long as there is water still to boil. Once all the water has been absorbed by the rice, that means there's no more water to boil and the temperature of the bowl can then rise above boiling point is no longer in contact with the water, which keeps it at 100 degrees. So the bowl then increases in temperature ever so slightly above the 100 degree cutoff point. That once a cut off temperature is reached called the thermostat cutoff temperature, That trips the thermostat and then cuts off the power to the device, and so it stops heating. So that's effectively how it sort of knows, quote-unquote, that your rice is finished.

It doesn't actually know that your rice is cooked, all it knows, so to speak, is that all of the water has been boiled off. And so it's up to you to put in the right amount of water, of course. So there's many ways of implementing a thermostat. The simplest way is using what's called a bimetallic strip. I believe I've discussed these before. These rely on the fact that metals change in length when they are heated, And a very simple way to implement this is basically to construct a spiral of metals. So basically imagine having a straight rod of one metal on one side, like, say, steel and then a different metal on the other side, like copper, for example, so steel and copper.

And then imagine just winding so that it forms a spiral. So you've got this spiral of metal. On one side is steel on the other side is copper or some other metal. If you anchor the center of the spiral to a fixed point, what will actually happen is that the entire spiral will rotate as its temperature changes, essentially because the outer and inner parts of the spiral being made of different metals will expand and contract at different rates, and that effectively results in a rotation of the entire spiral, again, if it's anchored at a central point. And so you can just literally then attach that to a switch, so it can actually physically move the switch. Of course there are other ways to do that, but you can actually just use a biometallic strip to physically rotate and turn on and off. Once it passes a certain temperature, it'll flick off the switch and you turn off the power to the device. Of course, the energy for boiling the water as well as the energy to physically turn on and off the switch comes from the electricity that you're passing into the device.

Rice cookers are really cool. I think they're very useful for cooking, and they're very cool as a simple device that allows us to understand a number of and apply a number of important physical and chemical principles, particularly the idea about boiling points and where the energy is going and bi-metallic strips. All right, let's move to a different type of cooking device, a convection oven. So an oven is a very simple device. Really all it is is a thermally insulated box and some method for heating it. So the earliest ovens date back to about 30,000 BC in Central Europe and have been found in many parts of the world even before agriculture began. So the oldest type of ovens were basically just pit. So these are

called earth ovens or earthen ovens. It's a pit dug into the ground, which you then heat with rocks or smoldering debris. More recent than that, and a step up are clay ovens. So a clay oven is constructed like a truncated cone, so it usually has an opening either at the top or sometimes at the bottom, which you can use to stoke the fire. So it's fundamentally quite similar to an earth oven, except instead of digging a hole and putting the hot stones or the fire in, you put those on the surface of the ground and then build a dome above it. It tends to give a bit better heat insulation and more control over what you're doing. Clay ovens have also been built for thousands of years. A more recent design, again, is a masonry or brick oven. And these are still used. Some people

prefer them for various reasons. A masonry or brick oven essentially consists of a baking chamber which is made of brick, concrete or stone, and then you often hit it using wood or coal. Gas ovens were developed in the early 19th century, and these are typically made of metal. With a gas pipe at the bottom, you like the gas pipe, and that provides a source of heat, which you then use to heat up the oven. And so those gas ovens are a direct ancestor of modern electric ovens, which are pretty much just the same as a gas oven, but instead of gas pipes, you have electric heating elements, which convert electrical energy into heat energy,

basically through electrical resistance. And this is a principle that's used in a number of other electrical devices that produce heat. It's basically utilizing the fact that if you pass an electrical current through a metal, there'll always be some amount of resistance. So if you choose the type of metal and the design appropriately, you can actually utilize this to produce a lot of heat. Usually in a lot of electric devices, you actually don't want that. The heat loss is an undesirable buy product and the potential fire hazard. But in the case of heating elements in an oven, that's exactly what you want. And so these electrically resistive heating elements are just used to get up to a very high temperature, and then they heat up the air through conduction. And they can

sometimes be assisted by a fan. So fan-forced ovens will have a fan at the back that basically pushes the air around, help to circulate it, help to get a more even heat, and produce some convection forces as well that help to circulate the air and improve the flow of heat. But that's basically all it is. An oven is fundamentally just a thermally insulated box and a wave heating it up. Moving on now to a bit more of a modern type of cooking apparatus, the microwave or microwave ovens, as they used to be called. A microwave is an electric oven that heats and cooks food by exposing it to electromagnetic radiation, specifically in the microwave frequency range. This is a completely different mechanism to what is used in traditional ovens or convection ovens. I'm calling them here just to contrast them.

So a traditional oven heats and cooks food by essentially placing that food in a thermally insulated box, heating up the air inside that box to a very high temperature, hundreds of degrees, and then exposing it to that temperature for enough time for the food to heat up and various chemical reactions to occur. The point is that the fundamental mechanism of cooking in a traditional oven is just to heat up the air and weight essentially, heat up the air inside the oven and wait. Microwaves work completely differently to that. So microwaves will not really heat up the air inside them at all. I mean, I guess they do a little bit because there'll be some conduction of energy from the

food and the container to the air inside. But basically, microwaves don't heat up the air inside them. They only heat up the food and the container that it's in. Microwave ovens are relatively new. So the first cooking of foods used. using electromagnetic radiation from a shortwave radio transmitter was demonstrated in 1933 at the Chicago World's Fair. This principle was developed to produce the first microwave that was commercially available

in 1947, which was actually much earlier than I realized, but microwaves didn't become widely used until the 1970s. A microwave oven generally consists of a high voltage DC power source, a device called a cavity magnetron, which is what produces the microwaves themselves, a control circuit, a short wave guide and a turntable. Well, the turn table is the platform that usually rotates that you place your food on. Rotation is just to help improve the evenness of the cooking, so that part's fairly straightforward. The power supply is used to convert the alternating current that's provided by the outlets in, you know, in most residential homes, into a direct current,

so DC current, which is used in internally, in actually, well, the microwave and most other domestic appliances as well internally use DC current. And here it's particularly important because the power supply is connected to a device called a magnetron. The magnetron, or a cavity magnetron specifically, there's different types of magnetons, the cavity magnetron is a device that converts DC electric current into microwaves. Essentially this happens by interacting the electrons from the current, so a DC power supply will produce a steady flow of electrons. You interact these electrons in a certain way with a magnetic field, and that can produce electromagnetic radiation.

I'm not going to go into the physics of exactly how that happens, just because it would take a little bit too long and be a bit hard to explain here. But we do know from episodes in the past that accelerating electrons emit electromagnetic radiation, and so you just need to accelerate the electrons in the right way, in the right context, in order to emit electromagnetic radiation of the right. right frequency in the microwave range. The other component that I mentioned is the wave guide. A wave guide is a structure that, well, it guides waves, specifically electromagnetic waves, by restricting the transmission of energy to one direction or other. Usually they consist of a

hollow metal, basically because an electromagnetic wave can't travel through metal, because it's a conductor, electromagnetic fields can't exist inside conductors, and so microwaves can only be propagated through the air inside the central hollow section of the pipe. You can think of a wave guide as basically like a wire that transmits electromagnetic radiation. So just as a wire is used to transmit electric current, a waveguide is used to transmit electromagnetic radiation. This may seem a bit strange the idea that we use a hollow tube to transmit electromagnetic radiation. But remember, electromagnetic radiation just consists of a series of fluctuations in electromagnetic fields. Electromagnetic fields can't exist inside a conductor, so you don't use a wire to do this, you can just use air.

And the key thing is that a wave guide needs to be constructed to match the size of the wavelength of the electromagnetic waves that you're interested in. Microwaves have a wavelength of about 12 centimeters, so you need to have a wave guide that's appropriately sized to allow that to propagate. So, to summarize, the power supply converts your AC to DC power, which produces a steady stream of electrons. The magnetron then uses this steady stream of electrons with an electromagnet to convert, to produce electromagnetic radiation in the microwave range. The waveguide then directs this electromagnetic radiation into the internal cavity, where it is emitted and bounces around off the air. sides, bottom and top of the internal compartment because they're coated with a reflective metal. And the point is that as these microwaves bounce around the internal compartment, they repeatedly pass through the food and are gradually absorbed. The way that food absorbs the

electromagnetic radiation is quite interesting. So we've talked about many of the components here before in previous episodes. The microwave radiation, or technically it's the energy contained in the microwave radiation is absorbed by polar molecules, which are molecules that have an electric dipole moment. So water is a very good example. Water is a polar molecule because at one sort of end of the molecule, there's the oxygen. At the other two ends there are the two hydrogen atoms. The oxygen has a higher electronegativity than the hydrogens, so it kind of pulls the electrons more towards its side, which means that the water molecule has a relatively more negative side and a relatively more positive side. So it's a dipole. It's a polar molecule. And there are many other

molecules like this as well. Water is just a good example. Now, when you place a polar molecule, a molecule with an electrode dipole inside an electromagnetic field, it tends to align with that electromagnetic field, which makes sense because charges are affected by electromagnetic field, so there's sort of nothing surprising there. If you constantly flip the direction of that electromagnetic field, then the molecules will flip in the direction. So they'll go from like, pointing up to pointing down, pointing up to pointing down, they'll flip back and forth as you oscillate the direction of the field. So this is what happens when you pass electromagnetic radiation through the food. Electromagnetic radiation is just oscillations in an electromagnetic field.

And so what's happening is that as the radiation passes through, the field is oscillating. It's going up and down, back and forth, so to speak. And so the polar molecules, molecules with electric dipole inside the food, will be constantly rotating. Essentially, they're flipping from being oriented up to being oriented down, to being up to down, and so forth. Now, as these molecules constantly rotate rapidly back and forth, they sort of push, pull, collide, and bump into other molecules that are surrounding them because of the electrical forces connecting these molecules together. And this distributes the energy from the rotating molecules to adjacent molecules and atoms in the material.

Temperature, as we've said, is directly related to the average kinetic energy of the atoms in a material. And so as the dipole molecules are rotating, they're colliding, pushing, bumping into surrounding molecules, this trans-sum of this energy is thereby converted into kinetic energy of the surrounding molecules, thereby heating up the food. Now, there's a bit of an urban legend that there's something special about the frequency of microwave radiation that means that it increases the temperature of water or something like that. It's not really accurate. What is true is that water is a polar molecule,

and polar molecules have an electrical dipole, which is affected by microwave radiation. But water is not special in that. It's not the only molecule that has an electric dipole. Alcohol, for example, ethanol also has an electric dipole, and so will be heated in a similar way. So different molecules will be affected in slightly different ways, because each has slightly different electrical properties.

But speaking generally, any molecule with an electric dipole, will be heated up in a similar way if you put it in a microwave. And then other molecules that don't have an electric dipole are heated up through this process of bumpage and collision, which dissipates the energy out, and thereby warms up the entirety of the food or dish that you've placed there. What a microwave does is effectively it converts the electrical power into electromagnetic radiation in the microwave range, which in turn is converted into the internal kinetic energy of molecules in the food. This is actually a much more efficient heating mechanism than traditional ovens, which first have to heat up the air, which takes a lot of energy.

So they first have to heat up the air inside the oven, and only then do they actually heat up the food. So there's much more of a loss in that process, whereas microwaves are much more direct to that magnetons can very effectively convert electrical energy into electromagnetic radiation, and then that is absorbed directly by the food to heat it up. So they're much more energy efficient than traditional ovens. Another point about microwaves is their safety. So when they were introduced and still sometimes to the present day, people express a concern that microwaves use radiation and radiation is harmful. So microwaves can be dangerous, mostly if you use them improperly, basically because they can heat up objects to a significant degree, but of course conventional ovens are like that as well.

With regard to the radiation itself, first of all, microwave radiation is non-ionizing radiation. So it can warm up material, but it can't cause the type of damage that many people worry about, that radiation can cause only much higher frequency radiation. It can cause the sorts of damage that people worry about in terms of cancer and radiation sickness and things like that. Microwave radiation is far too long wavelength for that. It doesn't have nearly enough energy to cause ionizing, it to cause ionization of tissue. The other reason not to be worried is that the mesh doors of microwaves, and also surrounding the rest of the internal compartment,

are covered with a reflective metallic material, and this effectively acts as a Faraday cage. So the perforations in the mesh door are much smaller than the wavelength of the microwaves, which means they can't get through. Remember that microwaves are fluctuations in electromagnetic fields. Electromagnetic fields cannot exist inside a conductor, and so if you have a conductor with mesh or with holes in it,

where the holes are smaller, than the wavelength of the electromagnetic waves in question, then those electromagnetic waves cannot pass through that conductor. That's how Faraday cage's work. Visible light can pass through, because visible light has a much, much smaller wavelength, but the microwave radiation that's actually heating up the food cannot pass through. So there really shouldn't be any leakage from inside the microwave to the outside, if it's properly sealed. If there is such leakage, you should probably consider getting a new microwave. Another interesting phenomena of microwaves is that the The microwave radiation can't actually penetrate more than one or two centimeters into the food.

So typically what happens is that only the outer sort of skin of the food, the first couple of centimeters, is cooked directly, is heated directly by the waves themselves. The interior of the food will be cooked by conduction. So it heats up by conduction due to direct thermal contact with the outer layers. This relates to another myth of microwaves, which is that food is somehow cooked from the inside out. And that just isn't true. So in a conventional oven, the food is heated through conduction, so direct contact between the air, which is heated, which is hot, and then the food itself. In a microwave, that's not the case.

However, it's still the case that the electromagnetic radiation, the microwaves, need to pass through the food. And they need to pass through the outer layers before they can get into the center of the food. And, of course, they'll be absorbed by the outer layers before they get to the center layers of the food. So the general principle is still the same that the outer layers are going to get cooked before. the inner layers. Now, sometimes it can be a bit more complicated than that. If the food has an irregular consistency, then certain parts are more watery or less watery than others or something like that. They may cook faster or slower because the material that it's made of does matter. Again, speaking generally, the outer layers will heat before the inner ones. It's also a reason why

it's important and helpful to stir the food in the microwave just to help it cook a bit more evenly. And you can't assume that the food will have cooked entirely evenly as well, because again, due to inconsistencies in the constituencies of the food, some regions of it may heat up quicker than others. Now, I mentioned before that I'm not really going to talk too much about the chemical reactions involved in cooking today, but I will just mention that microwave ovens do cook food, but they don't cook it in the same way as conventional ovens. In particular, they don't directly brown or caramelize the food. This is why you don't really bake in a microwave oven, for example, because they don't really produce the temperatures necessary for meilard reactions to

occur. So these are a type of chemical reactions between sugars and amino acids that produces browning of food like cookies or meat or potato fries, things like that. So this type of cooking where you think of browning something in the oven, you know, involved in baking or roasting and things like this, you can't really do that in a microwave. again because it just doesn't reach the required temperatures. Maybe there's some workaround to this, but in general, that sort of cooking isn't used for microwaves. And that's why a lot of people actually just use them for reheating food, which is what they're very good at. But they can be used to cook food as long as you don't need those particular types of reactions to occur.

All right. Now let's move on to talk about another appliance in the kitchen, and that is the dishwasher. A motorpowered dishwasher was developed in the 1880s, which, if you look it up, it's very interesting. it's sort of hand-cranked. But an electric dishwasher was first marketed by General Electric in the 1920s. So about as old as an electric refrigerator. So a dishwasher cleans dishes fairly simply, really, by spraying hot water at them, hot water mixed with a special detergent.

And, of course, you need to stack the dishes in a certain way on racks so that the hot water can access them. But fundamentally, that's really all that's happening. Electric dishwashers typically have two spray arms, so one at the top and one at the bottom. can see them if you look in, the bottom one's typically easier to see, unless you want to stick your head right in and look up, which might be interesting. What happens is that the soapy water is passed through the spray arms, and that the pressure of the water causes them to spin around, kind of like garden sprinklers. As the arm rotate, the water is pushed out of the small holes in the upper and lower surfaces.

and so what you get is just a series of hot spinning jets of water that fire up and down and clean off your dirty dishes. The water is heated to about 75 degrees, so that's enough to kill most bacteria, but not all of them. It's not a full sterilization, but it should significantly reduce the amount of bacteria on your dishes. And of course, there's a series of cycles that the dishwasher goes through to wash and then rinse and then dry the dishes. That's obviously quite specific to the particular model that you have. But there's not really too much more to say about that. Fairly simple device. Now we're going to move from the kitchen to the laundry,

and I guess we're on the theme of cleaning. So there's going to be a few more cleaning devices here. And the next thing we'll talk about is the washing machine. So the first electric washing machines were introduced in 1900s. Once again, there were mechanical washing machines that existed well back into the mid-19th century, which again often involved putting the dishes in a tub and sort of whining, a crank which would move them around. The first modern-style washing machines with a fully enclosed design appeared in the 1930s. So again, approximately 100 years ago, we're seeing a theme here.

Many of these modern devices were introduced in their modern form in the 1920s or 1930s. Electric washing machines consist of two drums, one of which is located inside the other. So the inner drum is the one you see when you open the door or the lid of the washing machine. There's two common designs of washing machines, front loading and top loading washing machines. Top loading washing machines are more common in the US, while front loading designs are more common elsewhere. So henceforth, I'm going to be talking about the front loading washing machine, although the design of top loaders is in principle the same. It's just there's some details that are different because of the different orientation. So in a front loading design, the drum faces forward.

The idea is you put your clothes inside the door from the front, and the whole drum then the inner drum rotates around a horizontal axis, kind of like a car wheel. The drum has lots of small holes in it, which you can see if you look at it, which allow the water to come in, and it also has sort of indented paddles around the edge, which helped to slosh the clothes around and the water around. So that inner drum that rotates around and pushes the clothes around is located inside a second larger drum, that is usually not visible. You shouldn't see it if your washing machine is working properly. The purpose of this outer drum is to hold the water inside the inner drum. The inner drum, as we said, has perforations, it has holes in it, so it's not watertight. The outer drum is watertight. Water is added to the inner drum by pipes, so obviously you connect your washing machine to the plumbing, which will supply the water, and you also need to collect it to an electrical

power socket, which supplies the energy that's needed to power the motor, which rotates, the inner drum. What actually cleans the clothes is a combination of the detergent, which you obviously insert as well, which is then mixed with the water. The moistening of the clothes then help the detergent to access all parts of the clothes and to gain access to the fabric. And really, the cleaning is done by the repeated mechanical motion of the water mixed with the detergent as the inner drum continually rotates backwards and forwards and paddles push your clothes around. It also helps to push water and detergent solution through the clothes load. So it passes the water through.

The water will get dirty as it absorbs dirt from your clothes. So then it will drain off the dirty water and add new water and it keeps going. The process is surprisingly motion intensive, which you would be aware of if you are familiar with how people used to have to wash clothes, which was by essentially repeatedly rubbing them against a metal board with soap. It really does require a lot of physical motion to actually sort of force the dirt out of the fabric, to push it out of the fabric. And so washing machines really do, even more than many other devices that we have in our homes today, they really do save a lot of hard physical work. We should be grateful for that.

All right. The next device we'll talk about is the vacuum cleaner. So electric vacuum cleaners were first introduced in the 1900s, though they didn't become widespread until after World War II, so around the 1950s. Of course, we all know that a vacuum cleaner sucks up air and dust and debris with that air. The suction is caused by a difference in air pressure, which essentially is just produced by a fan. Obviously, it's a special type of fan designed for this particular purpose. The fan is driven by an electric motor, and the fan pushes air out the back. That reduces pressure inside the machine, which then results in, effectively, a suction effect,

as air is pushed by atmospheric pressure through the nozzle and into the vacuum device. So although we think of the machine sucking up the machine sucking up the, air. It's perhaps more accurate to think of the air and the dust being pushed into the bag by the atmosphere. Or to put it another way, vacuum clears would not work in a vacuum, somewhat ironically. Dirt is also removed by the vibration of the nozzle, owing to the motor that turns the fan, and the mechanical action of the brush will also help to dislodge dirt. So at this point, I think I thought it might be interesting also to talk briefly about how fans work. That might not seem like a very interesting question. Well, we know how a fan works. It's attached to a motor which spins around

and that rotates the blades, which then push the air. But something that I'd never even really thought about until producing this episode is exactly how do fan blades push the air? How does a spinning blade actually push the air in one direction, but not the other? And the answer isn't too complicated, but it does require a bit of thinking through. So this type of fan is called an axial flow fan and the blades are, as you will see if you have a look at any fan, they're shaped in a particular way. And this is crucial. The shape of the fan is really what allows them to push the air in one direction. In particular, they push the air in a direction that is parallel to the axis around which the blades rotate. So you've got your central axis, blades rotate around that.

That central axis is parallel to the direction in which the air is pushed. The fan blades, as I said, are angled and shaped so that when air particles hit them, roughly head on, they are deflected in a direction away from the fan face parallel to that axis of rotation. So in other words, the shape of the fan blades and their orientation is what ensures that when air molecules hit them, those air molecules are directed in the design direction, parallel to the axis of rotation. How do we ensure that air molecules hit the blades in the right orientation? Well, that's what the rotation is. while the rotation is constantly moving the blades. In fact, it's probably better to think of the blade hitting the air rather than the air molecule rather than the other way around, because the air

was not stationary, but it's not moving as fast as the blade. So what's actually happening in just in front of the blades of the fan is that the air molecules are being pushed out quite rapidly, and this creates a slight pressure difference, a small low pressure zone just behind the fan, as the air is being pushed out quickly in front of the fan, there's a small low pressure zone just behind the fan. Air is then pushed into that low pressure zone by atmospheric pressure. So you will feel if you put your hand behind it an actual flow fan, there is a, there is a flow of air behind it as the air is being pushed into that low pressure zone. But the difference is that the air comes from all around, all around from behind above, below and sort of the whole

hemisphere on the back side of the fan. Air molecules are slowly, like relatively slowly compared to the front of the fan. They're relatively slowly pushed in, uh, towards that low pressure zone, and eventually they're pushed into just sort of in front of the fan, where the spinning blades then impart a force to them, which pushes them with a much rapid, with a much faster velocity forwards, and that's where you feel the air being pushed in front of the fan. Now, if you think about this, the volume of flow of air must be the same behind and in front of the fan. Otherwise, the fan would essentially be sucking up air from one side of the room to the other, which is not what happens, right? That the air has to come from some.

So given that, the reason why the air is moving much faster in front of the fan blade compared to behind it is essentially because the air is coming from a much broader range of locations. And so the velocity can be much slower. Whereas in front of the fan, the air is all pushed in the same direction. So the velocity is much faster. And this directly relates to principles of fluid dynamics, which we've talked about in the past, including the Bernoulli principle and other similar ideas. It's basically the same principle as if you have a hose and the water is coming out at a certain rate, and then you put your thumb partially covering the external nozzle, and the water now comes out at a much high velocity. That's effectively the same principle.

So by spinning these blades with the blades having the right shape, that allows the blades to constantly push air molecules on average in the forward direction. Not every molecule is strikes in the right. orientation, but in general, the blades are shaped so that they push most of the air molecules forwards. That constant motion can be kept up because of the rotation of the fan blades. They're constantly hitting new air molecules and pushing them forwards. That creates a slight low pressure zone behind the fan blades, where then the air is replaced by atmospheric pressure pushing air molecules from all around the back half of the fan into

to fill the gap. And so this simple device of an axial flow fan is basically all that's needed to produce a vacuum cleaner. Obviously, you do need to have a low pressure zone, in this case, in the front of the vacuum cleaner, which is produced by the axial flow fan, pushing the air out the back, and you need the nozzle to connect to that. But yeah, it's basically just a fan with a nozzle connected to it and a bucket to collect the dust. All right. And moving on now from vacuum cleaner to another, it's not exactly a cleaning appliance, but it's closely related. And that's the clothes ion. Clothes ions themselves are extremely simple. A clothes ion is just a device that you heat up and it presses clothes to remove wrinkles and creases. What's interesting about them is actually the chemistry behind how the creases and wrinkles are removed rather than the actual device itself. So people have used ions for a long time. Really, you can, just use any device that has a flat metal base and that you can heat in some way. So older

ions basically just consist of a heavy hunk of metal with a flat side that you can either place onto the fire to heat it up or you can put hot colds into it in order to keep it warm. Modern electric ions have a thermostat built into them, which is a significant improvement over early designs, which ensures that the temperature of the iron doesn't continually increase. And the basic idea is similar to other electric heating elements like an oven that you just use electric resistors to heat them up. And you use a thermostat to ensure that the temperature doesn't exceed a certain level. These types of electric ions with the thermostat were developed in the 1920s. The hot plate of the clozine is typically made of aluminium or stainless steel. It's polished

so that it's as smooth as possible, so you get the smoothest finished on the clothes as possible. Now, as I said, the interesting part of closines is how the actual ironing process in terms of the fabrics works. So plant-based fabrics, such as cotton, are predominantly made of the polymer cellulose. That's basically what plants are predominantly made out of. Cellulose chains in the fabric are connected together through a complex network of hydrogen bonds. This is a type of intermolecular bonding that we've talked about previously. And these hydrogen bonds help hold them together and kind of keep the chains connected. They hold the fabric together. Well, there's other ways the threads in the fabric are also threaded together so that the fabric is a whole stays together.

but talking about within each individual thread of the fabric, the hydrogen bonds hold the cellulose molecules together. Now, when you wash clothes, what happens is that the water breaks up the hydrogen bonding network. Cellulose chain's got a slide relative to each other, and when the clothes dry, the hydrogen bond network reforms, which causes the fabric to hold its new position. And generally, that new position will be sort of wrinkled. Basically because when you wash the clothes, they're kind of wrinkled up,

And when you dry them, you typically stretch them out to dry them, hang them on a clothesline or something. Or you could use a dryer, I suppose. That's another way to dry them. But either way, what you're not going to do is press them out carefully so that the hydrogen bonding network reforms in a way that the fabric is nice and smooth. So either way, there's going to be imperfections and little wrinkles and creases in the fabric. In order to remove those, what you have to do is heat the clothes. up again so that the hydrogen bonding network is disrupted, but then allow it to cool with the hydrogen bonding network reformed in a way that allows the, or is consistent with the fabric being flat. So that's what an iron does. It just heats up the clothes again. Often you wet them

a little bit as well, but you heat them up. By squashing it flat, you force the hydrogen bonding network into the way that you want it, consistent with the clothes being flat. And then when it cools, and when it cools down it will retain that shape, until you start wrinkling it again, of course. So the heat, the moisture and the pressure of the iron all help to break up the network and force the cellulose chains to sort of lie straight and flat. Moving on to the next item in our laundry. I want to briefly talk about the clothes dryer, or a tumble dryer, as they're also called. These are, again, fairly simple devices like a washing machine, except they don't use water. They just use air.

So tumble dry is continually drawing ambient air, heat it up, and pass it into the tumbler. Then they tumble the clothes around using an electric motor connected to a belt, which then rotates the internal drum. The blasting hot air and the tumbling motion helps to remove the water, just like drying clothes in a breeze. And at the end of it, you get nice, warm, dry clothes. Now because the water needs to be heated up and some of it's actually vaporized, this takes a lot of energy. You also need to run the motor that rotates the belt, but the heating up of the air and the water is what uses most of the energy. So this is why dryers are quite expensive to operate because of all that heating that's necessary. As an example of that, so physicist David McKay weighed his laundry before and after drying,

and he found that a typical load of four kilograms of dry washing emerged from the washing machine weighing 6.2 kilograms, so about 50% heavier. And that's even after the washing machine has vigorously spun the wet clothes to already remove a lot of water out of it. So the point is that freshly washed clothes absorb a lot of water. And that water has to all be removed in order to dry them. And that takes energy. So you can use the energy of the wind and the sun to remove all of that moisture. But if you want to do it faster using a clothes dryer, then you basically need to use a lot of electricity to heat up enough.

to evaporate or otherwise remove that water. Let's now conclude by talking about a couple of other ingenious mechanisms that have been developed to make our bathroom experience more pleasant. And we'll start by talking about perhaps the most important component in the bathroom, which is the toilet, a flush toilet. So a flush toilet disposes of human waste by collecting it in a bowl and then using the force of water to channel it out down a drain pipe, which then moves it through a sewer system, just another location for treatment.

I think it would be interesting to do a whole other episode on the sewage system because it's very interesting and something that often people, I guess we don't talk about very much. But here we're just going to focus on the toilet mechanism itself. Now flush toilets have been used for thousands of years. The ancient Romans used them, for example, but obviously they didn't have the same mechanism that we currently use. The Roman flush toilet was basically a continual stream of water, pushed away the waste. but the modern flush toilet featuring the development of the S-Trap, which I'll explain a little bit later, was invented by Scottish mechanic Alexander Cumming in 1775. You may have heard that an individual by the name of Thomas Crapper invented the flush toilet,

which people find him using because of his name. And honestly, that's almost true. So he didn't invent the first flush toilet, as I said, that was much earlier in 1775. Modern enclosed flush toilet designs were developed. around the mid-19th century. In 1880, so a little bit after that, Thomas Crapper introduced a new variation of the, essentially the piping system that carries away the waste, called the U-trap design, which is an improvement over the earlier S-trap. I'll explain the difference between these a little bit later. So Thomas Crapper did effectively invent an improved version of the flush toilet. He

didn't literally invent the flush toilet because it did exist before then, but he did introduce this was a substantial improvement. So there you go. Because there are several different variants of flush toilets, here I'm just going to focus on one of them. And specifically, I'll describe a system that uses a flapper flush valve with a ballcock mechanism. So in order to function, the flush toilet tank or the cistern, so that's the rectangular box at the top part of the toilet, the cistern needs to do three things. It needs to store water and then release it into the bowl when needed, and only when needed. So when you flush it. It needs to start refilling the water into the cistern after the flush is completed.

And thirdly, it needs to stop refilling once the cistern has been refilled. So it needs to basically store water until the water is needed. It needs to refill that water once the flush is done, and it needs to stop refilling at the right time. So again, you could imagine using a computerized system that has water sensors and things like that. But flush toilets were developed long before any of those existed, and in fact, flush toilets typically don't need electricity at all. they're a mechanical device and so you might ask well how does it know when to start filling up and then when the water level has as a reach the desired height and so forth well i'll explain how that works so flushing is fairly simple process you simply pull a lever or push a button that's linked

via a chain to the flapper valve which is then physically pulled out of the valve seat which allows the water to escape into the bowl so you pretty much just literally lifting up a flap which then allows the water to pass through the hole. The lifting is just indirect because you push a button or pull the lever. So that part's pretty easy. So all of the water in the cistern will then escape into the bowl and push out the contents. We'll explain that a little bit more detail in a moment. Once the cistern is empty, the flapper valve will fall back into place and it seals the cistern once again. But now we need to refill the cistern ready for the next flush. So this uses the mechanism that I'm describing here is a ballcock mechanism. So the ballcock is a floating plastic ball. I think

originally they were rubber. Obviously they didn't have plastic in the 19th century. But these days, the ballcock is a floating plastic ball, which is connected to a lever. And so it's made lighter than water so that it can float. This means that when the water level drops, as the water is escaping into the bowl, the ballcock descends, so it falls with the water because it's floating on top of it. And because the balk is connected to a lever, the lever sort of progressively rotates. You can imagine it starts off sort of flat and then it rotates, the arm rotates down and down as the balkok is falling with the lower water level, right? And you might see where this is going. So this lever that the balk is connected to, when it reaches a certain angle,

eventually that will open a valve, which allows more water to enter. So it's a very simple mechanism, right? The water level is connected directly to a valve, which when the water level is low enough, will open, allowing more water to enter and fill up the cistern. That connection between water level and opening the valve is made via the balkock, which it just falls down with the water level, rotating the lever, and opening the valve. And the reverse process also happens to shut off the inflow of water. So as the water level rises, the balk rises back up. Eventually it reaches a point where the lever passes a certain angle that shuts off the inflow of water

and now the cistern has been refilled. And just to add a little detail here, so obviously the ballcock mechanism needs to open the valve when the cistern is empty, well, close to being empty after a flush. But you don't want to close that valve immediately as the cistern starts filling again. It needs to fill right back up to full. So this is modulated by the water pressure. So the toilet is connected to water mains, which is pressurized. So once the valve is open, allowing the water into the cistern, the pressure sort of keeps it open until, the lever connected to the ballcock is sort of sufficiently returned to its initial position.

So the system is designed so that it sort of opens and shuts off at different orientations, and that's modulated by the water pressure. Also, just a small note here, so one disadvantage of the flapper valve system is that the valve tends to wear out, and over time it starts to leak, and this causes water wasted. You may not even notice the leakage, but it adds up over time. So in the UK, this led to an alternate valveless system called a ciphering, flush mechanism to be mandated until about 20 years ago. Many toilets in the UK still use the

siphon flush system, which works a little bit differently, but I won't describe it here, just mentioning that for our UK listeners. We now know how the cistern actually performs the flush mechanism itself and how it refills, but how does the water in the bowl escape out of it? And we also know that even after flushing is completed, there's a certain amount of water that sits at the bottom of the bowl. And so how does that stay there? Why doesn't the water just escape? So there's obviously a bit more to the plumbing going on than simply water going down the drain. So let me explain how that works. Here there's a further complication because there's at least two main different types of bowls that are used. There are probably others in other parts of the world,

but the main distinction is between syphonic bowls, which are common in America, and wash-down bowls, which are common outside of America. Now, it's very difficult to explain what the difference is between a cyphonic and a washdown bowl without showing a diagram, because conceptually they're very similar. It's just, it's really the precise design of the bowl and the shape, as well as exactly how the water is let into and how it escapes from the bowl. The easiest way to distinguish between them visually is that a syphonic bowl is, in a sense, shallower. So the water of the toilet sits higher in the bowl, and it's sort of broader. And that's because the bottom of the ball is not as sort of peaked.

It doesn't go as far down. Whereas a watchdown toilet is as a more sort of conic shape, the water sits lower and doesn't occupy as much space sort of laterally. This can have the disadvantage that waste is sort of concentrated in a narrower spot further down in the bottom of the bowl, which can lead to clogging sometimes. Of course, siphonic balls can clog as well. But that's the easiest way to distinguish between them. It's sort of how high the water sits and how broad it sits

at the bottom of the ball based on the sort of shape. The easiest way is just to look this up on Google Images if you're curious about the difference. But I'm not going to focus too much on that. Here, I just want to describe the basic mechanism of the S-bend or the trap. And I mentioned earlier that Alexander Cumming invented the S-Bend in 1775. Thomas Krap invented the U-Bend in 1880. These days, neither of those is widely used, at least in newer designs. Newer designs use a P-trap, a P-Bend trap, although I'm.

I think they're typically called p traps. So this is all a bit confusing, right? What's with all these letters and why is it called a trap? First of all, some people still use the term S-bend as a general term to refer to a trap, which is a bit confusing because the S-bend isn't really used much anymore, but sometimes it's used as a generic term. So henceforth, I'm going to specify what type of design I'm talking about via the letter. And basically, the letter refers to the shape of the piping that allows the water

to escape from the toilet bowl. And by the way, the exact same design is used for sinks as well. So this applies to toilets and to sinks. The purpose of the S-band, the U-Band, and the P-Trap design, or any of these traps, is to trap water, to retain water at the bottom of the bowl after flushing and between flushes, essentially. And this happens for sinks as well.

So there's a certain amount of water that's retained out of sight in the trap. So you can't see it in a sink, but in a toilet you can see it. Now, this was a very, very important design. You might wonder, why does there need to be water there? Why does there need to always be water at the bottom of the toilet? Why do we need to trap some of the water in the piping? The reason for this is because it creates a barrier between the sewer, which obviously your toilet is connected to, and your house.

What you don't want is a direct air passage from your house to the sewer. This is very dangerous. This prevents sewer gases from exiting up through the toilet bowl and not only spreading noxious odors, but potentially disease as well. So that's a health hazard. And so the invention of the trap creates a direct barrier of water. So essentially there's air and then there's the water that's stuck in the trap and then there's more air which sort of directly connects to the sewer. So the water provides a gap that prevents that air, prevents the sewer gas from travelling. back up into your house. So the S-trap design, it's really very simple. So imagine an S kind of on its side, right? So at the bottom of the toilet, you go down and then around up again and then down again. So it's down, around up, around down. That's the S shape. The idea is that in the down part,

the, so just at the bottom of the piping that comes out from the base of the toilet, before it goes up again, that is the trap. That's where the water will be trapped. There'll be a lower point there, which is where some water sits. And water will be retained there even after the flush. So that was the original S-trap design, because the piping has an S-shape. The U-trap, or the U-Bend, was an improvement of that that just has a U-shape. But that's not used so much anymore, and that's been replaced by an improvement, which is the P-trape. So for simplicity, I'm just going to compare an old S trap with a P trap design. And a P trap is a P shape, right? So again, think of it just as the S is on its side, the P is also on its side.

So instead of in the S trap where the piping goes down, around, up, around and down again, in the P trap, the first part's the same, so it goes down, around up, but instead of going around down again, it just goes sideways, right? So instead of an S, you have a P shape. It's down, around up, so that's the curve of the P, and then the first part is the curve of the P, and then the the straight part of the P is just sideways, and eventually it then connects to a vertical pipe that is connected to the rest of the sewer. So the core difference really is just that instead of going down, around, up, around, and down again, in an S shape, there's an extended horizontal piping

that connects between the trap and the rest of the sewer. That horizontal piping is very important, and that's the main difference between the S and the P trap. and the reason for that horizontal piping that makes p traps superior to s traps is because it prevents siphoning of the water that's in the trap out into the the sewer system which basically renders the trap ineffective the trap only works if there's some water that's retained in that lower part of it but in an s bend design that water that's held in the trap can actually be sucked out it can be siphoned out through a siphon mechanism So the siphon mechanism is very interesting. This actually, if you're not familiar with how this works, and I don't think I have actually explained it before, a siphon is an inverted U-shaped tube, which you then connect to two reservoirs,

so like just two buckets of water, for example. And what can happen is that the liquid can actually flow uphill. It can flow up to the top of the U-shaped pipe and then down again, so that the water moves from one container to the other, as long as it's one of the buckets is held at a higher. higher up. So imagine putting one bucket on a shelf and the other on the floor, filling them both with water, and then you connect them with an inverted U-shaped pipe. So initially, if there's just air in the pipe, nothing will happen. But if you can suck the air, for example, you can use your mouth to do this. People have been known to do this to siphon petrol out of cars. If you suck the air out of the

U-shaped pipe, then what will happen actually, I think it does depend on the diameter of their pipe, but with the right diameter pipe, the water will actually flow up into the pipe and down from the bucket that's on the shelf to the bucket that's on the floor. Effectively what's happening here is that gravity is pushing the water up the, up the pipe and down again and thereby allowing the water to move to the lower position. This siphon mechanism can actually cause the water in the lower position. lower part of the S-trap to be sucked out and to no longer serve the function of providing a barrier between your toilet or sink and the rest of the series system. The solution to this is a P-trap

which provides a very or a relatively long horizontal passage which makes siphoning, if not impossible, at least extremely difficult because now it's not just going kind of up and down, but you have to pass this very long horizontal passage which is much more difficult. So P-traps are better because there's much less, much, reduced chance that the water can be sucked out or siphoned away. And so what actually happens then when your toilet flushes is that obviously all of the water in the bowl that's collected from the cistern is now released. It starts to fill up the piping. It fills it up to a level where the water is now kind of overflows into the horizontal portion of the pipe. So normally the water just sits

below the horizontal portion so that it's stuck there, it's trapped there. It's just the curved part of the pea that's filled with water. But if there's now an inflow of water from the from the toilet bowl, Now water on both sides will rise up, and the water level then reaches a point where it's high enough that it can now escape by the horizontal portion of the P-trap, and now the water flows out into the service system and escapes. That process continues until there's no more water left in the toilet bowl, at which point the water level in the pipe drops, and it continues to drop until now there's no water in the horizontal portion of the P-trap, and it's thereby stops flowing. What you have left is just the little bit of water that's in the curved part of the P, which is the trap part, the trap seal, which prevents the sewer gas from escaping and getting into your, coming up through your toilet bolt. So that's how the P-trap mechanism works. Again, S-trap is essentially the same. It's just that it does have this risk of siphoning off of the water

due to this ability of atmospheric pressure to basically push water uphill a short distance to move to a lower height. and this siphoning can be avoided by just having a very long horizontal portion, which is what a pea trap uses, to prevent the water that's held in the trap from escaping. So varying ingenious mechanisms which allow our wastes to be readily removed using water, and basically just water and gravity and some levers and seals, which is what makes it all work. And that brings us to a conclusion of this 150th episode. So I hope you found this interesting and enjoyable.

If so, let me know. My email address is Fods12 at gmail.com. That's FODS12 at gmail.com. Let me know in particular if you'd be interested in hearing more of these kind of how stuff works slash engineering type episodes because there's plenty more of things that I can cover, especially now that we've got a decent background with much of the basic sort of physics and chemistry, which will be relevant for discussing some of these things.

And we already saw in today's episode how I had to appeal to quite a few different concepts that we've discussed in in the past. If you would like to support the show, you can do so by becoming a supporter on Patreon. So just Google Science of Everything podcast Patreon and you can sign up to be a monthly supporter there. You can also make a one-off donation via PayPal if you would like to support the show that way. Another way to support that doesn't require any money is to give the podcast a favorable review

on the aggregate of your choice. Most people these days listen on Spotify, but wherever you listen, you can give a review there. So just before concluding, let me talk a little bit about the history and future of the show. So I've started the show about 14 years ago now, and there have been a few interregnums in that time, but the show's been going more or less consistently for that duration. And I intend to keep the show going into the indefinite future. At the moment, I'm just finishing my PhD, so I should be submitting within a month or two, and thereafter I'll be hopefully finding a postdoc and continuing to work in academia.

So throughout the 14 years that I've been making this show, basically been studying first undergrad and then postgrad for a number of years. And so now hoping to fully transition into researcher phase. So I still intend to keep the show going, as I've said, and I don't see any reason why that should change. One of the things that I am thinking about is topics to cover, because we're now reaching the point where I have actually covered a good portion of the topics in certainly the basic natural sciences that I wanted to cover. Physics and chemistry and earth sciences are looking quite good in terms of the range of coverage. There are still a number of topics that I do want to include. So one of the things that I am intending to do going forward is to

spend a bit more time covering topics in social sciences. And I think this is increasingly important in today's world where a lot of people actually make important decisions about voting and about where they live and about career choice and other things based on opinions they have about how society works, how the economy works, how government works, which are not necessarily based on evidence or inaccurate understanding of things. So I have done a number of episodes covering politics, like political science and economics in the past. I would like to cover that, I would like to do some more coverage of that and expand coverage of social psychology and sociology as well. So that's something that I'm looking to do in the future. Those episodes can potentially

take more time because there's more empirical research that I need to look at. but it's something that I'm hoping to do. So one thing that I do know is that these episodes don't tend to get as many downloads. So let me know if you're a listener who maybe prefers the physical science episodes or if you're interested in the social science aspects or if you have some sort of thoughts or suggestions there. I'm just kind of generally interested in your feedback there. I would like to cover that and think it's important,

but I am aware of the fact that there tends to be less interest from my listeners there. So if there's any aspect that you would like to comment on or suggestions about what would make it more interesting, please do let me know. Another thing that I sort of mentioned is that I'm interested in doing more of these how stuff works slash sort of engineering style episodes. And if that's something you'd be interested in, let me know also if there's any particular topics that would be of interest. Another thing that I wanted to mention is that for about two years now I've been working with a number of editors on bringing the podcast to YouTube. So if you're a longer time listening, you may be aware that I've been talking about this for some years. Starting with this year, I've been progressively releasing edited episodes onto YouTube. So the audio is essentially unchanged, but the episodes now include visual aids, so diagrams and images to augment the experience.

and bring that to YouTube. That takes a fair bit of effort, so I've been paying a number of editors to help me with the process. It's coming along quite well, so we have a few dozen episodes now on the YouTube channel, just type Science of Everything podcast on YouTube to find that. I think about 60% of the archive of episodes

have now been edited and more being done as we speak. If you're interested in participating in this project, send me an email and let me know. Again, that's Fods12.g.g.com. F-O-D-S-1-2 at g-mall.com. I'm hoping to to complete that process, at least, of editing the episodes and getting them ready for a release

next year. I've been thinking about what I would like to do, where I would like to go next in terms of further developing the material and the podcast, because the podcast is really a means to an end, and the end is basically science communication, and also, to an extent, promoting critical thinking

and a broader understanding of the world. So, I have some ideas about this, and one is, basically bringing the show notes. So I have notes that I produce for myself while researching and they help me to, as I record the episode. I do plan on putting those up on my website. I've been working on that periodically, and that is something that I want to do next year. A number of people ask about this, and it's something I mentioned in the past as well that I had show notes, and I've sort of changed up the way that I make those available. And currently, I don't have a mechanism for that.

But basically, I'm hoping to put them all up at some point next year. I just want to to make sure that, you know, the quality and consistency is there. But also, I would like to extend beyond just having a bunch of PDFs to actually create basically a hyperlinked, you know, website design with information about all of the different episodes that I've talked about and that's added to as I produce new episodes. And ideally, this could link to sources and images and other things like that. This would take quite a bit of work. So if anyone is interested in that project, please do reach out.

So that is unlike the video editing, side of things. I haven't thought out exactly how that's going to work or what that would look like. So it's very much sort of early days and probably wouldn't start on it for a few months anyway because I want to get the video editing finished first. But it's something I've been thinking about and I thought it would be something to mention at this sort of juncture of the 150th episode because I would ultimately like to have sort of audiovisual and written forms of all of the episodes it's available for people to access depending on what your preferred method of consuming information is.

And I don't know if I've explicitly stated this before, although I've said things, I've seen things along similar lines, but the ultimate goal is for the podcast and associated materials to provide the sort of core content that you would learn in an undergraduate degree majoring in any of the social sciences or the natural sciences. So not the content in terms of things like how to solve equations or, you know, doing field work or designing experiments, procedural sort of things or how to write an essay or research, but really just the conceptual and empirical side of things, like the learning of the results and the theories and the findings, that sort of side of things. Because the game here is not to teach people how to be researchers or practitioners, but it's to teach people to help people to learn about how things work based on what we've learned. So the ultimate goal is to have all of the content and materials there of basically an undergraduate level major, maybe for certain things, a little bit of graduate level stuff.

So we've definitely done some graduate level physics content in some of our episodes, for example. So like an advanced undergraduate level, and to have that all sort of well-organized, systematically set out and freely available. We're already a good way along towards that goal, but there's still quite a ways to go yet. I estimate that at the rate that I'm producing episodes, it might take about another 10 years to get there, but I've already been going for 14 years so far, so what's another 10 years, hey? Anyway, so I hope that you stick around for that. I know that people often listen to my episodes faster than I release them, so people will binge for a while and then maybe take a break for a year or two and then come back, and that's fine,

but I hope to see you around for the duration until I get to the ultimate goal of kind of finishing all the topics that I want to, which, as I said, will take probably at least another 10 years. But until then, I'll talk to you next time.