# The Science of Simple Machines

In this worksheet, students will be challenged to look at how simple machines operate, how they change the effect of forces and to attempt some basic calculations on their operation.

Key stage:  KS 2

Curriculum topic:   Forces

Curriculum subtopic:   Mechanisms: Levers, Pulleys and Gears

Difficulty level:

### QUESTION 1 of 10

So, you've learned that simple machines are there to make a job easier to carry out. For example, you've found out that a lever works on the principle that the further from the fulcrum a force is applied, the greater the effect (or turning force) it has. That means that a door handle is almost always placed at the edge of a door, furthest from the hinges so that you use the minimum effort to open the door.

Then again, a pulley is a machine that allows you to change the direction of a force.

Imagine you are sailing your dinghy and want to raise the sail - imagine having to sit at the top of the mast, pulling it up! Fortunately, attaching the sail to a pulley enables you to keep your feet on the deck and pull down (with gravity) to raise the sail.

Gears are terrific as not only can they change the amount of force used, but they can also change the speed.

You'll know this from your bike, in order to go faster you change gear and move the chain on to one of the smaller cogs on the back wheel.

In this activity we're going to look a little bit more deeply at what is actually going on with the machines and...whisper this...it sometimes involves some Maths!

Here is a picture of two gear wheels meshed together by their teeth.

Let's say that the larger gear wheel has 40 teeth and the smaller one has 20 teeth.

If the larger gear wheel makes one complete rotation, how many rotations do you think the smaller one will have to make?

0.5

1

1.5

2

This time, imagine that the larger gear wheel has 30 teeth to the smaller wheel's 20 teeth.

Now, how many rotations will the smaller wheel have to make if the larger gear wheel goes round once?

0.5

1

1.5

2

Whereas gears change the speed at which things turn, pulleys change the direction of the pulling force. Look at this picture of a simple pulley system.

The person is pulling down to lift the weight up. The advantage of this arrangement is that you're working with gravity to pull the load up against it.

So, if the mass being lifted is 20kg, what force do you think the person will need to use on the rope to lift the mass up (remember that 1kg weighs 10N).

Write your answer in the two boxes: number first and then unit (label).

0.5

1

1.5

2

Not only do pulleys change the direction of the force (you pulling down to lift the load up) but by joining them together they can share out the load, meaning that you use less effort to do the work of lifting.

Here is an arrangement of two pulleys joined together:

Say you had a load of 60kg to lift with this arrangement. Predict what force you think you'd need to pull with.

300N

60kg

600N

1200N

You'll find levers in so many of the things you often use.

Below is a list of objects, tick the ones that use a lever to make them work.

Drinks can ring pull

Soap dispenser

Door handle

Spanner

Bookcase

Jam jar lid

Stapler

Smartphone charger

Pencil sharpener

Levers work as force multipliers, meaning that the further a force is from the fulcrum, the more effect it has.

Try this see-saw puzzle.

Turning force on the left is:   3N x 2cm = 6Ncm (3 x 2 = 6)

Turning force on the right is: 1N x 6cm = 6Ncm (1 x 6 = 6)

As you can see, the force on the right is only 1N but because it's further from the fulcrum/pivot it has a greater effect and can balance the 3N weight.

Did you see how we worked that out? By multiplying each side! As long as both sides work out to the same answer, the see-saw balances.

Try this one yourself.

How far from the fulcrum would the 2N have to be placed to make the see-saw balance?

2cm

3cm

6cm

7cm

Let's try another on.

What force (or weight) is needed 6cm from the fulcrum to balance the 4N weight placed 3cm on the left?

1N

2N

4N

5N

Here is a family sitting together on a see-saw with their feet on the ground.

If the turning force of Dad and son on the left is 800Nm and the turning force of Mum and daughter is 600Nm, who will need to move closer to the fulcrum to make it balance?

Tick two answers you think might be correct.

Son

Mum

Daughter

Here is a big military aircraft being loaded with crates.

The person in charge of the loading has to make sure that the load is balanced, otherwise the plane won't be able to take off.

If we imagine the plane and the crates like a see-saw, it might look like the image below.

The fulcrum is about in the middle of the plane.

If the plane is already loaded with 40 000N weight of crates, and there's another 30 000N of crates to go at the back of the plane, where should they go?

At exactly 10m on the right

Less than 10m on the right (closer to the fulcrum)

More than 10m on the right (further from the fulcrum)

Here is a man using a long metal lever to try to move a large block of stone.

Let's imagine that the block of stone weighs 1000N and it's at 20cm from the fulcrum of the metal bar.

The man is pushing down 200cm from the fulcrum.

What force must he use to move the block?

10N

100N

200N

1000N

• Question 1

Here is a picture of two gear wheels meshed together by their teeth.

Let's say that the larger gear wheel has 40 teeth and the smaller one has 20 teeth.

If the larger gear wheel makes one complete rotation, how many rotations do you think the smaller one will have to make?

2
EDDIE SAYS
Was that ok? 40 teeth go round once and the 20 teeth of the smaller gear wheel will have to go round twice to match it. Make sense? In simple maths, it's 40 ÷ 20 = 2. Great work! Let's continue.
• Question 2

This time, imagine that the larger gear wheel has 30 teeth to the smaller wheel's 20 teeth.

Now, how many rotations will the smaller wheel have to make if the larger gear wheel goes round once?

1.5
EDDIE SAYS
So, the larger gear wheel has 30 teeth and goes around once. When 20 of those teeth have gone past the 20 teeth of the smaller wheel, the smaller one's gone around once. But there are still 10 teeth left. So, the smaller wheel has to go halfway round again by the time the larger wheel has completed one revolution. So, the smaller wheel goes around 1.5 times. In simple maths it's 30 ÷ 20 = 1.5.
• Question 3

Whereas gears change the speed at which things turn, pulleys change the direction of the pulling force. Look at this picture of a simple pulley system.

The person is pulling down to lift the weight up. The advantage of this arrangement is that you're working with gravity to pull the load up against it.

So, if the mass being lifted is 20kg, what force do you think the person will need to use on the rope to lift the mass up (remember that 1kg weighs 10N).

Write your answer in the two boxes: number first and then unit (label).

EDDIE SAYS
First off, you need to realise that the pulley is only changing the direction of the force, you still need to pull with the same force as the load - it's just pulling downwards, which is way easier than lifting it up in your arms. So, if 1kg weighs 10N, then 20kg must weigh 200N (that's 20 x 10 = 200). If you put 'Newtons' as the label, you're right, but we always abbreviate the units. Imagine having to write out 'millimetres' every time!
• Question 4

Not only do pulleys change the direction of the force (you pulling down to lift the load up) but by joining them together they can share out the load, meaning that you use less effort to do the work of lifting.

Here is an arrangement of two pulleys joined together:

Say you had a load of 60kg to lift with this arrangement. Predict what force you think you'd need to pull with.

300N
EDDIE SAYS
The clever thing with joining two pulleys together is that they share (by half) the load you're lifting, so you only need to use half the force. Lifting 60kg? That's a 600N load, so you only need to use half of that = 300N. Brilliant!
• Question 5

You'll find levers in so many of the things you often use.

Below is a list of objects, tick the ones that use a lever to make them work.

Drinks can ring pull
Door handle
Spanner
Stapler
EDDIE SAYS
The problem with this is that there are so many different types of everything! Take a door handle, most of them are horizontal and you push down on the lever - but round ones don't work like that. Sorry if that's what you chose! A wooden bookcase, for example, is not based on leverage, but there are some that seem to magically stick to the wall and do use leverage - but they're not that common. Every time you open a can of fizzy drink, you're using a lever. If you're digging with a spade or stapling some work together, levers are involved. They are immensely useful!
• Question 6

Levers work as force multipliers, meaning that the further a force is from the fulcrum, the more effect it has.

Try this see-saw puzzle.

Turning force on the left is:   3N x 2cm = 6Ncm (3 x 2 = 6)

Turning force on the right is: 1N x 6cm = 6Ncm (1 x 6 = 6)

As you can see, the force on the right is only 1N but because it's further from the fulcrum/pivot it has a greater effect and can balance the 3N weight.

Did you see how we worked that out? By multiplying each side! As long as both sides work out to the same answer, the see-saw balances.

Try this one yourself.

How far from the fulcrum would the 2N have to be placed to make the see-saw balance?

3cm
EDDIE SAYS
How did you find that? Ok? To be honest, to start off with its just simple multiplication. Left-hand side is: 3 x 2 = 6. That means that, if it's going to balance, the right-hand side must equal 6 as well. So, the 2N weight must be 3cm out for the turning force to be 6. Got it? Don't worry if not let's attempt some more examples.
• Question 7

Let's try another on.

What force (or weight) is needed 6cm from the fulcrum to balance the 4N weight placed 3cm on the left?

2N
EDDIE SAYS
Are you getting the hang of this? On the left it's 4N at 3cm out, so 4 x 3 = 12. Remember, the other side of the see-saw must be 12 too if it's going to balance. So, 6 times what equals 12? 2, of course! That means that the load must be 2N if it's going to be placed 6cm from the fulcrum. Briefly: 4 x 3 = 12 on the left; 6 x 2 = 12 on the right.
• Question 8

Here is a family sitting together on a see-saw with their feet on the ground.

If the turning force of Dad and son on the left is 800Nm and the turning force of Mum and daughter is 600Nm, who will need to move closer to the fulcrum to make it balance?

Tick two answers you think might be correct.

Son
EDDIE SAYS
The combined turning force of dad and son = 800Nm compared with Mum and daughter at 600Nm. So, the lads are the heavier. This then means that at least one of them has to wriggle towards the fulcrum of the see-saw to make it balance, otherwise it's always going to tip down their end and ruin the fun!
• Question 9

Here is a big military aircraft being loaded with crates.

The person in charge of the loading has to make sure that the load is balanced, otherwise the plane won't be able to take off.

If we imagine the plane and the crates like a see-saw, it might look like the image below.

The fulcrum is about in the middle of the plane.

If the plane is already loaded with 40 000N weight of crates, and there's another 30 000N of crates to go at the back of the plane, where should they go?

More than 10m on the right (further from the fulcrum)
EDDIE SAYS
To be honest, you don't need to actually work this one out. The heavier load is at 10m inside the plane, so your knowledge of levers tells you that the lighter load will need to be placed further away from the fulcrum on the other side to balance it out. You're nearing the end of the activity, one more question left!
• Question 10

Here is a man using a long metal lever to try to move a large block of stone.

Let's imagine that the block of stone weighs 1000N and it's at 20cm from the fulcrum of the metal bar.

The man is pushing down 200cm from the fulcrum.

What force must he use to move the block?

100N
EDDIE SAYS
Ok, so hardest one at the end (you can always sketch a lever diagram out for yourself to help you). We have 1000N x 20cm = 20 000Ncm. On the other side, it's 200cm. How much force must he push with to balance the 20 000Ncm total? That's 20 000 ÷ 200 = 100N. In other words, what times 200 equals 20 000? That'll be 100!
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