Heat walks along

The idea

Conduction is heat transfer from the hotter part of an object to the colder part: each heated particle passes heat to its neighbour while the particles stay in place; in solids, heat is transferred mainly by conduction.

Pins on a strip

Pema and Palden fix four pins with wax along a metal strip. A candle is lit under one end. (A teacher or adult does this. You will watch an animation.)

Which pin do you think falls first?

• The pin nearest the flame
• The pin farthest from the flame
• All the pins at the same time

Light the candle

Press the button. Watch the pins and the little particles of the strip.

One particle tells the next

The pin nearest the flame fell first. Then II, III and IV. The heat went along the strip. The particles did not walk anywhere. Each hot particle passed heat to its neighbour.

Conduction is heat transfer from the hotter part of an object to the colder part: each heated particle passes heat to its neighbour while the particles stay in place. In solids, heat is transferred mainly by conduction.

• Pin | When it falls
• I (nearest the flame) | First
• II | Second
• III | Third
• IV (farthest) | Last

Notes

Conduction is heat transfer from the hotter part of an object to the colder part: each heated particle passes heat to its neighbour while the particles stay in place. In solids, heat is transferred mainly by conduction.

Check yourself

In conduction, what do the particles of the strip do?

Why did the pin nearest the flame fall first?

Heat travels in conduction from …

In which kind of material is heat transferred mainly by conduction?

• They run from the hot end to the cold end. In conduction the particles do not move away from their positions. Only the heat travels.
• They stay in their places and pass heat to their neighbours — correct. Yes!
• They leave the strip as smoke. The strip stays whole. Its particles stay in place.
• It was the heaviest pin. All four pins were the same. The heat reached the nearest one first.
• The flame pushed it down. The flame did not touch the pins. Heat travelled along the strip and melted the wax.
• The heat reached it first and melted the wax — correct. Yes!
• the hotter part to the colder part — correct. Yes!
• the colder part to the hotter part. Heat flows from hot to cold, not the other way.
• one place to another by the particles moving. That is not conduction. In conduction the particles stay where they are.
• Only in empty space. Empty space has no particles to pass heat on. Solids do it by conduction.
• Solids — correct. Yes!
• Only in smoke. Smoke is a mixture of hot gases and tiny solid particles. Solids transfer heat mainly by conduction.