Energy
Heat transfer in nature
Tell conduction, convection and radiation apart by what the particles do, explain land and sea breezes, and follow water from the sea to an aquifer.
Sit by a fire on a cold evening and heat reaches you three different ways at once. The metal poker resting in the flames grows hot along its whole length. The smoke goes up rather than sideways. And your face is warm although nothing whatever is travelling between you and the fire except the heat itself. Those are the three ways heat moves.
The three ways, told apart by the particles
In conduction, a heated particle hands the heat on to its neighbour and stays where it is — this is how heat crosses a solid. In convection, the heated particles themselves travel, carrying the heat with them — this is how liquids and gases heat up. In radiation, heat crosses on its own with no particles involved, which is why it can cross the emptiness between the Sun and the Earth.
Have a play
Four pins are stuck along a metal strip with wax, and one end of the strip is heated. Here is the strip, pin by pin.
Tap any part of the picture.
Worked example
A paper cup is hung upside down on one end of a balanced stick, and a candle is put underneath it. The cup rises. Why?
Look at what the candle is heating. It is not touching the cup — it is heating the air below it.
Whatever lifts the cup has to be the air, since that is the one thing the flame is in contact with.
Try it together
Work out why the wind at a beach turns round between afternoon and midnight.
Two bowls, one of soil and one of water, left in the Sun, are what settles this.
1.After twenty minutes in the Sun, which of the two has risen further in temperature — the soil or the water?
Have a go
Have a go on your own. Water does not leave the ground from rivers and lakes alone — plants and trees give it off too. What is that process called?
Ready to practise?
Eight questions on what you have just read. Nothing is timed, and you can play as many times as you like.