Page 171 - Science Coursebook

11.5 Convection

Activity 11.5
Observing convection

SE Your teacher will demonstrate a
convection current rising above a heater
using a paper circle cut into a spiral.
potassium
You will also see how a convection permanganate
current spreads energy through water. crystal
Coloured water is needed to show how

it flows.
Write an explanation of how the
convection current transfers energy
through the water.
warm air

How convection works
Convection can happen in gases or liquids (fluids) – any material which can flow.

Think about air. It is a gas. Its particles are quite far apart and can move about freely.
When air is heated, its particles move faster and they move farther apart. The air
expands.

Now the air is less dense than the surrounding air and it floats upwards. It carries energy
with it.
At the same time, cooler, denser air flows in to replace it.

So convection is the transfer of energy through a fluid when the fluid itself moves.

Questions

2 Explain why convection cannot transfer energy through a solid.
A+I 3 Why does the wind blow? In the past, some people thought it was the trees
moving their leaves that created the wind. How could you convince someone
that this idea is wrong?
A+I 4 Ocean currents help to transfer energy from the tropics to polar regions.
Explain why warm water currents flow near the ocean surface but cold water

currents flow at greater depths.

Summary
• Convection is the transfer of energy through a fluid when the fluid
itself moves.
• Warmer fluid is less dense and so floats upwards through cooler fluid.

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