There are six simple machines. They are the lever, the wheel and axle, the pulley, the inclined plane, the wedge and the screw. Simple machines make work easier. A seesaw is a lever. A compound machine is made of two or more simple machines. Let's look at each of the six, one at a time. First up is the lever.

A lever is a bar that turns around a pivot point called the fulcrum. Here are some levers you may know. Scissors are an example of a lever. A wheelbarrow is a lever, and so is a crowbar. Your forearm is a lever too, with the elbow as its pivot. Try it. Bend your arm and watch the elbow turn.

A ramp is an inclined plane, and so are stairs. Ramps were probably used when the ancient Egyptians built the pyramids, to move large blocks of stone to the top. A ramp makes it easier to move something upward, but the path is longer. A wedge pushes things apart or cuts them. It is made of two inclined planes put back to back. Ask a grown-up to help with sharp or heavy tools.

A doorstop is a wedge, and so is a knife. A wedge can be used to split a log. Now look at the screw. A screw is an inclined plane wrapped around a cylinder. A screw helps to hold things together. It also turns a twisting motion into movement forward or backward.

A pulley is a wheel that a rope goes over. A flagpole uses a pulley to raise the flag. A single pulley changes the direction of a force. Using more than one pulley lets you lift a heavy load with less force. A wheel and axle helps move a load by turning or rolling. A bicycle is an example of a wheel and axle.

Here is the big idea about simple machines. A simple machine can let you use less force, but you must move over a longer distance. Think of a ramp. It is easier to move something upward, but the path is longer. Think of pulleys. Using more than one lets you lift a heavy load with less force. Simple machines make work easier.

Words to know

• lever: turning bar
• fulcrum: the pivot point
• wedge: pushes things apart
• pulley: wheel with rope
• compound: made of parts

The short version

There are six simple machines: the lever, the wheel and axle, the pulley, the inclined plane, the wedge and the screw. Simple machines make work easier. A simple machine can let you use less force, but you must move over a longer distance. A compound machine is made of two or more simple machines.

Quick facts

• A seesaw, scissors, a wheelbarrow and a crowbar are all levers.
• A ramp is an inclined plane, and so are stairs.
• A wedge is made of two inclined planes put back to back.
• A screw is an inclined plane wrapped around a cylinder.
• Using more than one pulley lets you lift a heavy load with less force.