Machines that multiply your muscles

Imagine you need to haul a bag of shopping across a river on a flying fox, or lift a boat trailer onto a hitch. Your muscles are not strong enough on their own. That is where simple machines come in. They do not create energy. They change how you use it.

The six simple machines

The big trade: force for distance

With one fixed pulley, you pull down to lift a load up. It feels easier because you can use your body weight, but you still pull the full weight. With two pulleys working together (a block and tackle), the load is shared between two strands of rope, so you need about half the force. The catch? You have to pull twice as much rope. Machines always trade force for distance.

Gears and cranks

Gears are wheels with teeth that mesh together. When a small gear drives a big one, the big one turns slower but with more turning force. When a big gear drives a small one, the small one spins faster. Bikes use this: low gears for climbing hills, high gears for speed on the flat. A crank handle is a lever that turns an axle, like the handle on an old well or a fishing reel.

Mechanisms at work in Aotearoa

Gondolas in Queenstown and Rotorua haul cabins up hills with cables, big wheels and motors. Farm gates swing on hinges, and ski lifts loop cables around huge wheels called bull wheels. The EPro8 flying fox challenge asks you to pull a seat back across a river with a crank and a pulley, the same ideas at model size.

Try it yourself

Hang a 1 kg bag of rice from a spring balance. Then lift it using one pulley, then two. Measure the force each time and the length of rope you pull. You will see the trade for yourself.