A simple machine is a basic mechanical device that makes work easier by changing the direction or size of a force. There are six types: the lever, wheel and axle, pulley, inclined plane, wedge, and screw.

Think about using a bottle opener to pop the cap off a glass bottle. Your hand pushes down on one end of the opener, and the other end lifts the cap up with much more force than your hand alone could apply. That's a lever, one of the six simple machines, making your work easier. When you ride a bike, the pedals and gears work as a wheel and axle, turning your leg power into the spinning motion that moves you forward. When you use a ramp to roll a heavy box into a truck instead of lifting it straight up, you're using an inclined plane.

Simple machines don't need electricity or engines. They've been used for thousands of years, from ancient Egyptian workers using levers and ramps to build the pyramids, to modern construction workers using pulleys to lift heavy loads. A doorknob, a knife, a playground seesaw, and even a screw holding a wooden chair together are all examples of simple machines at work. Most complex machines, like cars or cranes, are really just combinations of these six simple machines working together.