Lever Law

Why it matters

"Give me a place to stand and I will move the Earth" — Archimedes wasn't bragging about muscles. He was bragging about arm ratios.

The idea in plain words

The lever's ledger. Tap the terms.

MA = effort arm ÷ load arm

Crowbar: effort arm 1 m, load arm 0.25 m. Effort to lift 600 N?

150 N — a child's push for a boulder

• class I signature: fulcrum — the pivot — class I keeps it BETWEEN load and effort (see-saw, scissors, crowbar)
• metre: effort arm — fulcrum → effort distance: make it long
• metre: load arm — fulcrum → load distance: make it short
• MA = 1 ÷ 0.25 = 4
• effort = 600 ÷ 4

Predict first

A crowbar's MA gets bigger when you…

MA = effort arm ÷ load arm — pure geometry. Your push decides nothing about the RATIO, only whether you win.

• lengthen the effort arm or shorten the load arm — correct
• push harder
• use a heavier crowbar

What you do

Set the arms so a 600 N rock yields to 200 N or less.

Check yourself

A pair of scissors is a…

The rivet sits between effort (handles) and load (paper): class I, doubled.

A class I lever can have MA less than 1 — when would you WANT that?

Long blades move faster than your fingers: trading force for speed is a feature, not a bug.

To lift with the SAME effort a load twice as heavy, keep the load arm fixed and…

Moments must still balance: double the load needs double the effort moment — stretch your arm, not your muscles.

• pair of class I levers (pivot between blades and handles) — correct
• class II lever
• class III lever
• When you want more SPEED/range at the load, like scissors for cloth — correct
• Never — MA < 1 is useless
• When the load is very heavy
• double the effort arm — correct
• halve the effort arm
• double the load arm