Levers and simple machines
Slide the pivot of a lever and lift a heavy rock with a small push. Weight × distance tells who wins.
Standards: 3-PS2-13-5-ETS1-1
1Wonder
A grown-up and a small child sit on a seesaw. The grown-up is much heavier, yet the child can still lift them. How? And how can one person lift a rock far heavier than they are?
2Explore
This activity needs a bigger screen
Turn your phone sideways, or open this lesson on a tablet or computer. The explanation and quiz below work here.
- Keep the pivot in the middle. How hard do you have to push to lift the 60 kg rock?
- Move the pivot closer to the rock. Now how hard do you need to push?
- Move the pivot close to you. What happens?
- Turn on Show the math. When does the rock go up? Can you make it exactly balanced?
3Explain
The parts of a lever
A lever is a stiff bar that turns on a pivot (also called a fulcrum). The load is what you want to move. The effort is your push.
When both sides are equal, the lever balances. To lift a heavy load with a small push, put the pivot close to the load and push far from it.
4Practice
A heavy friend and a light friend want to balance on a seesaw. Where should the heavy friend sit?
5Recap
- A lever is a bar that turns on a pivot (fulcrum).
- Each side counts weight × distance from the pivot; equal sides balance.
- Pivot close to the load → a small push lifts a big load.
- But your end has to move farther: you trade distance for force.