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What is the sound made by a falling bomb ?


It may appear to be an obvious idea, as it's become part of the language of cinematography in cartoons. The sound of a falling bomb is supposed to be a whistling sound which descends in tone, ending in an explosion. But let's look at it a bit closer and it seems less obvious.

The immediate idea is that as the bomb descends in altitude, the sound descends in pitch. It makes poetic sense, but this isn't matched by the physics, as tone rising or falling doesn't correspond with height above the ground.

The change in sound might be more to do with the Doppler effect than with height. You know how a passing ambulance has the siren pitch higher as it approached than after it's passed, well it could be that if you're in a plane that's just dropped a bomb, the bomb makes a sound which is receding ever faster, so the pitch appears to descend.

From the point of view of an observer on the ground, the sound would be different, and might conceivably be a RISING tone! There are two problems with this: Firstly, the observer would have to survive to tell the tale for this phenomenon to be reported, and secondly, if the bomb arrived at a final velocity which was supersonic, the sound would arrive after the bomb. So in theory, the sound would be a loud bang followed by a silence and then a rising tone.

From inside the plane, the sound of a falling bomb would indeed be a descending whistling sound, as the bomb accelerated away under gravity. Surviving stories would thus show that version of the sound, not the one from the ground!

Movie footage taken from bombers seems to show a sound made by each bomb, a descending tone which fades away as the bomb goes off into the distance. The explosions of impacts occur much later.

The question of bombs sounding different from the ground is interesting. It's a bit like relativity, where things are different from different perspectives. (The sound of an ambulance siren from the driver's perspective doesn't change just because it passes someone).

Surely someone must have first-hand knowledge of the awful truth behind the question: If you are on the ground, what does a falling bomb sound like? If you were in an air raid shelter and a bomb fell out of the sky and landed a distance away, what did it sound like? I expect someone will know. Over the years a great many people have been bombed from the air, by various militaristic powers, and some of the people will have survived.

Most WW2 bombs fell at subsonic speeds, according to various online information sources. Therefore, there would have been audible noise before the impact.


Also see other odd things in movies