Lesson video

Hi there.

I'm Miss Roberts and I'm here today to take you through another geography lesson from our unit of work all about what shapes life at the coast.

Today, we are going to be thinking about waves and tides and the effect that they have on our coastline.

By the end of the lesson today, you will be able to explain what waves and tides are.

You will also be able to identify and describe different types of waves.

Let's have a look at some important geographical terms that you are going to hear in the lesson today.

I would really like you to be able to use these words yourself in your work as well.

Our first word is what this lesson is all about, and that's waves.

Quite simply, waves are the movement of energy across water.

Tides.

Tides are a rise and fall of sea level, and this happens very regularly, and it's actually caused by gravity.

We're gonna see some more about that later on.

Wind is the natural movement of air.

I'm sure we're all familiar with what it feels like on a windy day.

Our final keyword for today is fetch.

You may have heard that word as a verb before, to fetch something.

But in this case, it's not a verb, it's the name for a distance, and the distance is the distance across a body of water that a wind can blow.

The fetch is important in our context today because the fetch affects the size of waves.

We are going to have two parts to this lesson.

First, we need to find out what waves and tides are.

Then, later, we're going to think about whether or not all waves are the same.

So let's make a start now and look in some more detail at waves and tides.

The reason that we are looking at waves and tides is because the waves and tides of our seas and our oceans help to shape our coastlines.

You can see some very choppy water in this photograph where there are waves.

Waves are created when wind blows across the sea or an ocean.

The wind gives the sea water the power or the energy that it needs to move instead of remaining calm and still.

That movement, that energy, is seen visibly as waves.

You will be able to recognise here where the water is rising and you can see some white water there as well.

These are all visible signs of waves.

Before we move on, let's just check what we know so far.

Were you paying attention, and can you tell me what creates waves in the sea? Is it the sun, is it the tides, or is it the wind? Make your choice now.

It's the wind.

The wind is what creates waves because that's where waves get the energy from to move.

So what we are saying essentially is that waves can only happen when there is wind to power them.

If there's no wind, then there's no waves, there's no movement at all.

The movement of water through waves is not the only movement that our seas and oceans experience.

This is because we also have regular, predictable patterns of movement that are known as tides.

Tides happen twice a day, every day, every 12 hours, in fact.

Whether there is wind or not, tides will still happen.

The level of the sea or the ocean will still rise and fall on a regular 12-hourly basis.

Lucas says that when he was on holiday, he was asked to leave the beach because the tide was coming in.

Lucas is wondering what that actually means.

So let's find out.

Tides are changes in the level of the oceans or the seas, and this is actually caused by gravity, by something called gravitational pull.

You can see the apples here falling from the tree.

This represents what gravity does.

Gravity is a force.

You may have heard of gravity from your science lessons.

Gravity is the force that makes things fall to the floor on Earth.

So these apples will fall to the floor, or in fact, be pulled to the floor, by the force of gravity.

That's what's happening to the water in our seas and in our oceans, but that gravitational pull is actually coming from outer space.

Before we think some more about that force, let's stop and have a quick think about what we know so far.

Is this statement true or false? Tides are caused by the wind blowing over the sea or an ocean.

Think carefully, and make your choice.

Ready? This statement is actually false.

Can you say why it is false? Wind blowing over the sea is what results in waves.

Wind gives the water the energy to make them move, which creates the waves.

That is not the same as tides.

Tides are created by gravitational pull.

We're going to look some more at this now.

And it's that gravity that creates the tides.

We don't rely on wind for tides.

Here you can see planet Earth.

Planet Earth is constantly rotating on its axis.

We are spinning round.

The Moon orbits planet Earth.

It goes around us, and the Moon itself is also constantly rotating.

As the Moon orbits Earth, it exerts what we call gravitational pull.

That means that the water in our seas and oceans is attracted towards the Moon.

It pulls the water towards it.

This causes the sea level to rise in the places on Earth that are closest to the Moon at any point in time, and that's what we call the tide.

When that water is pulled closer to the Moon and the sea level rises, that is high tide.

High tide is when the sea level is at its greatest.

The water comes all the way into the shore, and it covers the beach and covers the shorelines.

This is when we can see the water there.

The opposite is, of course, low tide.

Low tide is when the sea level is at its lowest.

So this is when it's furthest from the Moon.

Beaches, estuaries, other coastal areas that would be below the water are all revealed at low tide.

You can see here all of these boats can't go anywhere until the tide comes back in and they have water to float on.

Lucas may have been sat on a beach at low tide, and as the tide reached high tide, then they would be asked to leave for safety.

So here are two photographs.

Look at them carefully and decide which of these you think shows a coastal location at high tide.

I'd also like you to think about how you know this.

Why have you made your choice? You can pause the video now, and you may want to talk to a partner about things you can see in each photograph.

Have you made a decision? Excellent.

Photograph A is the photograph that shows a coastal location at high tide, and we know this because the water has completely covered that beach or harbour, whatever happens to be there, the water is completely covering it.

We can't see any beach, we can't see any boats.

Whereas in photograph B, there is a large beach which is visible and we can see patches and puddles that have left some water behind as the tide has gone out.

Well done.

You've heard a lot of information about winds and tides there, so let's put that new learning to use and complete an activity together.

I would like you to think about ways in which waves and tides are similar, but also how they are different.

I would like you to make some notes in a table like this one.

You don't have to write in complete sentences, but I want you to think very carefully about how they are similar and how they are different.

Pause the video now whilst you complete the activity, and if you finish this quickly, perhaps you could share your ideas with a partner and compare how you both answered.

Finished.

Good job.

I've got an example table to share here with you now with some notes in.

Let's start with similarities.

I think the most obvious similarity is that waves and tides are both things that happen in the sea or in the ocean at the coast.

They happen in the same location.

Both of these things involve seawater, and in fact, both involve moving seawater.

So they're both to do with water from our seas and oceans moving in some way.

And both of these movements of seawater help to shape our coastlines.

The differences I've got on this table are that tides have regular patterns, whereas waves don't.

Waves can only happen if there's wind, whereas tides, being caused by gravitational pull, are happening on a regular basis.

Waves are only caused when the wind blows over the sea.

Did you have similar notes in your table? Good job.

Okay, so let's move into the second part of today's lesson.

We're gonna think in some more detail about waves now, and we're going to consider whether all waves are the same.

Waves can actually be many different sizes.

They could be very, very small and gentle waves, ripples, or they could be extremely large waves.

You may have heard of something called a tidal wave, which is a huge wave.

Why are waves so many different sizes, though? What determines that? The main factor that contributes to the size of a wave is the strength of the wind that powers it, that makes it, and the distance that that wave has travelled across water before it reaches the shore.

In some places that regularly experience big waves, they can be used by people for leisure activities like surfing.

You can see some people surfing the waves in this photograph.

Waves can travel for great distances along stretches of open water.

Think about how vast our oceans are, how big our seas are.

Waves could travel across the entire expanse of an open body of water.

That distance that a wave can travel as it blows across the water is called the fetch.

Yes, that's the keyword we mentioned earlier, the fetch.

Okay? The fetch is this distance that a wave travels.

And the idea here is that the greater the fetch, the bigger the wave will be.

So the further a wave has travelled, the bigger it gets.

Take a look at this simplified diagram here.

You can see the direction of the wind is labelled, and you can see the water moving in that same direction.

We have some very small ripples close to the shore, so there's very little movement there because the distance from the shore isn't that great.

However, follow those ripples along and notice that the waves begin to get bigger and bigger and bigger.

And why is that? That is because the distance from the shore is getting bigger too.

The greater the fetch, the bigger a wave will be.

Okay.

Thinking of what you now know, what term describes the distance that a wave travels across open water? Is it A, the stretch; B, the fetch; or C, the tide? Make your choice now.

Got it? It's the fetch.

Well done.

That's our keyword, isn't it? Fetch.

Waves can travel for great distances across these stretches of open water, but they can't continue to just keep travelling and travelling and travelling.

They have to stop somewhere.

They often stop in areas of shallow water.

They break onto beaches.

We can see white water here, which is something we see very often on shorelines where waves are breaking.

It means that waves are washing up, waves are stopping there, and we see this white water.

When a wave breaks on a beach, the water that is pushed up the beach is called the swash.

The water that runs back down the beach is called the backwash.

You can see the swash and the backwash here in this clip on a beach in Hawaii.

The swash breaks onto the beach and runs up, and the backwash runs straight back down.

You can also see the white water of the wave as it breaks on the shore.

So let's put your new knowledge into practise.

I would like you to write a short, just very short, single-sentence description, of each of these terms which we have already used.

I want you to write a description of waves, of swash, and of backwash.

You can pause the video now whilst you do this.

Ready? Okay, I'm going to share some example descriptions with you now.

Let's see how similar your ideas are to these.

Waves are the movement of seawater caused by wind.

Swash is seawater running up a beach toward the land.

And backwash is seawater running down a beach toward the sea.

Well done.

So now we know what happens when waves travel across water.

We know what causes them to be different sizes, and we've seen what happens when waves break onto the shore.

But do they all behave in the same way? Are waves always doing the same things? Let's find out.

There are two different categories or types of wave: destructive waves and constructive waves.

Destructive waves have a very strong backwash but a weaker swash, and they can reduce beaches because of the erosion that they cause.

In contrast to this, constructive waves have a very strong swash and a weaker backwash, and these are the types of waves that can help to build up beaches through deposition.

The two diagrams and the arrows show the processes of the waves breaking.

You can see how the destructive wave scoops up material as it erodes it, and you can see how the constructive wave pushes material up the beach.

So do you think this is true or false? Destructive waves have a very strong swash.

Is that correct? That is false.

And can we say why it is false? It's false because constructive waves have a very strong swash.

Destructive waves have a very strong backwash.

Well done.

So let's take everything we now know about the size of waves and the types of waves and use that knowledge to do an activity together.

Here you can see two maps of the South Coast of England, and on those maps, A and B are labelled.

They represent the paths of two different winds.

They're both travelling towards Brighton on the South Coast.

I would like you to think about which of those, A and B, do you think will generate the largest waves at Brighton? Which of those do you think is going to create the largest waves in that location? I would also like you to explain why you've made that choice.

Pause the video now to complete the activity, and then I will share some example answers with you.

Good luck.

Ready? Okay, let's look at this example answer together now.

Now, the decision that's been made here is A, and the main reason is that A has a greater fetch.

The fetch is the distance, isn't it? And the fetch of A is up to 8,000 kilometres that that wave has travelled, whereas the fetch of wind B, those waves have only travelled 200 kilometres.

The explanation that's given here says that the size of a wave varies depending on the distance the wind has blown it across open water.

This is known as the fetch.

The greater the fetch, the larger the waves will be.

Wind A has travelled over 8,000 kilometres, and wind B has travelled less than 200 kilometres.

The fetch of wind A is greater than wind B, so A will generate the biggest waves.

Was your explanation similar? Great work.

You've listened very well to lots of geographical information today, so let's just review everything we now know.

We know that waves are powered by the wind, whereas tides are controlled by gravitational pull between the Moon, the Sun, and Earth.

We know that the stretch of open water over which the wind blows a wave is called the fetch.

We also know that there are different types of waves.

Constructive waves have a powerful swash with a weak backwash, and destructive waves have a powerful backwash and a weak swash.

I hope you have found it interesting to discover how seawater moves in the form of waves and tides and how that all comes about.

Join me again for our next lesson in this unit to discover more about what shapes life at the coast.

Bye for now.