Grandma Moon Speaks: What is Sound?

Topics Covered:

  • What is Sound?
  • Speed of Sound

The eyes see everything but themselves – Yugoslavian Proverb

Sound is a sensation perceived by ears due to vibrations or oscillations. One big difference between sound and light is that sound needs a medium for propagation. You can’t hear anything in a vacuum, which is why you can’t talk to one another in outer space.

Listening to a stampeding herd of buffaloes standing up isn’t the same as listening to them with ears on the ground. Talking to your friend underwater isn’t the same as voice chat.


The most important thing to understand about sound is that it is not absolute, and its affect changes according to the medium it propagates in. Moving a wall five feet in a studio can drastically alter the effect produced. Tilting your head sideways just a fraction will change the way you hear your favorite song.

A small change in your tone can produce an unintended perception of yourself to a listener. It doesn’t take much to start a war.

Like light, sound, too, is waves:

Things move, and they produce sounds. It could be atoms, air (wind), water or a dinosaur. Any physical object can create the perception of sound.

You’ll find that it shares many similarities to how light is perceived because of its wave nature.

One of these properties is its speed. The speed of sound in air is approximately 340.29 m/s. In steel, it is about 5,960 m/s, which is why you see your favorite movie star putting his ears on railway tracks.

An approaching train will produce vibrations that are capable of producing a perception of sound. These vibrations will travel via air and the tracks, but because it is faster through steel, it will reach our hero first, and he’ll save the day – or die trying.

Takeaways:

  • Sound is a sensation perceived by ears due to vibrations or oscillations.
  • The speed of sound in air is approximately 340.29 m/s.
  • Sound needs a physical medium for propagation.

Links for further study:

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