Across empty space: radiation
The Sun warms us every day. But space has almost no air. How does the heat get here?
Step 1 of 4
- The Sun and the Earth.
- Between them is empty space. There is almost no air there.
- Still, the Sun's heat reaches the Earth.
- This way of moving heat is radiation.
The Sun's heat crosses empty space by radiation. No air is needed.
The new word
- Radiation — heat moving with nothing in between. It needs no solid, liquid or gas.
- You feel radiation near a fire, too.
Dark or light?
Some surfaces absorb more heat. Absorb means take in. A dull surface is not shiny.
| Tank surface | Takes in the Sun's heat | The water inside |
|---|---|---|
| dark and dull | more | gets warmer |
| light and shiny | less | stays cooler |
The rule
Heat can move with nothing in between. This is radiation. It does not need air. Dark, dull surfaces take in more of it than light, shiny ones.
Now try it. Pump out the air. Then block the lamp with a card.
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