Simple Machines
Primary 6 · Science and Elementary Technology
Simple Machines
Lesson 1 of 5
14 min
Let's begin
Niyonzima's family harvested their maize, and now a 100 kg sack must go up three steps into the store. Two grown-ups try to lift it and cannot.
So Niyonzima's father lays a long, strong plank from the ground to the store door, loads the sack into a wheelbarrow and pushes it up the plank. Nobody got stronger that afternoon. They used machines.
In science, work is done when a force moves something. Two words help us talk about machines:
A simple machine is a device with few or no moving parts that makes work easier. It does this in one or more of these ways:
Scientists name six simple machines: the lever, the wheel and axle, the pulley, the inclined plane, the wedge and the screw. You will meet each of them in this unit.
No machine gives you something for nothing. When a machine lets you use less effort, you have to move a longer distance. The plank was much longer than the three steps were high, so Niyonzima's father pushed the sack further, but with far less force.
A tool is any object that helps you do a job. Some tools are simple machines, because they change the size or direction of a force. Others are not.
| Simple machines | Tools that are NOT simple machines |
|---|---|
| Bottle opener (lever), axe (wedge), screwdriver (wheel and axle), ramp (inclined plane), flagpole pulley | Ruler (measures), paintbrush (spreads paint), spirit level (checks level), bucket (holds water), broom head (sweeps) |
When two or more simple machines work together, we have a compound machine. A wheelbarrow is a lever with a wheel and axle. Scissors are two levers joined together, with blades that are wedges. A bicycle uses wheels and axles, levers and more.
Lay a pencil on a table. Rest a 30 cm ruler across it, like a seesaw. Put a small pile of coins (the load) near one end and press on the other end (the effort). Now slide the pencil closer to the coins and press again. Which position makes the coins easiest to lift? You have just built your first simple machine.
Tip
Remember the six with a silly sentence: Lazy Wally Pulled In Wet Socks.
Lever, Wheel and axle, Pulley, Inclined plane, Wedge, Screw.
Try each one first, then tap Show answer to check.
In the story, what was the load and what was the effort?
Answer: The load was the 100 kg sack of maize. The effort was the father's push on the wheelbarrow.
Is a bucket a simple machine? Explain.
Answer: No. A bucket only holds water. It does not change the size or direction of a force.
Why is a bicycle called a compound machine?
Answer: Because it is made of several simple machines working together, such as wheels and axles and levers.
In your model lever, where did the pencil have to be to lift the coins most easily?
Answer: Close to the coins (the load), so that your end of the ruler was long.
What you learned today
Sources and credits
This lesson adapts CC BY-SA material and is shared under CC BY-SA 4.0.
Quick check
Match each tool to the simple machine it is.
Tap one on the left, then its partner on the right.
