How Do Gears Work?

Step 1 of 5

Teeth make wheels talk to each other.

Two smooth wheels touching would just slip. Teeth lock them together, so one wheel cannot turn without turning the other exactly.

Step 2 of 5

Different sizes turn at different rates.

A gear with 10 teeth driving one with 30 must go round three times to turn the big one once. Count teeth and you know the ratio exactly.

Step 3 of 5

Slower means stronger.

The trade is the same as a lever: going three times slower gives three times the turning force. That is how a small motor moves a heavy load.

Step 4 of 5

A bicycle lets you pick the trade.

Low gear: the pedals spin fast, the wheel turns slowly, and you can climb a hill. High gear: the opposite, and you fly along the flat.

Step 5 of 5

Gears also reverse and redirect.

Meshed gears turn opposite ways, so a gear train can reverse direction. Angled teeth can even turn the motion through 90 degrees — as in a hand drill.

A clock is a gear train: the same rotation, geared down again and again, drives the second, minute and hour hands.