Doppler Effect and Shock Waves HD

Ordinary sound waves propagate forward in the direction of source motion, overtaking it, and back. Due to Doppler effect the still receiver located ahead a source detects a sound with the greater frequency, than emitted. If detector is behind of source, then the received frequency will be lower then emitted. In the first part of animation the rings show the surfaces of equal phase in the sound wave generated by a source. We see, that ahead of a source the density of such lines is more than behind of it. Because the speed of sound relatively the media is equal in all directions, the frequency of sound ahead a source and behind of it will be different.

Let's consider an object which moves with speed of sound (the plane, for example). At each moment of time it will radiate a circular sound wave. Because the speed of source coincides with speed of sound, emitted waves superpose each other and there is a jump of pressure (front of a shock wave) ahead of source as shown in second part of animation.

Next let's consider a case when the source of a sound moves with supersonic speed (in animation the source moves with double speed of sound). In this case sound waves can not overtake a source and for this reason there are no sound waves before a source, they appear only behind of it. Sound waves arising behind a source superpose with each other and form in space a conic surface of high pressure. This surface is a shock wave. It is easy to show, that a sine of the angle formed by front of a shock wave with a direction of movement of a source is equal to the ratio of speed of sound to speed of source (i.e. it is the reciprocal of Mach number).

http://physics-animations.com/

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Science & Technology

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• swdzu

[ladiestreat27]

what if you cruising behind the plane while the jet is going supersonic speeds, would you hear high and low frequency at the same time? if so, what does that sound like?

[physicsanimations]

@ladiestreat27

If source is moving away from the stationary observer, then f_d=f / (1+v/u), where u is the velocity of the waves, v is the velocity of jet, f is initial frequency.

[biscottie83]

this is the animation that helps u see how a fast moving object and the sound interacts ..(the circles are sound waves)

first plane, slower than the sound..

second plane, braking the sound barrier

third plane, faster than the sound

[ladiestreat27]

@ELOA23 i finally got it. there is no sonic boom that can hit the plane since it moves in all directions AWAY from the plane. so no matter what the plane does, it cannot be hit by the sonic boom. (unless it  over shot the sonic boom to the left or right and waited for it to reach it again but that is not realistic.)

[MILOPKM]

A little annotation would have done any harm. Such as denoting

- Subsonic for the 1st flight.

- Transonic flow for 2nd

- Sonic for 3rd

[ponderainnovation]

Hi, its really cool what we contribute. I'm doing the same thing

[ultrasonictechnology]

thanks for explaining

[StandingRedPanda]

Whoa! I finally found a science video without someone arguing about religion :D

But anyway, I have never seen how shockwaves travel when the jet goes faster than the sound. This is fun! So if you would be in front of the jet, you wouldn't hear it at all.

[AnnihilatorCZ]

@zmailzzz Wzum wzum wzum!

[zmailzzz]

but I can move faster than the right.

[xCRsoccerboy]

i understand it

[ELOA23]

@ladiestreat27 yes, that's what happens when the aircraft would reach the speed of sound again, but the mach cone it produced while supersonic wouldn't hit it because the "sonic boom" doesn't move on its own and is created by the airplane.

[ladiestreat27]

@c03rcion so the pilot will hear the sound but not the boom since it is going outwards yup i get it now.