One loop switches another

Ask while they play

The light's battery was unplugged. The little switch still moved. What did the signal battery do?

Spot it at home

• A car's start button: a small switch tells a relay to send big power to the starter motor. A lift button: a small press, a big motor.
• A washing machine or dishwasher: its small control board uses relays to switch the big pump and heater on and off.
• Smart plugs and timer switches: a tiny signal works a relay inside to turn a lamp on.

What small thing tells something big to turn on?

How it helps a robot

• A robot's brain only makes tiny signals. A relay lets one tiny signal switch on a big motor, a pump or bright lights.
• The motor gets its own battery, so it can't drain or damage the brain.

Talk about it later

Why not wire the button straight to the big motor?