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Sound, Compression and Rarefaction

Sound, Compression and Rarefaction

Sound, Compression and Rarefaction

Sound waves are longitudinal, mechanical waves. They are created by particles undergoing high pressure then low pressure, which creates compressions and rarefactions.

Sound is made up of waves. What kind of wave?

For longitudinal waves, like sound waves, oscillations vibrate _____________ to the direction of energy transfer.

1

This shows a sound wave

The oscillations travel parallel to the direction of energy transfer, so it is a longitudinal wave.

2

Now, do sound waves require a medium to be able to travel? Answer yes or no.

3

So sound waves do require a medium to be able to travel

They require particles to vibrate in order to propagate, so if there are no particles there can be no sound waves!

4

Is there sound in outer space? Answer yes or no.

5

What do we call waves that need a medium to propagate?

A) Electromagnetic waves B) Mechanical waves

Recap

1

Sound waves are longitudinal waves

Their oscillations travel parallel to the direction of the transfer of energy.

2

Sound waves are mechanical waves

They need a medium (particles) to propagate.

1

True or false? When sound waves use air particles to propagate, those particles travel with the wave.

2

Waves, including sound waves, are the transfer of energy only!

Matter (like particles in the air) oscillates, but it returns to its original position once the wave has passed.

1

If you look closely at a booming soft speaker, you will see the surface move backwards and forwards

When it moves forwards, the speaker "pushes" at particles in the air.

2

What happens to the air particles in front of the speaker when the soft speaker pushes at them?

A) They get squished together. B) They get spread out from each other.

3

When particles get squished together, it's called compression

It's a bit like when you press the two sides of an accordion together.

4

What happens to the air particles in front of the speaker when the soft speaker retracts again?

A) They get squished together even more. B) They spread out again.

5

This non-squished state of particles is called rarefaction

It's a bit like when you pull the two sides of an accordion back out.

6

Where is particle density higher?

A) In compression B) In rarefaction

Summary

1

Sound waves are longitudinal, mechanical waves

Their oscillations travel parallel to the direction of energy transfer, and they require a medium (like air) to be able to propagate.

2

They are created by particles undergoing high pressure and then low pressure

This is called compressions and rarefactions.