Hello there, I'm Mr. Forbes, and welcome to this lesson from the Hidden Forces unit.

This lesson's all about levers.

And you may have seen some levers before.

But in it, we're gonna go into more depth about what makes up a lever and how they operate.

By the end of this lesson, you're going to be able to describe what the lever is and how it operates, identifying the key parts of it.

You'll be able to describe how we use them to generate larger forces.

To get the most out of the lesson, you'll need to understand these five keywords.

The first is lever, and that's what this lesson's all about.

We're going to see a range of levers and how they operate.

The second is to pivot, and that's the point on a lever about which it turns, so the turning point.

The effort is the effort force that you put onto a lever.

And the load is the force that the lever produces in order to move something usually.

And the final keyword is force multiplier.

And that's a type of lever that produces a larger load force than the effort force you put in.

And here's a list of those keywords again and their descriptions, so that you can return to it at any point during the lesson.

This lesson's in three parts.

And in the first part, we're going to recap what forces can do to objects and start to discuss the turning effects that they can generate, how they make objects rotate.

In the second part, we're gonna look at a wide range of levers trying to identify what they are and how they function.

And the third and final part, we'll start to discuss the relationship between the effort force you put onto a lever and the load force it generates, seeing what a force multiplier is.

So when you're ready, let's begin.

Okay, let's start the lesson by looking at what forces can do.

You've probably heard most of this information before, but this'll help you revise it.

So first of all, a force can change the motion of an object.

And by that, I mean that the force can make it speed up or slow down.

And you may well have carried out a wide range of experiments looking at the forces acting on objects, making them slow down, like friction, or speed up where you push or pull the object.

The second type of motion change that can happen is a change in direction of movement.

So forces can cause an object to change direction, such as when a car is travelling around the bend.

The next thing that forces can do is change the shape of an object.

And again, you might have tested forces acting on springs or elastic bands.

And you've seen those objects get larger or smaller, so the force can squash or stretch the object.

And the third thing the force can do to an object is make the object rotate.

We've not looked at that much yet.

And that's what this lesson's mostly about.

So let's have a look at some rotating objects.

Forces can have a turning effect on an object.

And that means the object rotates while it's in a fixed position.

So, for example, you could push on part of a door.

And pushing on that part of the door will cause it to rotate around its hinges.

So the door itself is still roughly where it was, but it's rotated in a different position now.

A better example is probably pushing a roundabout.

As you're pushing the roundabout, the roundabout spins, so it rotates, but it doesn't move from its fixed position in the ground.

So the force is just causing a turning effect.

There are no movement from one place to another at all.

When you're push or pull on a door, well, you're probably pushing or pulling on the handle.

And the handle is placed on the opposite side to where the hinges are.

So I've got a door here.

And if you look on the left hand side of the door, I've got a pair of hinges.

And the hinges hold the door in place and allow it to rotate.

On the other side, I've got the handle.

And it's as far away from the hinges as it possibly can be.

And the reason for that is if the handle was near to the hinge, it would make it much, much harder to open and close a door.

And you can try that yourself with a door.

If you've got a door and you want to close it, if you push near the hinges, you'll find it much more difficult to actually make it close.

You need a smaller force when you're a larger distance away from the turning point.

And that's typical of a lever.

Right, let's check if you understood about opening and closing doors.

A classroom door is open.

A pupil tries to close it.

Which of these three statements is correct? Is it more forces needed at point A? And you can see point A on a diagram there.

Or is it more forces needed at point B, which is also in the diagram? Or is it the same amount of forces needed at A as at B? So what I'd like you to do is to pause the video, make your choice, and restart.

(audio mutes) Okay, welcome back.

You should have chosen answer A, more forces needed at point A.

Point A is closer to the hinges on that door.

And therefore, you'll need a larger force to cause the door to close than you would if you were pushing a bit further away from the hinges, which is at point B.

So well done if you selected A there.

Now, when you wanna open most doors, you usually have to use the handle, because most doors have a latch that keeps them closed.

It stops the wind blowing them open, so you have to rotate a handle in order to open it.

A handle like this rotates around the what's called a spindle.

So it just rotates in place and allows the door to open.

As you can see here, I've got a long handle on this door.

And that's to allow me to increase the turning effect on it to make it open more easily.

If I try to open it towards the centre, it'd be very difficult to twist it round.

But if I just put my hand near the end, it's much, much easier.

Now, let's check if you understand how the handle operates.

I've got a door handle here.

And I've labelled it up with three different points, A, B, and C.

So to open this door, the handle needs to be rotated downwards, or anti-clockwise.

And I'd like you to identify which point shows where the largest force would be needed to open the door.

Is it point A, point B, or point C? So pause the video, make your choice, and then restart.

(audio mutes) Okay, welcome back.

Hopefully, you chose point C.

Point C is where the largest force would be needed because it's close to the centre of the handle, the turning point, or the pivot, as we'll see in a bit.

And you need a much larger force there than anywhere else.

Point A is the point where it'd be easiest to open the door.

Okay, it's time to check that you understand the turning effect of a force.

So I've got a figure here with two jars and with twist off lids.

Both of the lids are stuck on equally tight, so as tight as each other.

Which jar will need the largest force to twist the lid off? And I'd like you to try and come up with an explanation for your answer.

So if you look at the two jars there, X and Y, X has got a wider lid and Y has got a narrower lid.

So I'd like you to pause the video, answer that question, and then restart, please.

(audio mutes) Okay, welcome back.

Well, your answer should be something like this.

I've drawn the forces on the two jars, so we can discuss them more easily.

Jar Y will take the greatest force because the top of jar Y is much narrower.

It's got smaller diameter than jar X.

And that means I'm gonna need a larger force because I'm twisting closer to the centre of rotation on that jar.

Jar X is much easier to open because it's a much wider, larger diameter lid, so the forces don't need to be as large.

They're further away from the central point where the the lid will rotate.

So well done if you came up with those sorts of answers.

Okay, we're gonna move on to the second part of the lesson now.

And this is all about identifying levers.

In this part, we're gonna see a wide range of levers and try and identify the features that all levers have in common and the differences between them.

Some of the levers are easy to spot, while others aren't.

So the first thing that all levers have in common is a pivot point.

All levers need to have a pivot.

And a pivot is something that the lever can rotate around.

Now, there's a wide range of different pivots.

First of all, the pivot could be a set of hinges.

You've already seen a set of hinges on a doorframe.

And the door will rotate around those hinge points.

You can also have an axle or a spindle.

And when you turn a door handle, you get this rotation effect.

And that's moving around a spindle.

Or when a car wheel rotates, it's rotating around an axle.

So axles are rotation points, or pivots, as well.

And finally, it could be just a simple point.

So a seesaw could be a plank of wood that's resting on another one.

And it rocks back in two over that second plank.

And that would be a pivot point where those two planks meet.

The second thing required for a lever is the effort.

And the effort is a point where the force is applied to the lever to cause it to try to rotate.

So I've drawn a simple lever here.

It's got a pivot point.

And I've chosen to use just a simple seesaw type lever here.

And the pivot point's just a wedge there.

And that the effort can be a push or a pull applied to one end of the lever.

So I'm pushing down on this lever and I'm putting an effort on it.

And that effort would cause this lever to rotate.

On the other side of the lever is something called the load point.

And that point is where you place an object that you want to try and lift up.

So I put an effort on the lever, and it produces a load force.

So as we've seen, the simplest lever is just something like a solid bar.

So I've got a solid metal rod here.

And beneath it, I can place a pivot, which is a simple wedge there.

And I put an effort force on it.

I push downwards on one side of the lever, or I could be pulling up on that side of the lever instead.

And that will produce a rotation effect.

So this lever would start to rotate around that pivot point.

And if there was just the effort force here, that would rotate that end of the lever downwards.

So we could say this lever would rotate anti-clockwise.

But as it does so, it produces an upward force on the other end of the lever.

And that's the load point.

So you get an overall structure of the simplest lever that looks like that, a pivot in the middle, an effort on one side, and a load force on the other side.

There are actually three different types of lever.

And they're classified by where the effort force and the load force are in relation to the pivot.

So the first type of lever we've already seen.

I've got a pivot that's in between the effort force and the load force.

So I've got the effort force shown as the downward red arrow here, and the load force as the upwards green arrow.

And that's the type of lever we've seen.

It's something that you can use to lift objects.

The second type of lever has a load force that's in between the effort force and the pivot.

So again, you can see the effort force is upwards here, the load force is downwards, but the pivot's on one end of the lever.

An example of that is a wheelbarrow.

And we'll have a look in a bit more detail at a wheelbarrow later.

But that's the second type of lever.

And the third type of lever, as you might have guessed, has the load force at one end, the effort force in the middle, and the pivot at the other end.

And as you can see here, I use a large effort force to produce a smaller load force.

And an example of that is tweezers.

And again, we'll have a look in a bit more depth at tweezers in a moment.

So we said at the beginning of this learning cycle that some levers are easy to spot, but other levers are more difficult.

We'll start by looking at some of the easiest levers to spot.

This is a typical crowbar lever, or pry bar, and it's very easy to spot.

It's just a simple metal bar with a curved parts towards one end, where the pivot point is.

And you can use it to lift up very heavy objects by applying a downwards effort force.

An effort force on one end of the crowbar will produce a load force on the other end.

And depending on where you push on the lever, you can get a large load force, so you can lift very large objects with a smaller effort force.

So the pivot of that crowbar is in between the effort and the load there.

So that was an obvious lever, but this second one is much less obvious, but it works in the same way.

I've got a ring pull on a can here.

And that operates as a simple lever.

There's a pivot point in the centre there.

And if I pull on this end, the large round end of the ring pull, and pull upwards on it, what will happen is that lever will rotate around the pivot point.

And that will cause the other end of the ring pull to be pushed downwards and produce a load force that acts downwards.

And that load force acting downwards will produce quite a large force on the ring of the can.

And that'll push inwards.

And you'll be able to open it.

So the ring pull is an example of an unobvious lever that works basically in the same way as a crowbar.

We've got a pair of connected levers here in a pair of scissors.

So scissors are just two levers connected together with a sort of pin in the centre.

I put an effort force by squeezing inwards on the two handles.

So I'm operating two levers at the same time here.

And they rotate around that pivot, where the pin is there.

And what that will do is cause a large effort force on the blades of the scissors.

And that effort force will be large enough to cut through materials.

So two connected levers acting as a pair of scissors.

But again, it's a simple system of effort on one side, load on the other, and pivot in the centre, so two levers.

Okay, let's see if you can identify effort, load, and pivot.

So I've got another lever here.

A screwdriver is being used to take the lid off a tin of paint.

And I've labelled three things on it, A, B, and C.

And I'd like you to match them to effort, load, and pivot by drawing some lines.

So pause the video, draw the lines connecting the labels and the names, and then restart when you're ready.

(audio mutes) Okay, welcome back.

And hopefully, you connected these correctly.

Let's have a look.

We should have connected A to the load.

So A is where I'm putting a large force on the lid of the tin of paint, and hopefully opening it.

So that's where the load is.

B is the pivot point.

So I'm pushing downwards on the screwdriver.

And it's rotating around the edge of the can of paint.

So that's where it's pivoting, so a pivot point.

And C then, must be where we're putting the effort.

And putting the effort downwards onto the screwdriver and that's causing the rotation.

So as I push downwards, it rotates and pops the lid of the paint can off.

Well done if you got that.

So let's have a look at another type of lever.

And I've got a wheelbarrow here.

And it doesn't look like a lever at first glance.

But I can identify the load, effort, and pivot, and show that it is a lever.

So first of all, I've got the pivot, the pivot point's on the wheel of the wheelbarrow.

And that's the point where it'll rotate when I try to lift it up.

So there's the pivot.

Then I've got the weight.

And the weight of the soil and moving here, that's gonna act as the load on this lever.

So I've got quite a large amount of soil in there.

I've got quite a large load.

And third of all, when I touch the handles and try and lift them up, I put the effort force on those handles.

So as you can see, I've got the structure of a lever there.

I've got an effort force in one direction, I've got the weight force in the opposite direction.

And I've got a pivot point.

So the wheelbarrow is not an obvious lever, but it is acting as a lever.

And it allows me to use a smallish effort force to lift quite a lot of soil.

So it's a very useful device.

I've got yet another example of a lever here.

And this one's a bit unusual because it's not used to produce large forces.

It's actually used to produce smaller forces.

So I've got the three parts, again.

I've got the load force.

And in this case, the load force is gonna act on the end of the tweezers, the bit where I pluck some hairs out width.

The second bit is the middle part of the lever, and that's where I squeeze.

And that's where I'm putting the effort force in this lever.

So I'm putting the effort force in the middle, the load force at one end.

And the pivot point is where the two parts of the lever are joined.

It's at the other end of the lever.

So this is a fairly unusual structure for a lever, but it's got the three component parts, a pivot point, an effort point, and a load point.

So it is a lever.

So tweezers aren't obvious, but they're definitely levers.

So far, all the examples of levers we've seen are just simple straight lines really with a load, effort, and pivot.

But there are some levers that are even more difficult to spot.

And one of them's a steering wheel.

So on a steering wheel, I can put an effort force on one part of it.

I put the effort force on the outer part of the wheel.

So I'll turning it here anti-clockwise by putting an effort force.

I might also be pushing up on the other side of the lever.

So we might have two effort forces at the same time here.

And the wheel's gonna rotate around its central point.

So it's pivoting around an axle there in the middle.

And finally, the load acts at the same point.

It acts at that axle point towards the centre.

So I have got the three things necessary for lever, again.

I've got a point where it rotates, the pivot.

I've got a point where the load is.

And I've got a point where the effort is.

So I've got a lever here that will allow me to turn things.

Okay, let's see if you can spot the features of a lever with this question.

The image shows a wheel being used to steer a large boat.

Which two statements are correct? Is it the arrows? And you can see the red arrows there.

The arrows show the load forces, B, the arrows show the effort forces, the pivot is at point Y, or the pivot is at point X.

So which two of those are correct? I'd like you to pause the video, select the two correct answers, and then restart, please.

(audio mutes) Okay, welcome back.

Well, you should have chosen these two.

The arrows are showing where the effort force is.

So that's where I'm holding onto the wheel and trying to turn it.

That's where I'm putting my effort in.

And the pivot is at the centre.

It's rotating around the centre when you turn the wheel, so that's the pivot point.

Well done if you've got those two.

Okay, it's time to check if you can spot the key features of lever.

So I've got a question to help you with that here.

So in task B, what I'd like you to do is to state which of those four pictures shows a lever.

Then for each of them, I'd like you to point out where the pivot point is by drawing a line and labelling it, please.

And finally, I'd like you to draw arrows to show where the effort forces would need to be applied to each of the levers.

So I'd like you to pause the video, answer those three questions, and then restart once you've done them, please.

(audio mutes) Okay, welcome back.

Let's see which of those were levers.

Well, actually it was all of them.

All four of those pictures show examples of levers, or at least you can see some levers in the pictures.

In the first picture, the pivot is the centre part.

You're gonna rotate the tap.

And I've drawn a red arrow to show the direction that I'd rotate this tap to turn the hot water on.

So I've got a pivot point and an effort point there.

And the second one, I've got a pivot there in the middle.

And I've got the effort by sitting on that end of the seesaw, so that's an example.

And the third one, I've got a steering wheel.

And that rotates around the centre.

So the pivot point's in the centre and the effort's around the outside.

So I've drawn two force arrows there to show the direction of the arrows.

Sorry, the direction that I rotate the wheel.

And in the third one, again, I've got a pivot point in the middle there, on that point where I can turn the can opener.

And I've drawn the two forces that I would put onto the can opener to make it turn, so the two effort forces.

But actually, there's a extra lever hidden away there.

Some of you might have noticed the door handle.

Or sorry, the door window control.

I could wind that down to open and close the windows of the car, if it still had windows that functioned.

So there's an extra lever you might have spotted.

Well done if you've got all those.

Okay, now we're onto the third and final part of the lesson.

And in this, we're gonna start considering the sizes of those forces that are acting on levers.

So we'll look at the relationship between the effort force you put in and the load force you get out, and see what levers do to those two.

So I'm gonna start by saying the effort and the load force on the lever are not equal and opposite forces.

Most levers are specifically designed to make those forces different sizes.

That's the whole point of most levers.

So I've got a lever here.

And I've got an effort force on it and a load force on it.

And the lever's a simple solid bar operating around a pivot.

And as you can see from my diagram, I've got a small effort force.

And it's producing a large load load force.

Most levers are designed to do exactly that.

You put a small effort in pushing with a force, of say, 10 newtons, and that will produce an output force that might be 100 Newtons, or 150 Newtons, much larger than the force that you can put in.

Those type of levers are the most common.

And they're called force multipliers because they're multiplying the effort you put in to produce a larger load force.

A crowbar is a good example of a force multiplier.

And a force multiplier is something that increases the force you put in.

So you put in a small effort.

And it increases that and produces a much larger load force.

So you can see, this crowbar is being pushed down at one end a long way away from the pivot.

And it's producing a very large load force upwards, which is much, much closer to the pivot.

So you should be able to see that there's some sort of relationship between the distance from the force to the pivot, and the size of that force.

So the long lever can be used to lift very, very heavy objects with fairly small effort forces downwards.

The size of the load force that you actually produce from a lever depends on two main factors.

So let's look at the first of those.

And that's the size of the effort force.

And as you'd expect, if I put an effort on one end of this lever and it's gonna rotate around that pivot there, it's gonna produce an upward load force on the other end of that lever.

If I then push down harder, increasing the effort force, as you'd expect, the load force is going to increase as well.

So increasing the effort increases the load force.

They both go up.

And if they increase the effort further, pushing down harder, the load force increases as well.

So there's a simple relationship between those two.

If you push harder, do more effort, then you can lift a larger load.

And if you reduce your effort, you're gonna lift a smaller load.

The second factor is a little bit more complicated.

It's to do with the distances between the forces.

And not each other, the distances between them and the pivot point on the lever.

So I've got an uneven lever here.

And the load force is going to increase when the load is further from the pivot than the effort force.

And the load force is gonna decrease if it's closer to the pivot than the effort force.

So I'll show you examples of that.

I'll put an effort force here and a load force.

And they're about the same distance from the pivot.

And they're equal in size.

So when those two forces are equal distance from the pivot, they're equal in size.

I push down with 10 newtons, I get an upward force of 10 newtons as well.

But if I put my effort force closer to the pivot and I push down with those 10 Newtons, the load force I get out is much less.

So I've actually decreased.

I'm putting more effort in than I'm getting load force.

And that's because I'm pushing much closer to the pivot than the load is.

And the third scenario is if I push further away from the pivot.

So I'm putting my effort force much further from the pivot, like I did with the crowbar.

And what I get out this time is a much greater load force.

I can double the load force easily if I'm twice as far away from the pivot.

So the relationship between the two forces depends on how far away each of them is from the pivot point.

Okay, let's check if you understood those ideas.

Which of these arrangements is gonna produce the largest load force on the ball? So look carefully at a three diagrams, A, B, and C.

And as you can see, I've got different effort forces on there.

And I've got a ball positioned at exactly the same position in each case.

And I want you to decide, which one of those arrangements is gonna produce the largest upward load force on that ball? So pause the video, make your selection and restart, please.

(audio mutes) Okay, welcome back.

And hopefully, you chose B.

And the reason B is the correct answer is because I've got the large effort force there.

And it's also far from the pivot.

So in scenario A, I've got the same distance to pivot, but I'm pushing down with a smaller force.

And in scenario C, I've got the same effort force, but it's closer to the pivot.

So scenario B is the one that's gonna produce the largest upward force 'cause it's furthest from the pivot and the largest force.

Well done if you've got that.

Now, bearing in mind what we just said about load forces and the relationship to the distance of the pivot, you should be able to see that the force produced by a pair of scissors is actually going to vary along the blades because each part of those blades is gonna be a different distance from the pivot.

So when I put a force on these scissors here and I look close to the pivot point, what that's gonna do is produce a very large force close to the pivot.

If I put the same force and look at the force produced near the tips of the scissors, that's gonna be a much smaller force.

And you probably experience that when you're trying to cut through something, like thick card.

The end point of the scissors doesn't really cut through very easily.

Whereas if you put it the card close to the central pivot point, you get a much easier cut.

So that force, that load force, is varying along the length of the blades.

So let's see if you can apply that lineage to a slightly different scenario.

I've got some bicycle brakes here.

And I'd like to know, how can the turning effect on those brakes and that lever be increased? Can it be increased by pulling it further from the pivot, pulling it closer to the pivot, using a larger effort force on it, or using a smaller effort force? And I'd like you to choose the two correct answers, please.

So pause the video, choose your answers, and restart.

(audio mutes) Okay, welcome back.

And the two answers you should have chosen are pulling it further from the pivot and using a larger effort force.

If you pull further from the pivot, you're gonna produce a larger load force.

And that's why these brake levers are so long.

So you can grip near the end and produce a very large force.

Also using a larger effort force, pulling hard on the brakes will cause it to produce a larger load force as well.

So well done if you selected those two.

Okay, it's time for the final task with lesson task C.

And I'd like you to apply your knowledge of levers to try and solve this.

Hannah's trying to cut a thick metal wire with some wire cutters, as you can see in the diagram there.

And she's squeezing the wire cutters in the middle of the handles.

So you can see that marked with those two red arrows.

I'd like you to label the load, effort, and pivot on that diagram of the wire cutters, please.

And then, I'd like you to describe how she could increase the turning effect of the cutters, so she can get a larger force on the wire and cut through it successfully.

So what I'd like you to do is to answer those questions, pause the video, answer, and then restart.

(audio mutes) Okay, welcome back.

Hopefully, your diagram looks a little bit like this one.

So I've labelled this.

The effort force is the force she's putting on those handles.

So she's squeezing those inwards.

So those are the two effort forces.

The load forces will be on the wire itself, so where the blades of the wire cutters are actually squeezing on the wire to cut through it.

And the pivot is the point where those two parts of the wire cutters are joined together, and a little screw there where they'll rotate around.

So that's the pivot point.

The answer to question two, your ideas could include something like this.

If she squeezes with a greater force, the harder she squashes those two handles, the greater the load force will be.

We saw that earlier in the lesson.

And the second thing she could do is she could push further from the pivot.

So if she holds those handles a bit further, instead of squeezing near the centre, squeezing near the ends, then she'll generate a much larger load force.

And she'll be able to cut through the wire more easily.

And she could also make sure that the wire in between the two blades is very close to the pivot.

And that will generate a much larger force, as you saw with the scissors earlier.

You'll get larger load forces close to the pivot, so you'll cut through things more easily.

Well done if you've got those.

Okay, we've reached the end of the lesson.

And here's a summary of what you should have learned as we went through it.

So levers are simple machines.

And they use a turning effect of forces.

And a lever always has these three features, a pivot, an effort force, and a load force acting on it.

Most levers are designed to be force multipliers.

They generate a larger load force than the effort force you put in.

But there are some exceptions.

And you may see those in future lessons.

And there are three different types of levers that all depend on the relationship between where the effort is, where the pivot is, or what the load force is.

The most common lever is that first one, the top diagram.

But there are other designs as well, as you can see from the other two, where the effort, load, and pivot are in different position.

Well done on reaching the end of this lesson.

Hopefully, I'll see you in the next one.

Goodbye.