What Are Simple Machines?
Six basic devices that make work easier — and they're hiding in almost everything you use every day.
Making Work Easier (Not Less)
In science, work means using a force to move something over a distance. Pushing a heavy box across the floor is work. Lifting a backpack onto a shelf is work. A simple machine is a basic device that makes work easier by changing the direction or amount of force you need to apply. Simple machines don't reduce the total amount of work — they just let you trade force for distance, or change the direction of your push or pull.
Scientists have identified six types of simple machines. Every complex machine — from bicycles to cranes to can openers — is built from combinations of these six.
1. Lever
A lever is a rigid bar that rotates around a fixed point called a fulcrum. When you push down on one end, the other end goes up. Seesaws, crowbars, and scissors are all levers. The farther you sit from the fulcrum on a seesaw, the less effort you need to lift someone on the other side — that's why a small kid sitting far out can balance a bigger kid sitting close to the middle.
2. Wheel and Axle
A wheel and axle is a circular wheel attached to a rod (the axle) that turn together. Doorknobs, steering wheels, and bicycle wheels all use this principle. The wheel gives you a larger surface to apply force to, which means you need less effort to turn the axle. Try opening a door by gripping the tiny axle instead of the knob — it's nearly impossible.
3. Pulley
A pulley is a wheel with a groove that holds a rope or cable. A single pulley changes the direction of force — you pull down on the rope, and the object goes up. Add more pulleys together in a block and tackle system, and you can multiply your force. Construction cranes use multiple pulleys to lift thousands of kilograms with relatively small motors.
4. Inclined Plane
An inclined plane is a flat surface tilted at an angle — a ramp. Instead of lifting a heavy box straight up onto a truck, you can push it up a ramp using less force over a longer distance. Wheelchair ramps, slides, and mountain roads are all inclined planes. The gentler the slope, the less force you need, but the longer the distance you travel.
5. Wedge
A wedge is really two inclined planes stuck together to form a sharp edge. Wedges are used to split things apart or hold things in place. Axes, knives, your front teeth, and even the bow of a ship are all wedges. When you push a wedge forward, it converts that forward force into a sideways force that pushes materials apart.
6. Screw
A screw is an inclined plane wrapped around a cylinder. Look at a screw closely — those spiral threads are just a ramp going around and around. Each turn of the screw moves it forward only a tiny amount, which means you can push something with enormous force using relatively little effort. Jar lids, spiral staircases, and drill bits are all screws.
Compound Machines
Most real-world tools combine multiple simple machines. A pair of scissors uses two levers joined at a fulcrum, with wedge-shaped blades. A bicycle combines wheels and axles, levers (the brake handles and pedals), pulleys (the chain system), and screws (the bolts holding it together). Once you learn to spot simple machines, you'll start seeing them everywhere.
The ancient Egyptians built the pyramids using simple machines that are thousands of years old. They used inclined planes (ramps) to drag massive stone blocks upward, levers to pry blocks into position, and rollers (a form of wheel and axle) to move blocks across the desert — all without electricity or engines.
Last reviewed: April 2026