What is sound and how does it travel?

Sound is also a form of energy. One way of showing that sound is a form of energy is by shouting loudly for a long time! (Don't feel that you need to do this. Let it be another 'thought experiment! Thinking takes very little energy!)

Shouting loudly for a long time makes you tired. The more loudly you shout, the more quickly you do get tired. You need to me more energy to make a louder noise.

If you are at a very noisy party, where the music is being played very loudly, through big 'speakers', you may try holding a piece of light paper, such as tissue paper near to a speaker. You will probably see some movement of the tissue.

This is because it is being 'hit' by sound waves and caused to move.

Like light, sound also moves from one place to another as 'waves', or 'ripples'. Unlike light, sound needs a 'medium' through which to move. In other words, it needs something to move through. Sound can move as waves through air,' water and even iron and steel! But sound waves cannot travel through a vacuum. Sound travels very, very much slower than light. The speed of sound through air is about

330 metres per second.