Wheel & axle and Pulley

What is a wheel and axle?

A wheel and axle is a simple machine that is made up of a wheel with a rod called an axle attached in the middle. The wheel and axle rotate together and force is transferred from one to the other. A picture of a wheel and axle can be seen below.

_{This wheel and axle is used to make lifting buckets out of a well easier.}

Other examples of the wheel and axle are screwdrivers, drills, electric fans, doorknobs and the wheels of bicycles and cars. Look at the pictures below. Can you tell which part is the wheel and which part is the axle?

What is a pulley?

A pulley is a simple machine that is made up of a wheel with a groove on its outer edge and an axle. Using a rope, cord or chain, a pulley can be used to make lifting things easier. Look at the diagram showing pulleys below.

Pulleys are used often in everyday life. Pulleys are used in elevators to help them move up and down. Many exercise machines use pulleys to help lift the weights. Cranes use pulleys to help lift heavy loads. Look at the crane in the picture below. Do you see the pully at the top of the crane?