How do levers help us lift heavy objects?

1. The puppy's ball has rolled under a big rock. Maya tries to lift the rock with her hands, but it is far too heavy. She needs a machine to help her.
2. Maya slides one end of a strong plank under the rock. Then she pushes a block under the plank, close to the rock. The plank is now a lever, and the block is its pivot.
3. Maya pushes down on the long end. The plank tips on the block, and the short end lifts the rock. Her small push has turned into a big lift!
4. Why does it work? Maya's side of the plank is long, and the rock's side is short. The longer your side is compared with the load's side, the less you have to push.
5. There is a catch. Maya's end moves down a long way, but the rock rises only a little. A lever lets you push gently, but you have to push farther.
6. A seesaw is a lever with its pivot in the middle. A small child sitting far out can balance a bigger child who sits close in. Scissors, wheelbarrows and bottle openers are levers too.

Every lever has the same few parts. Tap each one to see what it does.

• Beam. The bar of the lever. It must be stiff and strong, because a bar that bends or snaps cannot lift anything.
• Pivot. The point the beam turns on, also called the fulcrum. Moving it changes everything: put it close to the load and lifting gets easy.
• Load. The thing being lifted or moved. Gravity pulls it down with a force called its weight.
• Effort. The push or pull you put in. With a good lever, the effort can be much smaller than the load.
• Load arm. The part of the beam between the pivot and the load. Making it shorter makes the lift easier.
• Effort arm. The part of the beam between the pivot and your push. The longer it is, the less you have to push.

Drag the pivot along the plank and try different loads. Watch how big a push is needed, and how high the load goes.

Experiment: Where should the pivot be so that a small push lifts the heavy rock?

1. Choose the rock. Drag the pivot to the middle of the plank. Can Maya lift it?
2. Drag the pivot close to Maya, then close to the rock.
3. Now try the pumpkin and the crate. Where can the pivot be for each one?

What we found: The closer the pivot is to the rock, the smaller the push you need, because your side of the plank gets longer and the rock's side gets shorter. But the rock does not rise as high. A lighter load can be lifted with the pivot almost anywhere.

Turn on JavaScript to try it yourself.

Lift the 100 kg rock at least 33 cm so the puppy can get its ball. For 3 stars, do it with just one child pushing.

A lever is one of the simplest machines there is: a stiff bar and something for it to tip on. The point it tips on is called the pivot. The thing you want to move is the load, and your push or pull is the effort.

The secret is distance from the pivot. Think of a seesaw. If you sit far out at the end, you push down with a lot of turning power. If you sit close to the middle, you have much less. So when the load is close to the pivot and you are far away from it, your small push can beat a big weight. If your side is four times longer than the load's side, you only need to push a quarter as hard.

But a lever does not give you something for nothing. Your end has to move a long way, and the load moves only a little. You push gently for a long distance, and the load is pushed hard for a short distance.

Levers are hiding everywhere. Scissors, pliers and crowbars have the pivot in the middle. A wheelbarrow has its pivot at the wheel and the load in the middle, so you lift only part of the weight. Tweezers and brooms work the other way around: you push in the middle and the tip moves farther and faster. Even your arm is a lever, with your elbow as the pivot. Our seesaw comparison stops working here, because these levers do not all have the pivot in the middle.

Key words

Lever

A stiff bar that turns on a pivot to move a load.

Pivot (fulcrum)

The point a lever turns on.

Load

The thing a machine lifts or moves, or the force needed to move it.

Effort

The push or pull you put into a machine.

Mechanical advantage

How many times a machine multiplies your push.

Moment

The turning power of a push: bigger when the push is farther from the pivot.

Check your thinking

1. To lift a heavy rock with a small push, where should the pivot be?

   Show the answer

   Close to the rock. A pivot near the load makes your side long and the load's side short, so a small push is enough.

2. A small child wants to balance a bigger child on a seesaw. What should they do?

   Show the answer

   The small child sits far from the middle and the big child sits close to it. A smaller weight farther from the pivot can balance a bigger weight closer to it.

3. A lever lets you lift a rock with a small push. What do you give up?

   Show the answer

   Your end has to move much farther than the rock rises. A lever trades distance for force: a gentle push over a long way becomes a strong push over a short way.

4. A 600 N load sits 0.5 m from the pivot. What effort, 2.0 m from the pivot on the other side, balances it?

   Show the answer

   150 N. 600 N × 0.5 m = 300 newton meters, and 300 ÷ 2.0 m = 150 N.

5. Which of these is a lever?

   Show the answer

   A pair of scissors. Each blade of a pair of scissors is a bar that turns on the pivot in the middle.

6. What is the point a lever turns on called?

   Show the answer

   The pivot, or fulcrum. The pivot is the fixed point the bar tips on. Fulcrum is another word for it.