Everything Everywhere Daily: History, Science, Geography & More - The Speed of Sound

Starting point is 00:00:00 Sound travels fast. Very fast. However, it's not so fast that we can't recognize the fact that it has a finite speed. The speed of sound was estimated and later measured centuries ago, but it was only recently that it's been possible to actually travel faster than the speed of sound. It turns out that while it's possible to travel faster than the speed of sound, there's a whole host of problems that go along with it. Learn more about the speed of sound on this episode of Everything Everywhere Daily. What if your perceptions about the past were wrong? ThruLine is a podcast that takes you back in time to uncover the parts of the story that may have gone unnoticed. It effectively turned day into night. And how it shaped the world now.

Starting point is 00:00:58 Time travel with us every week on the ThruLine podcast from NPR. Before I get too far into the speed of sound, I should at least briefly explain what sound is and how it works. Sound is nothing more than a wave that travels through a material medium. We mostly encounter sound waves as it travels through air, but it can also travel through solids and liquids as well. A sound wave is not so much the movement of atoms and molecules as it is energy going through those particles. One particle is pushed slightly, which pushes the particle next to it, which pushes the particle next to it, and so on. What is moving through the medium is kinetic energy. The maximum speed that these waves can go through something,

Starting point is 00:01:44 is called the speed of sound. Unlike light, there is no one speed of sound. The speed of sound will differ depending on the substance that the sound wave is moving through. Generally speaking, sound moves faster through solids than liquids and faster through liquids than gases. The two major factors that determine how fast sound moves through a substance are density and temperature. For the rest of this episode, however, I'm going to be dealing with the speed of sound in the atmosphere at somewhat normal pressures and temperatures, because that is how we normally experience sound. The speed of light and the speed of sound are both very fast with respect to speeds humans can comprehend. However, there is an enormous difference between the two. If you've ever heard thunder

Starting point is 00:02:29 seconds after you saw lightning bolt, then you've experienced firsthand the difference in speed between the two. If you've ever been somewhere where you could hear an echo of your voice, then you've also experienced the speed of sound. One of the first attempts to measure the speed of sound was made in 1635 by the French philosopher Pierre Gascendi. He assumed that the speed of light was instantaneous, so he measured the time between seeing the flash of light from a gun and hearing the sound. He did this over various distances on days with no wind. The value he obtained was 478.4 meters per second, or 1,5169.4.2.6.9. feet per second, which was actually too high, but he did figure out that the speed of sound

Starting point is 00:03:14 was independent of the frequency of the sound. Isaac Newton took a stab at trying to estimate the speed of sound just based on calculations. His first estimate was off by about 15% because he didn't know precisely how heat affected sound. However, by the mid-18th century, the measurement of the speed of sound was shockingly accurate given the instruments at the time. They had measured it at 332 meters. meters per second. Over time, this measurement was refined. By 1942, it had been measured at 331.45 meters per second. The currently accepted measurement of the speed of sound at 0 degree centigrade or 32 degrees Fahrenheit is 331 meters per second, or 186 feet per second. Or, to put it yet another way, sound travels at

Starting point is 00:04:03 1,192 kilometers per hour, or 740 miles per hour. Once the speed of sound was established, it raised the question of what happens if you go faster than the speed of sound? This was mostly a theoretical question up until the 20th century. Airplanes kept flying faster and faster, but they were never able to go faster than the speed of sound. Some engineers actually thought that there was a sound barrier and that it was impossible to fly faster than the speed of sound. Some pilots of propeller-driven aircraft believe that they had broken the sound barrier in power dives, but it turns out that there were just problems with their instrumentation. An entire system of measurement for supersonic speeds was developed by the

Starting point is 00:04:46 Austrian physicist Ernst Mach. He developed the system that bears his name, which measure speeds relative to the speed of sound. Under the system, the speed of sound is Mach 1. Twice the speed of sound is mock two, etc. The first person to actually break the sound barrier was Colonel Chuck Yeager, who flew faster than the speed of sound on October 14, 1947. He did it in the specially designed Bell X-1 rocket aircraft. The quest to break the speed of sound, I will leave for another episode, but suffice it to say it was a huge achievement, even if it wasn't made public until nine months after it happened. One of the things that ground observers noticed when Yeager broke the sound barrier was a very loud noise. It was the world's first sonic boom. Well, technically it wasn't

Starting point is 00:05:35 the world's first sonic boom. There have been lots of them, but it was the first that could be identified as a sonic boom. And here I should explain exactly what a sonic boom is, because there's a great deal of confusion about the matter. A sonic boom is a shockwave created when an object, such as an aircraft or a bullet, travels through the air at a speed faster than the speed of sound. It occurs because the object displaces air faster than the molecules can move out of the way, causing a buildup of pressure that is released as a sonic boom. When I say that Chuck Yeager didn't really create the first sonic boom, it's because small sonic booms occur whenever high-calibur bullets are fired or artillery shells are launched.

Starting point is 00:06:17 Most people have no clue that these are sonic booms, because they occur almost simultaneously with the explosion of gunpowder, which also causes a loud noise. Perhaps the simplest sonic boom you might be familiar with is the cracking of a whip. A whip makes a distinctive cracking sound because the tip of the whip very briefly goes faster than the speed of sound, resulting in a very small sonic boom. In the case of an aircraft creating a sonic boom, the aircraft is much larger, which results in a much larger shockwave, aka sonic boom,

Starting point is 00:06:48 and because of its altitude, it can be heard over a much greater distance. There's one big misconception people have about sonic booms. They assume that it's something that only occurs a single time when a plane passes Mach 1. And this is incorrect. A plane is continually making a sonic boom so long as it's flying above the speed of sound. A sonic boom is actually analogous to a wake created by a fast-moving boat. A boat will create a two-dimensional wake behind it, but a plane will create a three-dimensional wake behind it in the series.

Starting point is 00:07:22 shape of a cone. When the cone reaches the ground, it will do so in the shape of an arc. That arc will follow the plane as it flies. And this is known as the sonic boom carpet. Another thing that most people don't realize is that all sonic booms are actually double sonic booms. There is a boom when you hear the shock wave and another when the pressure returns to normal. However, most airplanes will produce sonic booms that are so close together that they sound like one boom. When the space shuttle re-entered the atmosphere, it produced a very noticeable double sonic boom, and this was due to the larger size of the orbiter and the shockwave that it created. Sonic booms cannot be heard by people inside the aircraft that creates them. That's because they're literally traveling faster than sound, and the

Starting point is 00:08:09 pressure wave can't catch up to them. The issue of sonic booms has actually been a sticking point for supersonic travel. Most people have wondered why commercial air travel hasn't gotten any faster over the years. And the truth is, we have the technology to fly passengers faster than the speed of sound. We've had it for decades. The Concord was an aircraft that flew at supersonic speeds across the Atlantic for years. From 1976 until 2003, the Concord flew passengers on a regular schedule. It actually set the record for transcontinental commercial travel on February 7, 1996, when it went from New York JFK to Heathrow in just two hours, 52 minutes, and 59 seconds.

Starting point is 00:08:50 It was aided on that flight by a 175 mile an hour or 282 kilometer per hour tailwind. However, the Concord was limited to flying over the ocean because of the problem with sonic booms. If a plane the size of a Concord flew from New York to Los Angeles entirely overland, it would lay down a sonic boom carpet across the entire country. The higher the altitude of plane flies, the wider the sonic boom carpet will be. A plane fly in an altitude of 50,000 feet or 15.1.5.5.5.5. kilometers will create a sonic boom carpet 50 miles or 80.4 kilometers wide. Sonic booms are extremely annoying and can cause damage. NASA and the Federal Aviation

Starting point is 00:09:32 Administration ran tests in 1964 over Oklahoma City. For six months, they created eight sonic booms a day over Oklahoma City, and the end result was 15,000 registered complaints and a class action lawsuit. Many countries have banned or put restrictions on sonic booms for this reason. It's also resulted in one of the most active areas of aeronautical research. The intensity of a sonic boom can be mitigated by the shape of an aircraft and how it creates the shockwave cone that follows it. One method was to try to shape the cone so it would expend most of its energy horizontally instead of vertically. In 2018, NASA commissioned Lockheed Martin to build the X-59 quest, which hopefully will demonstrate that a sonic boom can be kept as quiet

Starting point is 00:10:16 as closing a car door. I should also note the theoretical design called a Buseman biplane. The Buseman biplane has two wings that would, in theory, create no sonic boom at all. However, the design would also not provide any lift, which is important for an airplane wing. Another design that's being considered

Starting point is 00:10:36 is just making planes smaller. There are current proposals on the board for supersonic private jets, which would make less noise simply due to their size. The current record for supersonic airtrients, was sent back in 1976 by the SR-71 Blackbird, on which I've done a previous episode. But the pursuit of breaking the sound barrier wasn't just something that occurred in the air. There were also attempts for decades to break the sound barrier on land.

Starting point is 00:11:00 The land sound barrier was broken on October 15, 1997, by British RAF pilot Andy Green, who drove the jet-powered thrust SSC past Mach 1 in the Black Rock Desert of Nevada. To date, it is the only time any land vehicle has ever broken the. the sound barrier. The speed of sound is no longer a seemingly impossible barrier to overcome. It's broken on a daily basis by military aircraft, and it was broken on a regular basis for years by the Concord. Today, the sound barrier is something to be tamed and controlled.

Starting point is 00:11:33 Perhaps a future generation of aircraft that can dampen sonic booms will allow everyone the ability to finally travel faster than the speed of sound. The executive producer of Everything Everywhere Daily is Charles Daniel. The associate producers are Peter Bennett and Cameron Kiefer. Today's review comes from listener Brenda over on CastBox. They write? I'm not sure if Gary C's comments here or not, but five stars. After changing jobs a year ago, I went from doing my bookkeeping and answering a phone

Starting point is 00:12:03 to just entering bookkeeping data. I started out listening to just music, then tried out audiobooks and podcasts. Several sounded interesting, but the narrator-slash-podcaster's voice was not pleasant to my ears. Gary is a smooth voice that is easy to listen to. in less than three months I have listened to every one of the podcasts. Great job, Gary. Well, thanks, Brenda. As you can see, I do notice the comments that are left over on CastBox. I'm glad to keep you company during your workday. You can be both productive as well as learn something in the process.

Starting point is 00:12:32 And of course, welcome to the Completionist Club. Remember, if you leave a review or send me a boostagram, you two can have it read on the show.

Everything Everywhere Daily: History, Science, Geography & More - The Speed of Sound

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