Simple Machines

Simple machines are basic tools that make work easier by changing the amount or direction of a force. A force is a push or a pull. Simple machines do not have motors or moving parts that run on fuel. They are some of the oldest tools humans ever made. People have used them for thousands of years to lift heavy things, split hard things, and move loads across long distances.

Scientists usually list six simple machines. They are the lever, the pulley, the wheel and axle, the inclined plane, the wedge, and the screw. Every complicated machine you see, from a bicycle to a car engine, is built out of these six parts working together.

A lever is a stiff bar that turns on a point called a fulcrum. A seesaw is a lever. So is a crowbar and the claw end of a hammer. When you push down on one side, the other side lifts up. A pulley is a wheel with a rope or chain running over it. Pulleys let you pull down on a rope to lift something up, which is much easier than lifting it straight. Flagpoles, window blinds, and cranes all use pulleys.

A wheel and axle is a round wheel attached to a rod through its center. Doorknobs, steering wheels, and car tires all work this way. An inclined plane is a ramp. Instead of lifting a heavy box straight up, you can push it up a ramp, which takes less force but over a longer distance. A wedge is two inclined planes stuck back to back, like the blade of an axe or the point of a nail. Wedges split things apart. A screw is an inclined plane wrapped around a pole. Screws hold wood together and lift water from wells.

Simple machines do not give you energy for free. They trade force for distance. To lift a heavy rock with a lever, you push down a long way on the other end. The rock only rises a little. You use less force, but across more distance. The total work stays the same.

Ancient people used simple machines to do amazing things. Egyptian workers probably used ramps and levers to move the huge stones of the pyramids. Roman soldiers used pulleys to lift water and build walls. Every time you ride a bike, open a door, or cut paper with scissors, you are using simple machines that have not changed much in thousands of years.