Hello, everyone.

It's lovely to be learning science with you today.

I'm Dr.

Pemberton, and I'm really looking forward to working through the lesson, so let's get going.

Today's lesson is an introduction to gravity.

Gravity is something that's really important in all of our lives.

It may be something you already know a bit about, or it may be completely new to you.

The learning outcome for today is that you can explain why unsupported objects fall towards Earth.

It's part of our big question, how do forces make things happen? I'm looking forward to working as a scientist with you today and to learn more about gravity.

I hope you are too.

These are the keywords that we'll be using in today's lesson.

Earth, force, pull, gravity, and unsupported.

Some of these words may be new today, but I'd have thought other words may be familiar to you already.

This slide shows the meaning of the keywords.

I will explain each of these words as we come across them during the lesson, so we won't spend time going through each one now.

It's just here as a reminder, and you might like to come back to it later to check that you're confident using the words.

This is our lesson outline for today.

There are two parts to the lesson.

We'll begin by learning about forces and gravity.

Then we'll consider the discovery of gravity, where we'll learn about the history of how gravity has been described and explained by different scientists.

We're going to get going on the first part of our lesson now, forces and gravity.

We hear the word "force" in our everyday lives quite often.

We talk about the force of your foot on the pedal when you ride a bike.

We talk about the force of the bat on the ball in sports like baseball or cricket or rounders.

Do you know what a force is? A force is a push or a pull.

Contact forces occur where objects push or pull when they're touching each other, just like in this picture where we can see someone pushing a door by touching it or making contact with it with their hand.

Non-contact forces occur where objects push or pull when they're not touching each other.

We can see here in this great picture of what looks like a paperclip floating in the air, but it's actually a paperclip being attracted to a magnet which is not in contact with it.

Magnetic force is a non-contact force.

If you let go of something you are holding, it becomes unsupported.

That means nothing is holding or supporting it.

In this picture, I was about to let go of the mug.

What happens when you let go of something? That's right, it falls downwards.

But why is that? Is there a force pushing or pulling on it? Well, when you let go of something, the object falls down due to an invisible force which is pulling it down.

Do you know what this force is called? It's gravity.

Gravity is a non-contact force that makes unsupported objects fall towards Earth.

Let's check what we've learned so far by trying a couple of questions.

The children in this slide are discussing what will happen if they let go of a book so it becomes unsupported.

Who's correct? Let's see what each of them thinks.

We'll start with Jun and then move around clockwise.

Jun thinks it will stay where it is.

Izzy thinks the book will be pushed up in the air by gravity.

Andeep thinks it will be pulled down to Earth by gravity.

And Jacob thinks it will be pushed down to Earth by gravity.

Who do you think is correct? Well done if you agreed with Andeep.

He's right.

An unsupported book will be pulled down to Earth by gravity.

Gravity's a pull, not a push.

Let's try another one.

Which of these pictures show non-contact forces? Is it A, a magnetic force attracting a paperclip, B, a drawer being pulled open, or C, a leaf falling to the ground? That's right, two of these are non-contact forces.

A, the magnetic force attracting the paperclip and C, the leaf falling to the ground.

Now it's your turn to do some science.

This is your first science challenge for the day.

You're going to try some activities to help you explore gravity.

Some of these are things you will have seen or tried before, but I wonder if you realised that gravity was causing them.

Let's look at the first one.

Attach a piece of paper to an easel or the wall, or if there aren't easels or enough space on the wall, do this with a friend.

One of you needs to hold the paper upright, and the other one needs to put a blob of paint at the top of the paper, and then see what happens.

It might be a good idea to put the blob of paint on the paper before you pick it up, then hold it upright.

What do you expect to happen? When you try it, discuss these things.

What do you notice about the direction the paint runs? What happens if you turn the paper a different way up? And finally discuss why do you think this happens? Why do you think the paint moves in the way it does? Your second challenge is a bit more energetic.

If you can find a safe, clear space to do so, try a handstand or a cartwheel.

What happens to your hair? You might have to ask a friend to tell you 'cause you can't see your own hair when you're upside down.

Why do you think that happens? Finally, you've got one more challenge in this task.

For this one, you need to throw a ball up in the air.

How long does it stay there? You could count while it's up in the air.

How long can you get it to stay? Is there any way you can throw it to make it stay in the air longer? Why doesn't it stay any longer? It's time for you to pause the video and try the tasks.

When you've finished, come and rejoin me for the next part of the lesson.

Welcome back.

How did you get on, and what did you find? You might have found something like this.

First, what about the paint task? Here's what one child said, "The paint always ran towards the floor, whichever way up the paper was.

This was because gravity was pulling it down." Did you find something like that? Did you think that was why it was happening? How did you get on with the ball? How long could you get it to stay in the air for? The child here said, "The ball stayed in the air for two seconds.

After that, it came down again because of the force of gravity." Finally, the cartwheel.

This child said, "When I did a cartwheel, my hair all fell downwards, covering my face.

Gravity was pulling it down." Great, so we've already learned that lots of interesting things we see in our day-to-day lives can be explained by gravity.

I wonder how long people have known that it's gravity that makes our hair fall down if we're upside down, or that it's gravity that makes paint run down the wall, or that it's gravity that makes balls return to Earth.

We're going to find out in our next section.

Our second section today is called "The discovery of gravity." Now, gravity's always existed.

What we mean by the title is that we're going to find out how scientists learned and explained what gravity is.

For many years, people realised that there was a force that pulled them towards the ground.

That's why unsupported objects fall down.

And if we didn't have gravity, we'd all float around in the air.

It's gravity that keeps our feet on the ground, literally.

Now, Aristotle was a famous Greek thinker.

We can see a photograph of a statue of Aristotle here, and it looks to me like he's thinking in this picture.

He might be writing as well as thinking.

Aristotle thought that Earth was the centre of the universe, which was why objects were attracted to it.

He also thought that the heavier the object, the faster it would fall to Earth.

So Aristotle made a good start of explaining gravity.

He knew that objects were attracted to Earth, but he hadn't got everything right.

Over 1,500 years later, in 1589, Galileo Galilei, who was an Italian scientist, studied this pulling force that Aristotle had worked on.

He dropped two steel balls the same size, but different masses, from the top of the Tower of Pisa at the same time.

Now, the Tower of Pisa is a very famous building in Italy which is 57 metres high.

When I stand up, I'm just over 1/2 metres tall, so the Tower of Pisa is a very long way for a ball to fall.

Aristotle dropped these two balls, which weighed different amounts but were identical shape and size, and he dropped them at the same time.

Most people predicted that the heavier ball would hit the ground before the lighter ball.

What do you think? Galileo amazed everyone by demonstrating that the balls fell at the same speed and hit the ground at the same time.

This is because the ground pulls on every object at the same rate.

Gravity causes objects of the same shape, but different mass, to fall at the same speed.

The next person to study gravity was Isaac Newton.

In 1667, Isaac Newton, who was a British scientist and astronomer, built on Galileo's work and gave us the word "gravity." It hadn't been called that before he gave it that name.

According to stories, while sitting under a tree, Isaac Newton was hit on the head by a falling apple.

Newton wondered why the apple had fallen straight down rather than sideways, and he realised that everything falls straight down.

Newton realised that the Earth must have a force in its centre that pulls things straight down.

He actually worked out that all objects pull other objects, and he called this pull gravity.

Newton also worked out that big objects, like planets, have stronger, more obvious gravitational pull than small objects, like people.

So, that's the history of how different scientists have tried to explain gravity.

Let's see what you can remember with a couple of questions.

Here's the first one.

Why did the balls dropped by Galileo fall to the Earth at the same speed even though one was heavier? Was it A, because the wind blew the lighter one so it could keep up with the heavier one, or B, because Galileo used more force when he dropped the lighter ball, or was it C, because objects of the same shape, but different mass, fall at the same speed? That's right.

It was C.

The balls that Galileo dropped to Earth fell at the same speed, even though one was heavier, because objects of the same shape, but different mass, fall at the same speed.

Let's try another one.

According to historical stories, what made Newton start thinking about gravity? We've got four choices.

Was it A, eating an apple, B, an apple falling, C, growing an apple, or D, doing experiments with an apple? What do you think? That's right, according to stories, Isaac Newton started to think about gravity after an apple fell on his head.

I wonder if you'll remember that next time you eat an apple.

I think I will.

Perhaps you could tell someone else about it when you see them eating an apple.

Now it's time for you to do some more science.

You are going to recreate Galileo's experiments.

No, you're not going to the Tower of Pisa.

You're going to recreate them wherever you are now.

The first thing you'll need to do is take two identical plastic or metal water bottles.

Fill one bottle completely with water, and only half fill the other one.

Which is heavier? You can probably feel it, but why don't you weigh them to find out their masses? It's always really good to practise our measuring because scientists are more accurate if they're good at measuring.

Which one of your bottles do you think will fall faster, and why do you think that? Your next step is to try it.

Drop both bottles from the same height at the same time onto a soft surface or outside.

Why do you think I'm suggesting a soft surface or outside? That's right, we don't want the bottles to break, and if they do split or leak, it will be a good idea to be outside.

When you drop them, check which one hits the floor first.

Why is that? Is it what you expected? Pause the video now, and go and try the experiment, and then come back and join me.

How did you get on? Did you find something like this? The half-full bottle weighed less than the full bottle, but both bottles hit the floor at the same time.

This is because they were the same shape, and Galileo said that objects of different masses, but the same shape, fall at the same speed.

Of course, that's why the bottles hit the ground at the same time.

Well, we're coming to the end of our lesson, but let's have a look at the summary to remind ourselves what we've learned.

Unsupported objects fall downwards due to gravity.

Gravity is an invisible force that makes unsupported objects fall towards the Earth.

And we've seen that throughout history, people have tried to explain this force.

We looked at Aristotle, Galileo, and Newton.

Galileo realised that gravity causes objects of the same shape, but different mass, to fall at the same speed.

Isaac Newton built on his work and realised that the Earth must have a force towards its centre that pulls things straight down.

Thank you for joining me this lesson.

It's been great fun learning about gravity together.

It's always fantastic to learn about things that help us understand the way our world works, and I love it when science can explain something that I've noticed in my day-to-day life, like my hair falling down when I do a handstand.

Well done for your hard work, and have a great day.

See you next time.