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Why Is A Sonic Boom So Loud?

What does speed have to do with sound? And if there’s no wall in the sky, how exactly

do you break a sound barrier?

Hey guys, Amy here with you on DNews today talking speed! Fast things. Not drug things.

Most of us will probably never go supersonic. Though the idea of cutting travel times in

half is so appealing, it’s not something likely to become common place anytime soon.

But let’s start with a bit of a history lesson. In the 1880s, Austrian physicist Ernst

Mach was studying the supersonic flow of gases using a shadowgraph when he successfully photographed

a bullet traveling faster than the speed of sound. What his images showed was a bullet

with a shock wave in front of it and another one trailing behind it, clear proof of the

phenomenon of compressibility. This research eventually led to the measurements that bear

his name: a Mach number is the ratio of the speed of an object traveling through a gas

to the speed of sound in that gas.

Because while we don’t think about it, air is made up of molecules, and like any other

physical substance, those air molecules can compress, and when they compress they form

shock waves.

It’s these shock waves that make flying faster than the speed of sound such a challenge,

and in the 1940s, pilots were coming face to face with this challenge. These shock waves

vibrate the air molecules they’re made of, and when those molecules vibrate they vibrate

whatever is compressing them. In the case of a fast-flying airplane, the shock waves

can shake an airplane hard enough to rip it apart.

It was clear to engineers in the 1940s that the future of aviation lay beyond the sound

barrier, so someone would have to build an airplane solid enough and fast enough to break

through that wall.

It was the Bell Aircraft corporation working on a contract with the US Army Air Force that

devised the solution. Taking design inspiration from a bullet, Bell engineers designed the

X-1 aircraft specifically to break through that wall of compressed air in the sky.

The advent of supersonic flight opened a whole new era of aviation, and though higher Mach

numbers don't come with the same “barriers” every increase in speed is nonetheless a major

technological hurdle.

The fastest manned flight on record was set in 1967 with the NASA-Air Force X-15, a rocket-powered

dart of an aircraft that hit a top speed of Mach 6.7, which is about 4,519 mph! But the

X-15 was a hypersonics research vehicle. Most fighter jets today aren’t nearly that fast,

though there are supersonic fighters. Air Force planes like the F-15 Eagle and the F-22

Raptor are both supersonic fighter jets, and the F-22 can even hit Mach 2 using afterburners.

But there’s another challenge associated with supersonic flight and that’s the sonic

boom. The sonic boom is the sound an airplane makes when it smashes through that wall of

compressed air that builds up in front of it. But the boom doesn’t just come once

when the plane goes supersonic; it keeps going in the wake of that supersonic aircraft.

This is exactly why the Concorde, the world’s only supersonic passenger plane that flew

from 1976 to 2003, only ever flew over oceans. In fact, the Federal Aviation Administration

prohibited domestic civil supersonic flight over land in 1973. But all is not lost! NASA

and its aviation partners are looking into identifying an acceptable loudness level and

working on so-called “low boom” aircraft designs to reduce sonic boom levels and maybe

bring back supersonic passenger flights. But that’s still something to look forward to

down the line.

And the U.S. Air Force always has its eye on the future, too, and it’s a big supporter

of DNews! The United States Air Force is powered by Airmen and fueled by innovation. Every

day American Airmen go above and beyond to break barriers both professionally and personally.

Whether it’s overcoming poverty to become a nurse and officer or becoming the first

female Thunderbird pilot, these Airmen are known for doing what was once thought to be

impossible.

Have any of you flown supersonically? If so, tell us what it was link in the comments below

because I’m dying to know what it’s like! And if you haven’t, do you want to? Let

us know in the comments below and don’t forget to subscribe for more DNews every day

of the week.

Have any of you flown supersonically? If so, tell us what it was link in the comments below

because I’m dying to know what it’s like! And if you haven’t, do you want to? Let

us know in the comments below and keep coming back to Test Tube for more DNews every day

of the week.

Have any of you flown supersonically? If so, tell us what it was link in the comments below

because I’m dying to know what it’s like! And if you haven’t, do you want to? Let

us know on the Discovery News Facebook page or on Twitter @DNews. You can also find me

@astvintagespace. Thanks for watching!