What is the speed of sound

A.� The speed of sound is the speed at which a medium’s molecules pass amongst themselves, via collisions, the message that something is either approaching or retreating. An example of a medium is air.

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Q.� What causes a sonic boom

A.� When the approaching or retreating object is travelling faster than the message itself can travel, however, the molecules become more agitated and get rid of this excitement very loudly producing the sonic boom.

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Q.� Why, when the space shuttle is returning to Earth, do you hear two separate sonic booms a few seconds apart

A.� Because the front and end of the shuttle create two separate disturbances, in the same way that the front and back of a boat create two separate wakes in water. Each disturbance results in its own sonic boom.

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Even though these two booms are originally less than a second apart they’re heard as two distinct sounds. This is because by the time the booms reach the listener on the ground the original distance has been magnified because of the time it takes for the noise to travel from the point when the space shuttle re--enters the earth’s atmosphere to its surface.

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Q.� Why doesn’t Concorde produce more than one sonic boom

A.� Actually it does, but because Concorde is flying at a lower altitude than where the space shuttle re-enters the atmosphere the delay in reaching your ears on the ground is much less and so they’re heard as a single noise.

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Q.� Why don’t subsonic planes create a sonic boom

A.� Because they’re moving at less than the speed of sound the shockwave they create outstrips their own motion and so they don’t cause much of a change to the surrounding pressure and density of the air.

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by Lisa Cardy