What are simple machines?

A machine does not need an engine. A simple machine just helps you push or pull more easily. It can make a force bigger, change its direction, or let you apply it more conveniently. There are six types.

1. Lever. A rigid bar that turns on a fixed point, the fulcrum. You push on one end (the effort) to move a load at the other. Examples: a seesaw, a crowbar, a wheelbarrow, scissors (two levers joined).
2. Wheel and axle. A wheel fixed to a rod. Turning the large wheel turns the rod with more force, as with a screwdriver handle, doorknob or steering wheel.
3. Pulley. A wheel with a rope round it. It changes the direction of a pull, such as raising a flag, and several pulleys together make heavy lifting easier.
4. Inclined plane (ramp). A slope. It is easier to push a heavy box up a ramp than to lift it straight up.
5. Wedge. A double ramp that splits things apart: a knife, an axe, a doorstop.
6. Screw. A ramp wound round a rod. It turns small twisting efforts into a strong pull, as in a jar lid or a bolt.

There is a catch. Simple machines do not give you free energy. If a ramp lets you use less force, you have to push over a longer distance. If a lever lets you lift a heavy rock with a small push, your end moves much further than the rock does. You trade force against distance, and the total work stays the same (apart from some lost to friction).

Many everyday objects combine them. A bicycle uses wheels and axles, levers in the brakes and pedals, and gears. A pair of scissors combines levers and wedges. These machines work using forces, and the pull of gravity is often the load.