Long ago, people moved huge stones with logs and poles. A pole that turns on a point is a lever, one of the six simple machines.
Key idea
A lever is a stiff bar that turns on a point called the fulcrum. The push you give is the effort; the thing you lift is the load. The farther your push is from the fulcrum, the less push you need.
Why it works
A lever balances when load × its distance = effort × its distance. A far-away push needs less force, but your hand moves farther. You trade distance for force.
Worked example: How much push?
A rock weighing 10 blocks sits 1 step from the fulcrum. You push 5 steps from the fulcrum. How many blocks of push balance it?
- Load × distance: 10 × 1 = 10.
- Effort × 5 must make 10.
- 10 ÷ 5 = 2.
Answer: 2 blocks
Levers are everywhere: a seesaw, a crowbar, a bottle opener, scissors (two levers), a broom and even your arm, with the elbow as the fulcrum.
Common mistake
Thinking a lever gives free energy. You push less, but your end moves a long way while the load moves a little.
Try it at home
- Lay a ruler across a pencil to make a seesaw. Put three coins at one end.
- Press down on the other end with one finger. Then slide the pencil closer to the coins and press again.
- When is it easiest? When the fulcrum is close to the load.
Going further. The Trebuchet Workshop is a giant lever that throws. Archimedes studied levers over 2,000 years ago: see Archimedes: The Works (the young readers' path). Later, Levers in Physical Science.