Science notes, unit 10

Machine

Textbook Science Year 3 (DLP), pages 127–137

What this chapter covers

You can say what a pulley is and name the parts of a fixed pulley (10.1.1)
You can explain how a fixed pulley lifts a load, using a crane model (10.1.2)
You can give examples of how pulleys are used in daily life (10.1.3)
You can name other types of pulleys and say how cranes at a port and a construction site use them (10.1.3)
You can plan and build a working pulley model from recycled materials (10.1.4, 10.1.5)

Lim and his father are on their balcony. Far away, a tall crane is lifting heavy building materials. How can a crane lift such heavy things? It uses a pulley! In this unit you will find out what a pulley is, how it works and where we use it.

Lim looks through binoculars at a crane while his father says the crane lifts building materials with the help of a pulley; a close-up shows the pulley on the crane arm — "The crane lifts the building materials with the help of a pulley."

10.1What is a pulley?

Have you ridden a cable car, like the one at Langkawi or Genting? A cable car also moves with the help of pulleys.

A boy at a cable car station asking how the cable car moves — How does this cable car move? It uses pulleys.

A machine is a thing that helps us do work more easily. A pulley is a simple machine. It helps us lift a load easily using less force.

A load is the heavy thing we want to lift. A force is a push or a pull. With a pulley, we pull the rope and the load goes up.

Parts of a fixed pulley

A fixed pulley is tied to one place. It does not move up or down. It has four parts.

A fixed pulley hung from a ceiling lifts a load when a hand pulls the rope; a close-up labels the groove, wheel, axle and rope — The parts of a fixed pulley.

Part	What it is
Wheel	The round part that turns.
Groove	The deep line around the edge of the wheel. The rope sits in it.
Axle	The rod in the centre. The wheel turns around it.
Rope	It passes through the groove. We pull it to lift the load.

Did you know? The groove stops the rope from slipping off the wheel. It works like the track of a toy train.

Name the part of a pulley that the rope passes through.

Show answerHide answer

The groove.

10.2How a fixed pulley works

Let us look at a crane model. A crane is a tall machine that lifts heavy things. This model has a fixed pulley at the end of its arm.

A crane model with a yellow pulley on the pole and a black pulley at the end of the arm holding a load — The crane model and its parts: base, pole, arm, rope, load and two pulleys.

Parts of the crane model: base, pole, arm, load, one yellow pulley (acts as a motor), rope, one black pulley (acts as a fixed pulley) — The crane model and its parts: base, pole, arm, rope, load and two pulleys.

Crane model photos: Science Year 3 (DLP) textbook, pp. 129–130.

The black pulley is the fixed pulley. The yellow pulley acts like a motor. We turn it to pull the rope. The model only works when all the parts are joined together.

Crane model with the load resting on the base — 1. Before: the load is on the table. 2. While lifting: we turn the yellow pulley and the rope is pulled. 3. After: the load is lifted up high.

A hand turns the yellow pulley; the load is halfway up — 1. Before: the load is on the table. 2. While lifting: we turn the yellow pulley and the rope is pulled. 3. After: the load is lifted up high.

When the rope is pulled, it moves through the groove. The wheel turns. The load is lifted upwards.

Example: pull down, load goes up

Look at a fixed pulley. Your hand pulls the rope down. The load on the other side moves up. Pulling down is easy, because your body weight helps you!

A fixed pulley does not move up and down with the load. Only the wheel turns, on its axle.

Ali pulls the rope of a fixed pulley downwards. Which way does the load move?

Show answerHide answer

Upwards.

10.3Uses of pulleys

Pulleys are all around us. Here are four uses of the fixed pulley.

Raising the flag. We pull the rope down. The Jalur Gemilang goes up.
Lifting water from a well. The bucket comes up easily.
Pulling up fishing nets. Fishermen pull heavy nets full of fish onto the boat.
Lifting building materials. Workers lift buckets of cement to the upper floor.

A pupil raises the Malaysian flag; a close-up shows the pulley at the top of the flagpole — Raising the flag at school assembly (left). Lifting a bucket of water from a well (right).

A man lifts a bucket from a well using a pulley on a wooden frame — Raising the flag at school assembly (left). Lifting a bucket of water from a well (right).

A fishing boat with pulleys on its poles pulling up nets — Pulling up heavy fishing nets (left). Lifting a bucket of cement to the upper floor (right).

A worker on an upper floor lifts a bucket with a pulley; a close-up shows the pulley — Pulling up heavy fishing nets (left). Lifting a bucket of cement to the upper floor (right).

Pictures: Science Year 3 (DLP) textbook, pp. 131–132.

With a pulley or without?

Lifting a bucket from a well with a pulley — With a pulley (left), he pulls the rope down. Without a pulley (right), he must pull the bucket straight up.

Lifting a bucket from a well with only a rope — With a pulley (left), he pulls the rope down. Without a pulley (right), he must pull the bucket straight up.

Which is easier? Using the pulley! Without a pulley, the man must lift the bucket straight up. It is harder and he gets tired fast.

What if the flagpole had no pulley? Someone would have to climb the pole to put the flag at the top. That is hard and not safe!

Other types of pulleys

Besides the fixed pulley, there are other types. Two of them are the compound pulley and the movable pulley.

Left: a compound pulley with one pulley on the ceiling and one on the load. Right: a movable pulley that hangs on the rope and moves with the load — A compound pulley (left) and a movable pulley (right).

Type	What it looks like
Fixed pulley	One wheel tied to one place. It does not move.
Movable pulley	The wheel hangs on the rope and moves up with the load.
Compound pulley	A fixed pulley and a movable pulley used together.

Cranes at the port and at the construction site

A crane at a port lifts a shipping container off a ship — At the port (left), a crane with pulleys unloads containers from the ship to the lorry. At the construction site (right), a crane with pulleys lifts building materials up high.

A tower crane lifts steel beams at a construction site; a close-up shows the pulley hook — At the port (left), a crane with pulleys unloads containers from the ship to the lorry. At the construction site (right), a crane with pulleys lifts building materials up high.

Pictures: Science Year 3 (DLP) textbook, pp. 135–136.

A container is as heavy as many cars. The pulley helps the crane lift it using less force. Without pulleys, building a house or a school would take a longer time and need more workers.

Did you know? Port Klang is one of the busiest ports in the world. Its cranes move thousands of containers every day, all with the help of pulleys.

Give two uses of pulleys in daily life.

Show answerHide answer

Any two: raising the flag, lifting water from a well, pulling up fishing nets, lifting building materials, unloading containers at the port, cable cars.

10.4Make your own pulley model

Here is a real problem. The water supply at an apartment was cut off. People must carry heavy buckets of water from a lorry up the stairs. How can we make it easier?

Residents carry buckets of water up the stairs from a water lorry; a girl asks how to make it easier — The problem: carrying water to the upper floor is hard work.

Scientists and engineers solve problems in steps. You can too!

Step	What we do
1. Find the problem	Carrying water upstairs is tiring.
2. Get an idea	"Let's make a pulley!"
3. Sketch the idea	Draw the pulley on paper first.
4. Prepare materials	Recycled box, plastic bottle, straw, stick, string, glue, scissors, ruler.
5. Build and test	Make the pulley, hang it up and try lifting a small load.

Six photos: A measure and cut the box and bottle; B make a hole in the centre; C attach the parts to the bottle; D insert a straw to make an axle; E pierce the stick through the straw; F hang and test the pulley — Building a pulley model from a box and a bottle.

The two round pieces of the box make the wheel. The cut bottle in the middle makes the groove. The straw is the axle.

A man on an upper floor uses a pulley to lift a bucket of water from the ground — Now water can be lifted to the upper floor easily.

Pictures: Science Year 3 (DLP) textbook, pp. 133–134.

Scissors and cutters are sharp. Ask an adult to help you cut and make holes.

Try it at home: build a crane model from a shoe box and some sticks, like the one below. Can it lift a small packet of tissues?

A crane lorry model made from cardboard with a pulley at the tip of its arm — A crane model made from recycled boxes (textbook p. 136).

Summary

Remember	Key fact
Pulley	A simple machine. It helps us lift a load easily using less force.
Parts of a fixed pulley	Wheel, groove, axle and rope.
How it works	The rope is pulled through the groove. The wheel turns. The load is lifted up.
Uses	Raising the flag, lifting water from a well, pulling up fishing nets, lifting building materials.
Other types	Movable pulley and compound pulley.
Cranes	Port: unload containers from ship to lorry. Construction site: lift building materials.
Pulley model	Problem, idea, sketch, materials, build and test. Use recycled materials.