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Conduction

Heat and matter · level 3, lesson 2 of 6

A question to start

A metal spoon and a wooden spoon have sat in the same drawer all night, so they are at the same temperature. Why does the metal one feel colder?

The idea

Conduction is heat passing through a material from particle to particle. At the hot end the particles jiggle fast. They bump into their neighbours and set them jiggling, and so on down the line.

hot endcold endheat passes along

Some materials pass heat on well. They are good conductors. Others are poor at it: insulators.

Good conductors Poor conductors (insulators)
Copper, aluminium, steel and other metals Wood, plastic, cork
Stone, glass (fairly good) Wool, foam, feathers
Water (fairly good) Still air

Now the spoons. Both are cooler than your hand. Metal conducts heat out of your hand quickly, so your hand cools fast and the spoon feels cold. Wood takes your heat away slowly, so it feels warmer, even at the same temperature.

Worked examples

1. A pan. Pans are made of metal so heat from the cooker reaches the food quickly. Their handles are plastic or wood so they do not burn your hand.

2. A tiled floor. In bare feet, tiles feel colder than a rug in the same room. Tiles conduct heat from your feet faster.

3. On Mars. A rover's wheels and frame are metal. Heat inside them could leak out fast, so its warm electronics are kept in an insulated box.

Try it

  1. What is conduction?
  2. Why is a saucepan made of metal?
  3. Why does its handle have a plastic cover?
  4. A metal bench and a wooden bench are both at 5 °C. Which feels colder to sit on, and why?
Answers
  1. Heat passing through a material from particle to particle.
  2. Metal conducts heat well, so the food heats quickly.
  3. Plastic is an insulator, so the handle stays cool enough to hold.
  4. The metal bench: it conducts heat out of you faster.

Common mistake

"Metal is colder than wood." Not if they are in the same place. They are at the same temperature; metal only feels colder because it takes your heat away faster.

Where it leads