a students' magazine / Physics

Two wings “is megl’ che one!” (1) Some notes about sound.

Hi guys!

I apologize if the title makes your mouth water but I won’t talk about ice creams! 🙂

I’d like to share with you something I read a few days ago on a magazine about a new prototype of a supersonic airplane.

But I need to explain something about sound first.

We define “sound” the sensation that we perceive as the consequence of a vibrating body. The body transmits its movement to the particles close to it, which start to vibrate causing a variation in pressure, that our hear perceives.

Sound is a wave, so it has a particular speed of propagation, equal to 1193,4 km/h at 0 °C.  As far as  propagation of sound in fluids is concerned, if a body is faster than sound we say it has a supersonic speed;  if it is slower, it has a subsonic speed.

Supersonic speed produces a shockwave, a wave of propagation faster than the transonic wave; crashing together they produce a very fast and large variation in pressure and temperature, that we perceive as a sound (bOOm): the sonic boom.

Did you know that you can simply buy an object that overtakes the speed of sound without buying an airplane and a hangar to park it?

The whip is in fact the first object created by man that breaks the sound barrier. In particular, when you crack a whip, its end is faster than sound, and causes the sonic boom.

The sonic boom created some problems to airplanes during WWII when fighter bombers trying dive-bombing showed difficulties to keep the flight path because of vibrations on aerodynamic areas and the inversion of the controls (roll reversal) .

Moreover, many airplanes exploded while flying because of the shockwave, as if they had crashed into a wall. For this reason people started talking about a “sound barrier“.

After many studies, attempts, failures and deaths (among which we remember Geoffrey de Havilland Jr.,  or the Mitsubishi Zero), in 1948 the British Air Force together with the “Miles Aircraft” gave birth to the BELL X-1 piloted by  Charles “Chuck” Yeager, the first man who overtook the speed of sound while flying horizontally reaching the speed of  Mach 1,5.

This is an exiting exctract from the French film “L’étoffe des héros” that reproduces those glorious moments!

While this is a historical documentary of the event:

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