The sonic boom problem - Katerina Kaouri
-
0:07 - 0:11Humans have been fascinated
with speed for ages. -
0:11 - 0:15The history of human progress
is one of ever-increasing velocity, -
0:15 - 0:19and one of the most important achievements
in this historical race -
0:19 - 0:22was the breaking of the sound barrier.
-
0:22 - 0:25Not long after the
first successful airplane flights, -
0:25 - 0:30pilots were eager to push
their planes to go faster and faster. -
0:30 - 0:32But as they did so, increased turbulence
-
0:32 - 0:38and large forces on the plane
prevented them from accelerating further. -
0:38 - 0:42Some tried to circumvent
the problem through risky dives, -
0:42 - 0:44often with tragic results.
-
0:44 - 0:48Finally, in 1947, design improvements,
-
0:48 - 0:52such as a movable horizontal stabilizer,
the all-moving tail, -
0:52 - 0:56allowed an American military pilot
named Chuck Yeager -
0:56 - 1:04to fly the Bell X-1 aircraft
at 1127 km/hr. -
1:04 - 1:07becoming the first person
to break the sound barrier -
1:07 - 1:10and travel faster than the speed of sound.
-
1:10 - 1:14The Bell X-1 was the first of many
supersonic aircraft to follow, -
1:14 - 1:18with later designs reaching speeds
over Mach 3. -
1:18 - 1:22Aircraft traveling at supersonic speed
create a shock wave -
1:22 - 1:26with a thunder-like noise
known as a sonic boom, -
1:26 - 1:29which can cause distress to people
and animals below -
1:29 - 1:31or even damage buildings.
-
1:31 - 1:32For this reason,
-
1:32 - 1:35scientists around the world
have been looking at sonic booms, -
1:35 - 1:38trying to predict their path
in the atmosphere, -
1:38 - 1:42where they will land,
and how loud they will be. -
1:42 - 1:45To better understand
how scientists study sonic booms, -
1:45 - 1:48let's start with some basics of sound.
-
1:48 - 1:52Imagine throwing a small stone
in a still pond. -
1:52 - 1:53What do you see?
-
1:53 - 1:56The stone causes waves
to travel in the water -
1:56 - 1:59at the same speed in every direction.
-
1:59 - 2:03These circles that keep growing in radius
are called wave fronts. -
2:03 - 2:06Similarly, even though we cannot see it,
-
2:06 - 2:09a stationary sound source,
like a home stereo, -
2:09 - 2:12creates sound waves traveling outward.
-
2:12 - 2:14The speed of the waves depends on factors
-
2:14 - 2:18like the altitude and temperature
of the air they move through. -
2:18 - 2:24At sea level, sound travels
at about 1225 km/hr. -
2:24 - 2:27But instead of circles
on a two-dimensional surface, -
2:27 - 2:31the wave fronts
are now concentric spheres, -
2:31 - 2:36with the sound traveling along rays
perpendicular to these waves. -
2:36 - 2:40Now imagine a moving sound source,
such as a train whistle. -
2:40 - 2:43As the source keeps moving
in a certain direction, -
2:43 - 2:48the successive waves in front of it
will become bunched closer together. -
2:48 - 2:53This greater wave frequency is the cause
of the famous Doppler effect, -
2:53 - 2:56where approaching objects
sound higher pitched. -
2:56 - 3:00But as long as the source is moving
slower than the sound waves themselves, -
3:00 - 3:03they will remain nested within each other.
-
3:03 - 3:08It's when an object goes supersonic,
moving faster than the sound it makes, -
3:08 - 3:11that the picture changes dramatically.
-
3:11 - 3:13As it overtakes sound waves
it has emitted, -
3:13 - 3:16while generating new ones from
its current position, -
3:16 - 3:20the waves are forced together,
forming a Mach cone. -
3:20 - 3:23No sound is heard
as it approaches an observer -
3:23 - 3:28because the object is traveling faster
than the sound it produces. -
3:28 - 3:33Only after the object has passed
will the observer hear the sonic boom. -
3:33 - 3:37Where the Mach cone meets the ground,
it forms a hyperbola, -
3:37 - 3:41leaving a trail known as the boom carpet
as it travels forward. -
3:41 - 3:46This makes it possible to determine
the area affected by a sonic boom. -
3:46 - 3:49What about figuring out how strong
a sonic boom will be? -
3:49 - 3:53This involves solving the famous
Navier-Stokes equations -
3:53 - 3:56to find the variation
of pressure in the air -
3:56 - 4:00due to the supersonic aircraft
flying through it. -
4:00 - 4:04This results in the pressure signature
known as the N-wave. -
4:04 - 4:05What does this shape mean?
-
4:05 - 4:10Well, the sonic boom occurs
when there is a sudden change in pressure, -
4:10 - 4:12and the N-wave involves two booms:
-
4:12 - 4:15one for the initial pressure rise
at the aircraft's nose, -
4:15 - 4:18and another for when the tail passes,
-
4:18 - 4:21and the pressure suddenly
returns to normal. -
4:21 - 4:23This causes a double boom,
-
4:23 - 4:27but it is usually heard as a single boom
by human ears. -
4:27 - 4:30In practice, computer models
using these principles -
4:30 - 4:34can often predict the location
and intensity of sonic booms -
4:34 - 4:38for given atmospheric conditions
and flight trajectories, -
4:38 - 4:41and there is ongoing research
to mitigate their effects. -
4:41 - 4:46In the meantime, supersonic flight
over land remains prohibited. -
4:46 - 4:49So, are sonic booms a recent creation?
-
4:49 - 4:50Not exactly.
-
4:50 - 4:53While we try to find ways to silence them,
-
4:53 - 4:56a few other animals have been
using sonic booms to their advantage. -
4:56 - 5:01The gigantic Diplodocus may have been
capable of cracking its tail -
5:01 - 5:08faster than sound, at over 1200 km/hr,
possibly to deter predators. -
5:08 - 5:12Some types of shrimp can also create
a similar shock wave underwater, -
5:12 - 5:16stunning or even killing pray
at a distance -
5:16 - 5:20with just a snap of their oversized claw.
-
5:20 - 5:22So while we humans
have made great progress -
5:22 - 5:25in our relentless pursuit of speed,
-
5:25 - 5:27it turns out that nature was there first.
- Title:
- The sonic boom problem - Katerina Kaouri
- Speaker:
- Katerina Kaouri
- Description:
-
View full lesson: http://ed.ted.com/lessons/what-causes-sonic-booms-katerina-kaouri
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.
- Video Language:
- English
- Team:
- closed TED
- Project:
- TED-Ed
- Duration:
- 05:44
Krystian Aparta edited English subtitles for The sonic boom problem | ||
Krystian Aparta edited English subtitles for The sonic boom problem | ||
Jessica Ruby edited English subtitles for The sonic boom problem | ||
Jessica Ruby approved English subtitles for The sonic boom problem | ||
Jessica Ruby accepted English subtitles for The sonic boom problem | ||
Jessica Ruby edited English subtitles for The sonic boom problem | ||
Jessica Ruby edited English subtitles for The sonic boom problem | ||
Jessica Ruby edited English subtitles for The sonic boom problem |