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Keeping warm

Heat and matter · level 1, lesson 4 of 6

A question to start

A coat has no heater inside it. So how does it keep you warm on a cold day?

The idea

Your body makes its own warmth. On a cold day, that warmth slips away into the cold air. A coat, a hat, gloves or a blanket slow it down, so the warmth stays in for longer.

no coatcoat and hat

Thick, fluffy things keep you warmest. They trap lots of air, and still air is good at keeping warmth in. That is why a puffy coat or a woolly jumper is so cosy. Animals do the same with fur and feathers.

On Mars, astronauts will wear thick spacesuits and live in homes with thick walls, and heaters will make the warmth that leaks away.

Worked examples

1. A hat. On a cold day, a lot of warmth leaves through your head and neck. A hat and scarf help.

2. Layers. Two thin jumpers can be as warm as one thick one, because air is trapped between them.

3. A duvet. It keeps your own warmth in all night. It has no heater inside.

Try it

  1. Where does the warmth inside a coat come from?
  2. Why are puffy coats so warm?
  3. How does a bird keep warm in winter?
  4. A cold-box keeps ice cream cold on a picnic. How do you think it works?
Answers
  1. From your own body.
  2. They trap lots of still air, which keeps warmth in.
  3. It fluffs up its feathers to trap more air.
  4. Its thick walls slow down the warmth getting in from outside, just as a coat slows warmth getting out.

Common mistake

"A coat makes heat." It does not. It keeps in the warmth your body makes. A coat on a chair is not warm.

Where it leads