D. Structures and Mechanisms · Simple Machines and Movement

Pulleys: Pull Down to Lift Up

D2.3 D2.4 D2.5 A1.2 A1.3About 35 minutes

Learning goals

I can describe a pulley: a wheel with a rope that runs over it.
I can explain that a pulley can change the direction of a force: pull down to lift up.
I can find pulleys in daily life, like a flagpole, window blinds and a crane.
I can build a simple pulley and compare lifting with it and without it.

Words to know

pulley
A wheel with a groove around it that a rope or string runs over.

direction
The way something moves or the way a force pushes or pulls: up, down, left, right.

fixed pulley
A pulley that stays in one place, like the one at the top of a flagpole.

movable pulley
A pulley that is attached to the load and moves up with it.

The flag mystery

On Canada Day, someone raises the Canadian flag up a tall flagpole. They do not climb the pole! They stand on the ground and pull down on a rope. And the flag goes up.

How does pulling down make something go up? At the top of the flagpole is a small wheel called a pulley.

What is a pulley?

A pulley is a wheel with a groove around its edge. A rope sits in the groove and goes over the wheel.

When you pull one end of the rope down, the rope slides over the wheel, and the other end goes up. The wheel turns as the rope moves.

So a pulley changes the direction of your force. Pulling down is often easier than lifting up, because you can use your body's weight to help you pull.

An old metal pulley wheel hanging from a beam on a red barn, with a rope going over it and tied around a bale of hay. — The rope sits in the groove of the pulley wheel. Pulling one end of the rope down lifts the hay bale up. AI-generated image

A fixed pulley. Pull the rope down, and the load goes up.

Two kinds of pulleys

A fixed pulley stays in one place, like the one at the top of a flagpole. It changes the direction of your pull. You pull down; the load goes up. The pull you need is about the same as lifting it yourself.
A movable pulley is attached to the load and moves up with it. The rope holds the load up on two sides, so you need less force. But you have to pull more rope.

Big machines like cranes at building sites use many pulleys together to lift very heavy things.

A fixed pulley stays at the top and changes the direction of your pull. A movable pulley rides up with the load, and two parts of the rope share the job, so you need less force.

Pulley	What it does
flagpole	pull down on the rope, the flag goes up
window blinds	pull the cord down, the blinds go up
clothesline between two pulleys	pull the line to move clothes out and bring them back without walking
construction crane	lifts heavy beams high up
elevator	strong cables run over big pulley wheels to lift the elevator car
sailboat	pull ropes on pulleys to raise the sails

Pulleys in daily life

Worked example

Let's figure out the flagpole

Where is the pulley on a flagpole, and how does it help raise the flag?

The pulley is at the top of the pole. It is a fixed pulley.
A rope goes up the pole, over the pulley wheel, and back down. The flag is clipped to the rope.
When you pull down on one side of the rope, the other side, with the flag, goes up.
Without a pulley, someone would have to climb the tall pole to hang the flag. That is hard and not safe!

The pulley at the top changes the direction of the pull. Pull down, and the flag goes up. No climbing needed!

Just for fun

What is a pulley's favourite holiday?

Canada Day, when everyone watches it raise the flag!

Worked example

Let's build and test a pulley

We make a pulley with an empty thread spool on a pencil. A grown-up holds the pencil ends (or tapes them to the edges of two chairs). A string goes over the spool. A small bag of toys hangs on one end.

Ask: Can we make it easier to lift the bag onto a chair?
Build: Slide the spool on the pencil. Tie the bag to the string and put the string over the spool.
Test 1: Lift the bag straight up with a rubber band on the string. The rubber band stretches 5 cm.
Test 2: Pull down on the other end of the string. The bag goes up! The rubber band stretches about 5 cm again (a tiny bit more, because the spool rubs on the pencil).
Think: The pull was about the same, but the direction changed. We pulled down and the bag went up.

A fixed pulley changes the direction of the force. It did not make the pull smaller. To need less force, you would need a movable pulley.

Pulley or wheel and axle?

Both have a wheel! A pulley has a rope that runs over the wheel. A wheel and axle has a rod fixed through the wheel, and no rope is needed.

Hands-on activity

Build a spool pulley

You need: an empty thread spool (or a round toilet-paper tube), a pencil or a chopstick, string (about 1 metre), a small bag or plastic cup with a string handle, a few toys for a load, a rubber band, and a ruler.

Push the pencil through the spool. A grown-up holds the pencil ends up high, or tapes them to the backs of two chairs.
Tie the bag to one end of the string. Lay the string over the spool so the bag hangs down.
Pull down on the free end. Watch the bag go up!
Measure: Loop a rubber band on the end of the string. Lift the bag straight up with the rubber band (no spool). Measure the stretch. Then pull down through the pulley. Measure again.
Improve: Can you raise a toy "flag" up the side of a cardboard tube using your pulley?

What to look for: the pulley lets you pull down to lift up; the stretch is about the same both ways. Safety: keep string away from necks, and don't stand under the hanging load.

Your turn

What is a pulley?

When you pull down on a flagpole rope, which way does the flag go?

What does a fixed pulley change?

Name two places you can find a pulley.

Which kind of pulley moves up with the load?

Why is it easier to pull down than to lift up?

Where is the pulley on a flagpole?

More practice: warm-up

Does a pulley have a wheel?

What goes over the pulley wheel?

You pull the cord on window blinds down. What do the blinds do?

Is a pulley one of the six simple machines?

What lifts heavy beams at a building site?

More practice: on your own

In our spool test, the rubber band stretched about the same with and without the fixed pulley. What did the pulley change?

How is a movable pulley different from a fixed pulley?

Why is a pulley safer than climbing a flagpole?

How is a pulley different from a wheel and axle?

A clothesline runs between a pulley on the house and a pulley on a pole. How does it make hanging laundry easier?

Challenge

A worker must lift a heavy bucket of nails to a roof. Should she use a fixed pulley or a movable pulley if the bucket is too heavy to lift? Explain.

Your spool pulley rubs and squeaks. The pull is a little bigger than lifting with no pulley. Why? How could you improve it?

Design a pulley to lift a basket of toys up to a tree fort. Draw it and explain how it works.

Check your understanding

Quiz

A pulley is a wheel with...

You pull down on a flagpole rope. The flag goes...

What does a fixed pulley do?

Which uses a pulley?

Which kind of pulley lets you lift a load with less force?

Where do builders use pulleys to lift heavy beams?

For parents and teachers

Big idea: A pulley is a grooved wheel with a rope over it. A fixed pulley changes the direction of a force; a movable pulley reduces the force needed (D2.3, D2.4). Measuring the pull with a rubber band compares forces with and without a pulley (D2.5). Building the spool pulley and improving it is engineering design (A1.3), and testing it is a fair test (A1.2).

Science accuracy note: A single fixed pulley does not reduce the force; it changes the direction (with a little extra friction). Your child may expect it to feel easier; that is a great chance to talk about what the measurement shows.

How to help: Look for flagpoles at school, blinds at home, cranes at building sites. Ask, "Which way do you pull, and which way does it go?"

Common difficulties:

Confusing pulleys with wheels and axles. Look for the rope.
Thinking every pulley makes things lighter. Fixed pulley: changes direction. Movable pulley: less force, more rope.
Safety: string near necks, and loads hanging over heads. Supervise closely.