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 with you, so let's get going.

Today's lesson is called Friction: Plan.

We'll improve our understanding of friction, and we'll plan an investigation to learn more about it.

The learning outcome for today is that you can plan an investigation to measure the effects of friction.

It's part of our big question, how do forces make things happen? I'm looking forward to working with you and I'm looking forward to learning more about friction.

I hope you are too.

These are the keywords that we'll be using in today's lesson: surface, force, friction, and variables.

Do you know any of them already? This slide shows the meaning of each of the keywords.

It's just here as a reminder, and you might like to come back to the slide later to check that you understand how each of the keywords is used in a sentence.

I'll explain the words as we come to them in the lesson, so we won't spend time now going through each one.

This is our outline for today's lesson.

There are three parts.

The first part is learning how friction acts between surfaces.

Then we'll find out why scientists control variables in investigations.

And finally, we'll be planning to investigate friction.

We're gonna start now with friction acts between surfaces.

What is a surface? A surface is the top layer or outside of something.

Surfaces come in all different shapes and sizes.

Let's look at some surfaces.

The surface of the moon.

The peel is the surface of an apple.

And here we can see the surface of a wooden table.

Objects move differently over different surfaces.

Some surfaces are easy to move over, but others are difficult.

Which of these paths will be easier to move over? On the left is a dry path, and on the right is an icy path.

I think the dry path will be easier to move over because I can imagine slipping and having to tread really carefully on the icy path.

There's a force when surfaces move across each other.

What is this force called? Friction is the force between two surfaces that are moving or trying to move across each other.

When this ball rolls, the surface of the ball moves across the surface of the playground.

This creates friction forces between the two surfaces.

The friction's shown here in the white area where there's bits sticking out from the red and blue surfaces and they're getting in each other's way, slowing the moving object down.

Friction always works in opposition to the direction of the moving object.

It slows the moving object down.

In this picture, the sled is moving from left to right, in the direction shown by the red arrow, and friction acts in the opposite direction, shown by the grey arrow.

Without friction, moving objects would never slow down or stop moving.

Some surfaces have greater friction forces than others.

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

This is a missing word question.

I'll read out the sentence and say "blank" where the missing word should go.

Friction always works in the blank direction to the moving object.

Is the missing word A, opposite, B, same, or C, unrelated? Well done if you chose A.

Friction always works in the opposite direction to the moving object.

Let's try another one.

Which of these diagrams correctly shows how friction acts between two surfaces? That's right, it's B, where the friction is shown working in the opposite direction to the movement.

Remember, friction is the force between two surfaces that are moving or trying to move across each other.

Now it's time for your first task.

Friction is important in our everyday lives.

It occurs where two surfaces move over each other.

In the photo you can see someone skateboarding.

What two surfaces are moving over each other when you push forward to skateboard? Label the photograph to show the direction of the force of friction when you move forwards on the skateboard.

Pause the video now while you do this, then come and rejoin me to carry on with the lesson.

How did you get on? Let's look at part A.

What did you think were the two surfaces moving each other when you pushed forward on a skateboard? Here I've written, "The surface of the wheels moves over the surface of the floor." You might also have thought of the surface of your foot pushing off the floor.

And how did you get on labelling the photo? You should have added arrows pointing in the opposite direction to the movement of the skateboard.

Let's move on to the second part of our lesson.

In this section, we're learning why scientists control variables in investigations.

Scientists ask questions and plan investigations to compare two or more things.

They could use an investigation to compare the friction on different surfaces.

For example, they could compare how long it takes a toy car to roll one metre across different surfaces.

Here's Jacob, and he asked the question, "Do different surfaces affect the time it takes for a toy car to roll one metre?" To answer his question, Jacob plans an investigation as shown here.

He says, "We will let go of the car at the top of the ramp.

Then we'll measure the time taken for the car to travel the length of the ruler." We can see in the diagram that he is going to make his ramp using a book to prop up a plank.

At the bottom of the ramp next to the ruler, he's taped a strip of carpet as his first surface.

He's noticed that he'll swap the surfaces between each test.

What things could Jacob change each time he does his test? Well, there are lots of variables that could be changed each time Jacob does the investigation.

We call the things you could change variables.

One of the variables he could change is the toy car.

Can you think of any other variables? Some of the variables are the toy car, the surface at the bottom of the ramp, the height of the ramp, which is caused by the thickness of the books he's used.

For this test, the only variable that Jacob should change is the type of surface at the bottom of the ramp.

All the other variables must be controlled.

When we control variables, it means we keep them the same throughout our investigation.

This is to allow us to look at the effects of just one particular variable on a result.

So Jacob's question was, "Do different surfaces affect the time it takes for a toy car to roll one metre?" That means in Jacob's case, he controls all the variables except the type of surface because he wants to know if that affects the time it takes for the car to roll one metre.

It's time to see what we can remember with a couple of questions.

This is another missing word one, so I'll say "blank" where the missing word should go.

A blank is something that could be changed in an investigation.

That's right, a variable is something that could be changed in an investigation.

Let's try another one.

This is a multiple choice question.

Which of these questions could be answered by measuring variables in an investigation? Is it A, which surface is most expensive, B, which surface is the most popular, and C, which surface has the most grip? Which one do you think it is? That's right, it's B.

The others couldn't be answered with measurements.

Let's try one more.

How many variables should you control in an investigation? Is it A, all except one, B, one, or C, all of them? That's right, it's A.

We keep all except one the same when we carry out an investigation.

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

Andy and Izzy are discussing variables.

Andy says, "When you do a controlled investigation, you should only change one variable each time." But Izzy doesn't agree and she says, "When you do an investigation, you should control all but one variable each time." Your task is to talk to a partner about who you agree with and why.

Pause the video now while you do this, and then come back and rejoin me to carry on with the lesson.

What did you decide? Both of them are correct.

You change one variable just like Andy says, but you control all the others just like Izzy says.

To control a variable means you keep it the same, and we keep all of them the same except one.

Now we're going to move on to our third and final section today.

It's called planning to investigate friction.

Friction forces slow down moving objects just like this inline skater is slowed down by friction between their wheels and the tarmac.

Friction forces also make it harder to make a stationary object start moving.

The greater the friction force, the greater the force needed to make an object move.

We can control variables when we investigate the effects of friction.

Aisha has an inquiry question related to this.

She says, "Do different surfaces around my score affect the size of friction?" How could you investigate this? You could use a force metre to measure the force needed to move something over a surface.

That would give you a measure of the friction.

Would a high number of newtons mean low or high friction? High newtons means a lot of force is needed to move the object, so that means high friction.

Let's check what we can remember with some questions.

This is another missing word question.

I'll say "blank" where the missing word is.

The greater the friction force, the blank the force needed to make an object move.

That's right, the missing word is greater.

The greater the friction force, the greater the force needed to make an object move.

Did you get that? Let's try another one.

How would you interpret the measurements from a force metre in terms of friction? Do you think A, the higher the number of newtons measured, the greater the friction caused by the surface? Or do you think B, the lower the number of newtons measured, the greater the friction caused by the surface? That's right, it's A.

The higher the number of newtons measured, the greater the friction created by the surface.

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

You are going to plan an investigation to compare the amount of friction needed to pull a shoe over different surfaces, so you're going to try and answer Aisha's inquiry question.

First, you need to think about this, and then you'll need to discuss it.

It's always good to discuss our science before we start to wipe it down.

What will you do? Discuss that, and also discuss which variable you will change.

Which variables will you control? Remember, control means keep the same.

And also, what will you measure and how will you measure it? What equipment will you need? After you've talked about it, record your ideas with a labelled diagram and a list of numbered instructions for your method.

Then make a list of the variables and identify which one you'll change.

Pause the video now while you do this, then come and rejoin me to carry on with the lesson.

What did you decide to do? Perhaps your plan looked like this one.

Here we can see what Aisha has written.

"One, we will put a one kilogramme weight in a shoe and hook a force metre to the shoe." She's put a little star or asterisk next to the word shoe, and if I look at the star at the bottom of the page, it says, "We decided to add a weight to the shoe because without it, the force needed to move the shoe was too small to record on the metre." Ah, it was too easy without the weight, so they had to make the shoe heavier so a greater force was needed to move it.

That's clever.

Then number two, "We will put the shoe on the classroom floor and measure using the force metre how many newtons it takes for the shoe to move." Number three, "We will repeat this on other surfaces such as the carpet and the pavement." She's also done a diagram showing the shoe and how they'll set up the investigation with the weight in the shoe and the force metre pulling on it.

Was your plan like this or did you have a different idea? Perhaps you used a different type of surface to start with.

Well, we're coming to the end of our learning.

Let's look at our summary to remind ourselves what we have learned.

Friction is the force between two surfaces that are moving or trying to move over each other.

Friction always works in opposition to the direction of the moving object.

That means the opposite direction.

Variables are things that can be changed in an investigation.

An investigation should control all but one variable when attempting to answer a scientific question.

Only changing one variable allows us to know that no other variable has affected the results of the test.

Well, thank you for joining me this lesson.

I've really enjoyed learning about friction together, and I'd like to try out the investigation we planned.

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

See you next time.