00:00Humans have been fascinated with speed for ages.
00:10The history of human progress is one of ever-increasing velocity,
00:15and one of the most important achievements in this historical race
00:18was the breaking of the sound barrier.
00:21Not long after the first successful airplane flights,
00:24pilots were eager to push their planes to go faster and faster.
00:29But as they did so, increased turbulence and large forces on the plane
00:34prevented them from accelerating further.
00:37Some tried to circumvent the problem through risky dives,
00:41often with tragic results.
00:44Finally, in 1947, design improvements such as a movable horizontal stabilizer,
00:50the all-moving tail,
00:52allowed an American military pilot named Chuck Yeager
00:55to fly the Bell X-1 aircraft at 1,127 kilometers per hour,
01:03becoming the first person to break the sound barrier
01:06and travel faster than the speed of sound.
01:09The Bell X-1 was the first of many supersonic aircraft to follow,
01:13with later designs reaching speeds over Mach 3.
01:17Aircraft traveling at supersonic speed create a shockwave,
01:21with a thunder-like noise known as a sonic boom,
01:25which can cause distress to people and animals below,
01:29or even damage buildings.
01:31For this reason, scientists around the world have been looking at sonic booms,
01:35trying to predict their path in the atmosphere,
01:38where they will land, and how loud they will be.
01:41To better understand how scientists study sonic booms,
01:45let's start with some basics of sound.
01:48Imagine throwing a small stone in a still pond.
01:51What do you see?
01:53The stone causes waves to travel in the water at the same speed in every direction.
01:58These circles that keep growing in radius are called wave fronts.
02:03Similarly, even though we cannot see it,
02:06a stationary sound source, like a home stereo,
02:09creates sound waves traveling outward.
02:12The speed of the waves depends on factors like the altitude and temperature
02:16of the air they move through.
02:18At sea level, sound travels at about 1,225 kilometers per hour.
02:24But instead of circles on a two-dimensional surface,
02:27the wave fronts are now concentric spheres,
02:30with the sound traveling along rays perpendicular to these waves.
02:35Now imagine a moving sound source, such as a train whistle.
02:39As the source keeps moving in a certain direction,
02:42the successive waves in front of it will become bunched closer together.
02:47This greater wave frequency is the cause of the famous Doppler effect,
02:52where approaching objects sound higher pitched.
02:55But as long as the source is moving slower than the sound waves themselves,
02:59they will remain nested within each other.
03:02It's when an object goes supersonic, moving faster than the sound it makes,
03:07that the picture changes dramatically.
03:10As it overtakes sound waves it has emitted,
03:13while generating new ones from its current position,
03:15the waves are forced together, forming a mock cone.
03:19No sound is heard as it approaches an observer,
03:22because the object is traveling faster than the sound it produces.
03:27Only after the object has passed will the observer hear the sonic boom.
03:33Where the mock cone meets the ground, it forms a hyperbola,
03:37leaving a trail known as the boom carpet as it travels forward.
03:41This makes it possible to determine the area affected by a sonic boom.
03:46What about figuring out how strong a sonic boom will be?
03:49This involves solving the famous Navier-Stokes equations
03:53to find the variation of pressure in the air
03:56due to the supersonic aircraft flying through it.
03:59This results in the pressure signature known as the N-wave.
04:03What does this shape mean?
04:05Well, the sonic boom occurs when there is a sudden change in pressure,
04:09and the N-wave involves two booms,
04:12one for the initial pressure rise at the aircraft's nose
04:15and another for when the tail passes and the pressure suddenly returns to normal.
04:20This causes a double boom,
04:22but it is usually heard as a single boom by human ears.
04:26In practice, computer models using these principles
04:29can often predict the location and intensity of sonic booms
04:33for given atmospheric conditions and flight trajectories,
04:37and there is ongoing research to mitigate their effects.
04:40In the meantime, supersonic flight over land remains prohibited.
04:45So, are sonic booms a recent creation?
04:48Not exactly.
04:49While we try to find ways to silence them,
04:52a few other animals have been using sonic booms to their advantage.
04:56The gigantic Diplodocus may have been capable of cracking its tail faster than sound,
05:02at over 1,200 kilometers per hour, possibly to deter predators.
05:07Some types of shrimp can also create a similar shock wave underwater,
05:12stunning or even killing prey at a distance with just a snap of their oversized claw.
05:19So, while we humans have made great progress in our relentless pursuit of speed,
05:24it turns out that nature was there first.
05:37The ancient blooms have been built!
05:38The most important thing is to help them be able to achieve the frequency of the species.
05:41The next level of the fallen enemy is the same prophet,
05:42It might be a more physical object that doesn't matter.
05:44If you're able toly
05:45to be felt human,
05:46you might be able touate the content and in a metaphor.
05:47You might need a more physical wish.
05:48So, what do you want to do?
05:49The rest of the field can also be able to preserve the power of the sun?
05:50You might be able to preserve your physical object.
05:52To day for you for this kind of setting the world that you want to use?
05:54You might have a little bit,
05:55and you might have a little bit of taste and believe that you want to be able to derive.
05:56Maybe you might be able to do a little bit of a bit of a ten-o-o...
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