Hello, my name's Dr.

George, and this lesson is called "Magnetic poles." And if you don't know what those are, you will by the end.

And this lesson is part of the unit "Magnets and electromagnets." I hope you enjoy it.

The outcome for you to aim for by the end of the lesson is I can describe how magnets can attract magnetic materials as well as attract and repel other magnets.

Maybe you know something about this already, maybe you don't, but there'll be opportunities to experiment with magnets and find out how they behave.

Here are the keywords for the lesson.

I'm not going to go through them all now because I'll introduce them as we go along, but this slide is here so that you can come back and check the meanings any time.

There are three parts to this lesson.

North-seeking and south-seeking poles, attraction and repulsion, and magnetic materials.

Let's get started on the first part.

You may have seen or used a compass, and compass needles point towards north.

They're a way of finding our way somewhere.

It's very useful to have a map and a compass, then you know where you are and which way you need to turn to get to where you're going.

And this shows two different kinds of compass.

They look quite different but they work in very similar ways.

So the compass needle, which isn't actually the kind of needle that you sew with, is a moving part of the compass that can swing around.

And the compass needle is a magnet and it lines itself up in a north-south direction.

And the end of the magnetised needle that points north, points to the north on our Planet Earth, is called a north-seeking magnetic pole.

That's its full name.

And the other end is called a south-seeking magnetic pole.

Now a quick question for you.

Which of the following statements correctly describes the white end of the compass needle shown here? I'll wait five seconds, but if you need longer, press pause, and then press play when you're ready.

And the correct answer here, so this is a south-seeking pole.

The red end of the magnet with its arrow is the north-seeking pole, it points towards the North Pole on our planet.

The other end is south-seeking.

Now magnets are often labelled with N and S, as shown here, and people often just call these north pole and south pole, but the full name for the N end is it's a north-seeking pole.

And that means that if it can move freely, the magnet will swing around so that that north-seeking pole points towards our Earth's north, and the south-seeking pole will then point towards our Earth's south.

So another question.

Which of the following does a magnet have? Look carefully at all the options before you choose your answer.

I'll give you five seconds, but if you need longer, press pause, and press play when you're ready.

And the answer is A and B.

A magnet has a north-seeking pole and it also has a south-seeking pole.

It doesn't have a positive pole or a negative pole.

Those aren't real things.

And magnets can be found in different shapes and sizes, so not just these bar magnets that you might have experimented with yourself in science lessons.

You can also take a long bar magnet and bend it round into a horseshoe shape, and that still acts as a magnet.

And you can get magnets in the shapes of flat discs like these, and there are other shapes too.

So all of these magnets will have a north-seeking pole and a south-seeking pole, but the poles aren't always labelled on the magnet.

On these magnets, the north-seeking pole is as shown here and the south-seeking pole is here.

Another question to see if you're following along.

Which of the following statements is correct about the magnet pole shown? Choose one of those answers.

Pause the video if you need longer than five seconds, then press play.

And the correct answer is this is a south-seeking pole.

It's the pole that wants to point towards Earth's south.

Well done if you're getting these questions right.

Now imagine breaking a bar magnet in two.

You could perhaps snap it in two if you were strong enough or saw it into two pieces.

So we're going to break it here in the middle.

So we break it in the middle, so do we end up with a single north-seeking pole and a separate south-seeking pole? Turns out this is not what happens.

What we get is two new smaller magnets.

So the one at the top develops a south-seeking pole to pair with its north-seeking pole.

The one on the bottom gets a north-seeking pole to pair up with its south-seeking pole.

In fact, scientists haven't been able to discover or create a single north-seeking pole, a magnet that only has one type of pole or only has south-seeking pole.

They just don't seem to exist.

So magnets always have this pair of poles.

And another question.

Which of the following statements is correct about magnetic poles? And if you need more than five seconds, press pause.

And the correct answer here is all magnets have two poles.

I've just been telling you that scientists haven't been able to create or find a magnet that only has one type of pole.

Now Aisha and Jun are working with magnets and they've been told that this magnet will break in two if it's dropped, so they need to be careful when they're using it.

And they're thinking about that and Aisha says, "If the magnet breaks, it will lose its magnetism." But Jun says, "If the magnet breaks, there will be two pieces.

A single N pole and a single S pole." I'd like you to think about their statements and identify whether each of them is correct or incorrect and explain why.

And when you're finished, I'll show you some example answers.

So take as long as you need, pause the video, and press play when you have your answers ready.

Let's check the answers.

Jun's statement is incorrect.

He thinks that you'll get one magnet with just an N pole and one magnet with just an S pole.

But we've seen that if you break a magnet in half, you get two new magnets, each has a north-seeking and a south-seeking pole.

Aisha's partly correct, she says the magnet will lose its magnetism.

Now if she's thinking that happens because it breaks in two, that's not right.

But if she's thinking that it loses magnetism because it gets hit when it lands on the floor, she's partly right.

If a magnet is hit hard, it may lose some of its magnetism.

So you might not have known that, but if you are experimenting with magnets, be careful not to drop them.

Now let's look at part two of this lesson, attraction and repulsion.

A magnetic force is a non-contact force.

Now remember, each type of force can be categorised as being a contact force or a non-contact force.

Contact forces happen only when things are touching each other.

For example, friction.

Friction happens between two objects if they're rubbing against each other.

It can't happen at a distance.

Non-contact forces, such as gravitational forces, can act at a distance, and magnetic force is one of those.

Here we can see there's a force between the magnet and the paperclip even though they're not touching.

The paperclip is attached to a thread which is stuck to the desk with tape, and the magnet is pulling on the paperclip and making it hang in the air.

So the magnet and the paperclip are attracting each other.

So attractive forces are forces that pull things towards each other.

It's fun to try out this little demonstration if you have the right equipment.

A magnetic force can also act when things are touching.

So although it's a non-contact force, it can still happen when there is contact.

So this magnet is attracting some paperclips that are touching it.

But notice also now that some of these paperclips aren't touching the magnet but they are attracted to other paperclips, they want to stick to the paperclips that have stuck to the magnet.

And magnetic force can act through some materials.

Here we have a piece of card between the magnet and the paperclip.

It doesn't block the magnetic force, they're still attracting each other.

And that's another thing that you could investigate if you have the chance, trying different materials and different thicknesses to see what might block a magnetic force.

And here's a question.

Read the three statements carefully and decide which one is correct.

Pause the video if you need longer than five seconds.

Are you ready? The correct answer is some objects become magnets when they are in contact with a magnet.

How would you know that? Well, you saw paperclips sticking to paperclips that were stuck to a magnet.

So when a paperclip is stuck to a magnet, the paperclip itself behaves like a magnet and it can attract another paperclip.

It can be fun to try seeing how many paperclips you can stick to a magnet and whether you can get 'em to stick in a long line hanging down from the magnet.

The other two statements here aren't true.

And now a little experiment for you.

You'll need two bar magnets and also an iron nail.

And I'd like you to test these combinations, these pairs of objects, in the ways that are shown here.

You move each pair close together and you observe what happens.

Can you feel them attracting each other or can you feel something else? So take as long as you need, pause the video, and press play when you're ready.

Now let's check what happens.

With N and S facing each other, you get attraction, they try to pull each other together.

But if you have N and N facing each other, or S and S facing each other, you should have noticed the opposite of attraction, repulsion.

You should have noticed the magnets pushing each other away.

And with the iron nail you should find it doesn't matter which side you put the iron nail or which way the nail is facing, it's always attracted to the magnet.

If your nail was repelled by the magnet at all, that would mean that your nail was a magnet too, and it would mean that somebody before you had turned the nail into a magnet.

But an ordinary iron nail should only ever be attracted to a magnet.

Let's go to the last part of this lesson, all about magnetic materials.

As you've seen, magnets attract and repel other magnets depending on which way they're facing.

Unlike poles of magnets attract.

We're using the word unlike to mean the poles that are not the same.

North-facing, south-facing.

And like poles, poles of the same type, repel.

North-facing repels north-facing, south-facing repels south-facing, so we get repulsion.

But the iron nail is only attracted to the magnet whichever way we turn it and whichever pole it's facing.

And that's because iron is a magnetic material, and objects made of magnetic material are attracted to magnets.

Now an object made of magnetic material can be made into a magnet.

It's possible to take a piece of iron and make it into a magnet.

But ordinary pieces of magnetic material are not usually magnets, they're just attracted to magnets.

Now at the beginning of the lesson we looked at compasses and the way that their north pole is attracted to the North Pole of the Earth, and that's because Earth behaves as if there's a giant magnet inside it.

And the north-seeking ends of compasses are attracted to what we normally call the North Pole of the Earth, what you would see as the North Pole on a map.

But that means that up there there is a self-seeking magnetic pole.

So close to the Earth's geographic North Pole, what you would call the North Pole in geography, there is a south-seeking magnetic pole.

Now the Earth doesn't really have a giant bar magnet inside it, but it does behave almost as if it does.

And that's because the Earth really is magnetic.

I'm not going to go into the details of why, except to say that it's to do with the fact that the Earth's core, the centre of the Earth, is made of liquid iron.

Now here are four statements and I'd like you to think about which of the statements are correct.

Press pause if you need longer than five seconds to think.

And the first statement is true.

N attracts magnetic materials and S attracts magnetic materials.

Both poles of this magnet would attract an iron nail, for example.

It's also true that N attracts the S of another magnet, unlike poles attract, and N repels the N of another magnet, like poles repel.

The other two statements aren't correct.

They talk about the ends of the magnet being positively or negatively charged.

That's not what's going on.

Now here's a periodic table, or most of a periodic table.

It shows elements that the universe is made of.

And out of all these elements, only three are magnetic materials, and that's the metals iron, cobalt, and nickel found here in the table.

Iron is a very well-known metal, but cobalt and nickel, not so well known.

But it's just these three that are magnetic, none of the other elements are magnetic materials, they wouldn't be attracted to a magnet.

Another magnetic material is steel.

Steel's not an element, so you wouldn't find it in the periodic table.

It's a mixture.

It's made of mostly iron with small amounts of carbon and other elements mixed in.

And it's magnetic because it's mostly made of iron.

Another magnetic material is magnetite.

This is something that occurs naturally, you can dig it up out of the ground.

It's a compound of iron and oxygen.

And sometimes, if you dig up or if you find some magnetite, sometimes it actually behaves like a magnet, just naturally.

And when it does, it's called lodestone.

And people discovered this a long time ago, many centuries ago.

And even now we're not quite sure why some pieces of magnetite are actually magnets.

Scientists think it might have something to do with lightning strikes.

Lodestone was first written about, as far as we know, by the Greek Thales of Miletus back in the 6th century BC.

Which of the following statements are correct? Consider each one.

Press pause if you need longer than five seconds and play when you're ready.

B is correct.

All non-metal elements are not magnetic.

None of those magnetic elements were non-metals.

They're all metals.

Lots of metal elements are not magnetic, that's true.

There's only three that are magnetic, and there are many other metals, none of them are magnetic.

The first statement is not true but it's something that people commonly get wrong.

All metal elements are not magnetic, only three of them.

Well done if you got that correct.

Now let's compare magnetic forces and electrostatic forces.

I'll remind you of what those are.

So here's an example of magnetic forces, unlike poles, attracting.

And here we have two balloons that are charged.

The one on the left is negatively charged, the one on the right is positively charged.

And unlike charges attract as well, so a negatively-charged object and a positively-charged object attract each other.

And that's electrostatic forces.

Now we also know, of course, that like poles repel.

And with electrostatic forces, we see them repelling with like charges.

So positive balloon repels positive balloon, negative balloon repels negative balloons.

So we can see the similarity.

But we have to be careful because although magnetic forces and electrostatic forces have similarities, they are different types of force, they're not the same thing.

And if you had a magnet and you put one or two charged balloons next to it, there were no forces between the magnet and the balloons.

The magnet and the balloons are not interested in each other because N and S poles and positive and negative charges are different things, and magnetic forces and electrostatic forces are different types of force.

Here's a true or false question for you.

Non-metals are magnetic if they have an electric charge.

Is that true or false? And then pick a reason to justify the answer you chose.

Pause the video if you need more than five seconds.

And the answer is it's false.

Whether or not something is magnetic is a completely different thing from whether it has an electric charge, positive or negative.

So the reason that this is false is magnetic and electrostatic forces are different.

Now a final task for you, it's a puzzle.

You have three mystery blocks.

They're all painted so that they look identical, but they're not.

One of them is iron, one is copper, and one is a magnet.

And you also have a magnet, as shown.

I'd like you to explain how you would use the magnet to identify which block is iron, which is copper, and which is the magnet.

Take as long as you need, press pause, and when you're ready, press play.

Now let's look at an example answer.

It says, "First bring the S pole of the magnet close to a block and note what happens.

Then do the same thing with the N pole of the magnet.

If there is no attraction with either the S or N pole, it is copper.

If there is attraction with both the S and N pole, it is iron.

If there is attraction with one pole and repulsion with the other, it is another magnet." Now you don't have to have written your answer exactly in that order, but did you use your knowledge that copper is not magnetic so it won't be attracted to the magnet at all, iron is a magnetic material, so it will be attracted to both ends of the magnet, and the other magnet will attract or repel depending on whether you have like poles or unlike poles facing each other.

So well done if you got that.

Now we're at the end of the lesson, so let's look at a summary of what it was all about.

All magnets have a north-seeking pole and a south-seeking pole, and a single pole cannot exist on its own.

Earth has a magnetic field that causes magnets to align in a north-south direction.

Like magnetic poles will repel, and unlike poles attract.

Iron, cobalt, and nickel are the only three elements that are magnetic.

Alloys and compounds of these are sometimes also magnetic.

Steel is an alloy, a mixture of iron that contains carbon, and is magnetic.

Well done for working your way through this lesson.

I hope you've enjoyed it and learned a thing or two about magnets, and I hope to see you again in a future lesson.

Bye for now.