Heat

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3

Slide 20

Convection

What happens to the particles in a liquid or a gas when you heat them?

The particles spread out and become less dense.

A liquid or gas.

Slide 21

Convection

It is the way in which particles in a GAS or LIQUID move upwards, carrying heat with them

Think about when you boil water, the bubbles move upwards

Or think of a gas heater in the room, the heat rises around the room

Slide 22

Convection

Hot water rises

Cooler water sinks

Convection current

Cools at the surface

Slide 23

Convection

Where is the cooling compartment put in a fridge?

Cooling compartment

It is put at the top, because cool air sinks, so it cools the food on the way down.

It is warmer at the bottom, so this warmer air rises and a convection current is set up.

Slide 24

Should a radiator be called a radiator?

Slide 25

Convection questions

Why are boilers placed beneath hot water tanks in people’s homes?

Hot water rises.

So when the boiler heats the water, and the hot water rises, the water tank is filled with hot water.

Why does hot air rise and cold air sink?

Cool air is more dense than warm air, so the cool air ‘falls through’ the warm air.

Slide 26

Heat Vs Temperature

The temperature of an object tells us how HOT it is

Measured in degrees Celsius - °C

It is NOT the same as heat energy although the two quantities are related. e.g. a beaker of water at 60 °C is hotter than a bath of water at 40 °C BUT the bath contains more joules of heat energy

Slide 27

Heating and Cooling

If an object has become hotter, it means that it has gained heat energy.

If an object cools down, it means it has lost energy

Slide 28

Heating and Cooling cont…

Heat energy always moves from:

HOT object COOLER object

e.g. Cup of water at 20 °C in a room at 30°C - gains heat energy and heats up – its temperature rises

Cup of water at 20 °C in a room at 10°C loses heat energy and cools down – its temperature will fall.

Slide 29

Expansion/Contraction