Hold a mug of hot cocoa and your hands warm up. Put an ice cube in your hand and your hand gets cold. Heat is on the move.
Key idea
Heat moves from warmer things to cooler things, never the other way by itself. It moves three ways: by touching (conduction), by moving air or water carrying it (convection), and by rays through space, like sunshine (radiation).
| Conductors (heat moves through fast) | Insulators (heat moves through slowly) |
|---|---|
| Metal spoons and pots | Wood and plastic handles |
| Aluminum foil | Wool, cotton, a sweater |
| Stone floors | Air trapped in a foam cup or a coat |
Why it works
A metal spoon in hot soup gets hot all the way up because metal passes heat along quickly. A wooden spoon stays cool at the top because wood is an insulator.
Worked example: The sweater test
Does a sweater make you warm by making heat?
- A sweater has no energy source.
- It traps air, an insulator, so your own body heat escapes slowly.
Answer: No: it keeps your body heat in.
Common mistake
Thinking cold "moves in". Your hand feels cold on ice because heat leaves your hand and goes into the ice.
Try it at home
- Wrap one ice cube in a sock or a mitten and leave another bare on a plate.
- Check every 15 minutes. Which melts first? The insulator slows heat from reaching the ice.
Going further. The Laws of Thermodynamics in the Science Lab, and Heat Transfer in Physical Science.