INSIDE MACHINES
The short lands soon

Force Week 1 · 6 min of play

The Lever

How a kid can lift a grown-up.

2 · The question

A 30 kg kid and an 80 kg grown-up sit on a seesaw. Can the kid win?

3 · Play first

Move the kid. Move the grown-up. Make it balance.

30 kg80 kg
Kid's turning force 294 N·mGrown-up's turning force 785 N·mGrown-up side goes down.

4 · What's happening

  1. 1

    Weight pushes down on the seesaw. That push is a force.

  2. 2

    The further from the pivot you sit, the more the same push turns the beam.

  3. 3

    It balances when both sides turn the beam by the same amount.

5 · The maths

Turning force is called torque. It is force times distance from the pivot.

τ=F×d\tau = F \times dF1×d1=F2×d2(balanced)F_1 \times d_1 = F_2 \times d_2 \quad \text{(balanced)}

30 kg × g × 1.0 m<80 kg × g × 1.0 m

294 N·m<785 N·m

6 · Under the hood

The 3 kinds of lever (for grown-ups)
Class 1

Pivot in the middle: seesaw, crowbar, scissors.

Class 2

Load in the middle: wheelbarrow, bottle opener.

Class 3

Push in the middle: tweezers, your own forearm.

7 · Try it yourself

Lever hunt

Find 5 levers at home. Tap the button each time you find one.

Build it

The lever kit is on its way: a 3D-printed balance beam with weights you can move.

Tell me when it's ready
8 · Next machine · Week 2Pulleys: How one person lifts a car engine Coming next week