Lesson video

Hello, everyone, this is Mr. James.

And I hope that you are as happy as I am to be here today, ready to learn some more science, to learn about the world and how everything in it works.

So curiosity caps on.

Here we go.

Today's lesson is from the unit Introduction to Sound, and the title of the lesson is How Vibrations Travel.

By the end of it, it would be absolutely wonderful if you could recognise that vibrations from sounds travel through a medium to the ear, that's our learning outcome.

And to be able to explain that to somebody, you are going to need to know some special science words, some keywords, so let's have a look at those words, shall we? The first word on our list, you might recognise from the title of the lesson, How Vibrations Travel.

So the word is vibrations.

I'll say the words.

If you like, you can repeat them after me, I'll leave a little gap.

So we have vibrations, medium, diagram, and sound waves.

So just take a moment to think for yourself, "Have I ever seen those words before? And what do I think each of them means?" Sometimes in our language, one word is used to mean different things, like the word medium, for instance.

You might have been asked when you were in the lunch queue, for instance, queuing up, whether you wanted a larger medium or a small potato.

But in this case, medium means something a little different, as we'll see.

Yes, it's not talking about the size of things.

So vibrations are when an object moves very fast from side to side, but those vibrations need something to travel in, and that's what a medium is, the thing that those sound vibrations, those vibrations are travelling in.

And that could be a solid medium, like a tabletop, or it could be a liquid medium, like the water in the swimming pool, or it could be a gas medium, like the air that surrounds us, the air that we breathe.

So what about a diagram? Well, a diagram is a simplified drawing of information, a simple drawing.

So it's not the sort of drawing where you spend ages colouring in and decorating and thinking of how pretty it's all going to look.

It's more about the information that it contains, keeping it simple and clear.

Vibrations travel in sound waves, and they spread out in all directions, as we're about to see.

Our lesson is split into three parts.

So we start by thinking about what sounds actually are, and then we'll go on to think about how sounds are heard, and then we'll go back to those mediums, those different mediums, through which we can hear sound.

Let's take a moment first to have a chat with a partner, with someone next to us.

Let's tell them about our own ideas and our own experiences of sound and how we think it's made.

So pause the video now and have a talk with somebody near to you.

Fabulous.

I wonder what ideas you shared.

So a sound is made when an object vibrates, and a vibration is a repeated forwards and backwards movement.

Here's an example, if I take my ukulele, and I play one of the strings, (ukulele string resonating) the string will vibrate, it will go forwards and backwards, and then the sound will travel, the sound wave will travel through the air to the ear of, or to my ear, or to the ear of a listener.

We don't always see those vibrations, but sometimes we can feel them, or we can see their effect on something.

And here's an example, in the picture, you can see somebody's holding their hand against a speaker, a loudspeaker.

Have you ever done that? Have you ever put your face or your cheek up against a speaker, or have you held your hand there and felt the air, the air moving as the sound is made by the speaker? Which part of your body hears sounds? Can you point to it? Yes, of course, you can.

It's your ears.

And our ears are more than what we just see on the outside, as we'll learn in a moment.

We use our ears to hear sounds when an object, like the string or my ukulele just now, when an object vibrates, so the string vibrates, but for me to hear it, for me to hear it, that sound, that sound and that vibration needs to travel from the vibrating string through the air, the air is the medium in this case, it needs to travel through the air to my ears, and then I can hear it, and that's the same whether you are playing the piano or making a sound in another way, something is vibrating, and that sound, those sound vibrations must travel to your ear.

All right, just to go back over what we've learned so far, let's hear some statements, and you can say which one you think is true and which one you think is false.

I'll read them to you, and you can show which one you think is true by making a T sign for true, or you could make an X sign for false, and you can do that with your arms just as easily as with your fingers.

So here it goes.

First statement, statement a, vibrations travel from the object through a medium to the ear.

Statement b, vibrations travel from the object through the ear to a medium.

Statement c, vibrations travel from the ear to the object through a medium.

Should we see which one was the correct one, which one was true? That's right, it was the first one, statement a, vibrations travel from the object through a medium to the ear.

So just to recap with my ukulele, once again, the vibration travels, (ukulele string resonating) I think I need to tune this, the vibration travels from the object, (ukulele string resonating) that's the vibrating string of the ukulele, through a medium, which is the air to the ear.

So let's return to one of those words, one of those keywords that we mentioned at the start, the word medium.

I'm gonna read you two children's definitions, what they think the word medium means.

And the first one is from Jun, and the second one is from Andeep.

And I would like you to put your hand up when you think I'm reading the one that is the correct one, okay? Here it goes.

So Jun says, "Sounds travel through a medium.

This is something not too big and not too small." And Andeep says, "Sounds travel through a medium, this means something for sounds to travel through, like the air." I hope you remembered which of the two was correct.

That's right.

Andeep was correct.

Sounds travel through a medium, and this means something for sounds to travel through, like the air.

Remember, though, it can be a solid medium, a liquid medium, or a gas medium.

How is it then that sound vibrations can travel in air from an object to our ears? Jun and Andeep have had some thoughts, and I'll read their thoughts to you in a moment, but I'd also like you to concentrate on what you think, what do you think about how sound is able to travel through the air from the object, like my ukulele string, to our ears? Jun says, "I think sound travels only to the person that hears it, like a laser beam, direct to a person's ears." Andeep says, "Oh, I think sound travels in all directions, to everywhere, and not just to the person who hears it." If you pause the video, you can tell your partner your idea.

Some ideas can be quite tricky to explain in words, can't they? Yes, "It's difficult to explain how vibrations travel from an object to our ears because we can't see them.

So I'm going to draw a diagram," Jun says.

He's gonna draw a diagram to help other people to understand what he thinks happens.

Scientists use diagrams to describe how things work or to explain things that can't be seen.

So draw a diagram to show how you think vibrations travel from an object to our ears.

Grab a piece of paper and a pencil when your teacher says, "It's okay." And then quickly draw a simple diagram to show your ideas.

You might use a mini whiteboard and a pen.

Off you go.

Pause the video now.

Gosh, that was a lot of busy diagram drawing.

Let's have a look at what Jun drew here.

So here's Jun's diagram, showing how he thinks sounds are heard.

"I think sound travels only to the person who hears it, direct to their ears." Can you see how Jun has shown that in his simple diagram? Does your diagram look like Jun's? Don't forget, it doesn't have to look like Jun's.

It's your ideas, your showing your own ideas.

Let's talk then about how those vibrations travel, and how then we are able to hear the sounds around us.

So when something makes a noise, like (claps hands) clapping your hands, or plucking a ukulele string, it creates vibrations in the air, and these vibrations travel in waves, sound waves spread out in all directions.

It's a bit like dropping a pebble in a pond, and that pebble creates ripples.

Have you ever seen a model quite like this? Can you see what it is? It's a model of our ear, and you can see inside the ear something called an eardrum.

So we're actually seeing our ear and then inside our ear, and that special part, what I just mentioned, is called a drum, an eardrum.

And when a sound wave reaches our eardrum, those waves make our eardrum vibrate.

And our brain, our brain is very clever, it's able to turn the vibrations into sounds, sounds that we recognise, sounds such as music or someone calling our name.

So let's just make sure that we understand this model.

I will draw around the bit of the ear that we can see on the outside of our heads, it's that part of the ear.

This is the side of our head here, and here, our head would continue like this.

And this part is called the ear canal, and that leads from our ear to the eardrum, which is here.

Time for a true or false.

So what do you think? Sounds travel in sound waves that we can see, true or false? Ah, but I don't just want you to say true or false.

I'd like you also to justify your answer.

I'd like you to say why you think your answer is either true or false, why you think it is, justify it, And that could be a, because sounds travel in waves, and these are invisible, or b, because sounds travel in waves, which we can only see at night.

Right.

Ready to come up with your answer? Pause the video now and decide which you think is the right answer and why.

Yes, it's false, sounds travel in sound waves that we can see is just not true, we can't see them, and they, we can't see them because they're invisible, they travel in waves, and these waves are invisible.

It's not that we can suddenly see them at night, they're invisible.

And if you want to show others, other people, your ideas about how vibrations travel in sound waves, what might be a really good way to do that? What do you think? Yes, that's right.

It can be a really good way to show people what your ideas are in a very clear way by drawing a diagram, a simple drawing to show your ideas.

Yes, so what better time, let's return to the diagram that we drew earlier, showing how vibrations from sounds travel to our ears.

Can you make some improvements to it? I'll tell you some things that you need to remember to include.

Make sure that you've included the object which is making the sound.

Make sure that you've shown the sound waves travelling to the ear.

And also, don't forget to include the person who hears the sound.

Off you go.

Work on your diagrams now.

Time to pause the video.

Well done.

You were very busy there.

What improvements did you make to your diagrams, I wonder? Well, here is the improvement that Jun made to his diagram.

He now knows that sound does not only travel to the person that hears it.

So if we look at the first drawing that he made with the yellow dog, you can see that in that drawing, in that diagram, the sound travels like a ball being thrown in, it just travels from the dog to the hero, to the listener.

In Jun's next diagram, his improved diagram, he's drawn something different.

Vibrations create sound waves that travel through the air in all directions.

We hear the sound when they reach our ears.

And Jun has shown this by, this is the one with the black dog, not the yellow dog, so now we see that the sound is, the sound waves are travelling outwards in all directions.

And because the listener is in range of that sound, she can hear the dog barking.

It's the last part of our lesson now, about the different mediums. And medium, remember, was that word that we came across at the very start of the lesson? Not meaning small and medium and large, but mediums, things that sound waves travel through.

Sound vibrations travel through a medium to our ears.

A medium can be a solid, a liquid, or a gas.

I wonder if you can think of some examples of solids, liquids, and gases.

There are three of them in the pictures below, we have wood, which is a solid, water, which is a liquid, and air, which is a gas.

Perhaps if you pause the video, you could think of some other examples.

So pause the video now.

Great thinking.

Sounds travel through different mediums. So Jun and Andeep have been talking about this.

Which explanation do you think is the correct one? Jun says, "Sounds travel through the same way, through all mediums, through vibrations." Andeep says, "Sounds can only travel through liquids and gases because solids are too tough for vibrations to travel through." Which of those two explanations do you think is the correct one? Yep, Jun has got it this time, he says that, "Sounds travel the same way through all mediums, through vibrations." Now, I'm going to read you three statements, and I want you to wave your arms in the air when I read the one that is correct.

So how do sounds travel through mediums to reach our ears? Is it a, through vibrations, b, some travel in straight lines, or c, sound only travels through air? I hope you were waving your arms on the first one because sound travels through mediums to our ears through vibrations.

Well done.

Here's something interesting, Izzy has been working with her synchronised swimming group on a new routine.

The group decide to play music through underwater speakers.

Do you think Izzy's group will be able to hear music through water? Wow.

This is what Izzy says, "We use the music to help us time when we do certain moves.

We can hear the music clearly underwater because water is a liquid, which is a medium for sound to travel through." So, yes, they can hear the music through the water.

I expect you'll all be dashing off to the swimming pool to try that.

Sound travels through all mediums by creating vibrations.

Imagine you play a musical instrument underwater, the instrument will cause vibrations in the water, which spread out in all directions.

If you're underwater, these vibrations travel through the water to reach your eardrums and make them vibrate too, causing you to hear the sound.

So, yes, sounds can travel through liquids.

And sound can travel through solids too.

Imagine bouncing a ball off a wall, the person on the other side of that wall can hear the sound.

The vibrations made by the bouncing ball travel through the solid medium of the wall and through the air to reach your eardrums, or the eardrums of your neighbour.

Sam has been thinking about how vibrations travel through different mediums. This is what she thinks.

See if you agree with her.

"Everything is made up of solids, liquids, and gases.

And that means that we can hear sound absolutely everywhere because there's always a medium for sound to pass through." Do you agree with her? And can you explain why? Pause the video for a moment and tell your partner what you think.

Some interesting ideas there, I'm sure.

Well, Sam's lucky because her neighbour is a scientist.

Sam asks her neighbour whether sound can always be heard.

Hmm.

Her neighbour thinks and replies, "Well, in space, there's no air, and, therefore, you cannot hear any sounds, as there's no medium for the vibrations to travel through." So, true or false? Sound cannot be heard in outer space? Oh, and don't forget to justify your answer.

You could say a, sound needs a medium to travel through, or b, outer space is too far away for us to hear sound.

What do you think? Take a moment.

Pause the video now.

Yes, it was true, sound can't be heard in outer space, it needs a medium to travel through.

Let's have a think about those mediums. Talk with a partner and decide which medium, solid, liquid, or gas, the vibrations are travelling through for each of these examples.

Are you ready? Here we go.

Listening to sounds in the room next door by holding a glass to the wall.

Hearing your friend shout to you across the playground.

Whales and dolphins communicating with each other by making clicking, whistling, and squeaking sounds.

Listening for a horse approaching by putting your ear to the ground.

Listening to music played through a swimming pool for a pool party.

I'll ask you to pause the video now, so you can just talk about this with your partner.

And we're back.

So what did you decide with your partner? Was it a solid, a liquid, or gas medium that the vibrations are travelling through in these examples? Listening to sounds in the room next door by holding a glass to the wall.

Well, both the wall and the glass are solids.

Hearing your friend shout to you across the playground, in that example, the air is a gas.

Whales and dolphins communicating with each other by making clicking, whistling, and squeaking sounds.

And the ocean is a liquid.

Listening for a horse approaching by putting your ear to the ground.

Yes, the ground is a solid.

And listening to music played through a swimming pool for a pool party.

Yes, the pool water is liquid.

Well done with those examples.

So it's time for us to sum up about how vibrations travel.

Sounds are heard when vibrations travel from the object through a medium to our ear.

We can use diagrams to show how sound waves travel.

A medium can be a solid, a liquid, or a gas, such as a wall, water, or the air.

Sound cannot be heard in outer space, as there is nowhere air, therefore, there's no medium for sound to travel through.

Well, that's it for today's lesson.

Thank you very much for working so hard.

Well done.

I'll see you next time.

Bye.