What’s that noise?


My younger daughter asks this question all the time. She only recently learnt how to ask ‘what’s that noise?’ and has become very fond of asking it! So, I thought this would be a great opportunity to talk how sounds are made and how we hear them.

What is sound?

Sound is caused by the vibration of molecules. So, something has to move for a sound to start. I find it easiest to picture this in my head, if I think about a musical instrument – like a guitar.

When you play a guitar, you pluck or strum a string on the instrument using your fingers or thumb. That plucking or strumming makes the string wobble from side to side and we call this movement a ‘vibration’.

The vibration makes molecules in the air around the string vibrate. Those air molecules bump into other air molecules around them and make them vibrate. And in this way, the vibration passes through the air and creates a ‘sound wave’.

How do you hear a sound?

Eventually, the sound waves travel all the way to your ear. Inside your ear is a flap of skin called the ‘eardrum’. When sound waves bump into your eardrum, messages are sent to your brain, which tell you that you’re hearing a sound. The messages also tell your brain information about how loud the sound is and which direction it is coming from.

If you’re interested to know more about how you hear things through your ears, this website gives a more detailed description.

Sound effects

Did you know that sound waves don’t just travel through the air? They also travel through liquids and solids. You can test this out by doing some experiments. Put your ears under the water when you’re in the bath and have a listen – what does it sound like? Or put your ear to one of the walls in your home and try to hear what’s going on in the next room! Is it easier or harder than listening to sounds through the air?

You might also like to try making your own telephone out of yogurt pots and string. When one person speaks into their yogurt pot, the sound waves from their voice will travel along the string and can be heard by the person listening to the other yogurt pot. But remember to keep the string pulled tight or it won’t work!

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