Hi and welcome back to freesicelessons.co.uk. By the end of this video you should be able to describe the differences between transverse and longitudinal waves. You should then be able to state examples of these types of waves and finally you should be able to describe evidence that when waves are moving it's the wave that moves and not the medium.
I'm showing you here two examples of waves. We've got ripples on the surface of water and we've got sound waves traveling in air. All types of waves fall into one of two categories and these are transverse waves and longitudinal waves. Ripples on the surface of water are an example of transverse waves, whereas sound waves traveling in air are an example of longitudinal waves.
I should point out that there are many different examples of waves and we're going to be looking at several in this topic. However, remember that all waves are either transverse or longitudinal. Now one key fact about waves is that all waves transfer energy from one place to another.
Ripples transfer kinetic energy and sound waves transfer sound energy. So let's start by looking at transverse waves, for example ripples on the surface of water. I'm showing you a transverse wave here.
As you can see the wave is moving up and down. Scientists call these movements oscillations. This arrow shows the direction of energy transfer. Now the key fact is that in transverse waves the oscillations are perpendicular to the direction of energy transfer.
And the word perpendicular means at right angles. So as you can see in a transverse wave the oscillations are up and down, but the direction of energy transfer is sideways. Okay, we're going to look now at the second category of waves. These are longitudinal waves and I'm showing you a longitudinal wave here.
Now a good example of a longitudinal wave are sound waves traveling through air. Sound waves travel as particles in the air move from side to side. So here I'm showing you the air particles.
You can see that we've got regions where the air particles are very close together. Scientists call these regions compressions. In between the compressions we've got regions where the air particles are spaced out. and scientists call these regions rarefactions. Here I've paused the wave so you can see the compressions and rarefactions more clearly.
Now unlike with transverse waves, the key feature of a longitudinal wave is that the oscillations are parallel to the direction of energy transfer, and we can see that here. Now there is one other key difference between transverse and longitudinal waves. All longitudinal waves require a medium to travel in.
For example air, a liquid or a solid. In contrast not all transverse waves require a medium and we're going to look at some of those in later videos. Now there's one really important fact that you need to learn about waves. For both ripples on a water surface and sound waves in air, it's the wave that travels and not the water or the air.
We can see that using a slinky. This shows transverse waves and this represents ripples on the surface of water. The red dot shows a single point and this could represent a water molecule. As you can see when the wave travels through the dot oscillates up and down but it does not travel along the medium.
Now I'm sending longitudinal waves along the slinky. This represents sound waves traveling through air and the red dot represents an air particle. As you can see the red dot oscillates from side to side but again it does not travel through the medium.
Remember you'll find plenty of questions on transverse and longitudinal waves in my revision workbook and you can get that by clicking on the link above.