The sonic boom problem - Katerina Kaouri - video Dailymotion

TED-Ed

Objects that fly faster than the speed of sound (like really fast planes) create a shock wave accompanied by a thunder-like noise: the sonic boom. These epic sounds can cause distress to people and animals and even damage nearby buildings. Katerina Kaouri details how scientists use math to predict sonic booms' paths in the atmosphere, where they will land, and how loud they will be.  Lesson by Katerina Kaouri, animation by Anton Bogaty.

Transcript

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...

The sonic boom problem - Katerina Kaouri

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