How Switched On Are You?

HEAT• Radiation• Reflection• Absorption• Transmission• Conduction• Convection

What do you think the picture is?

Where does our heat come from?• All the heat on our Earth

comes from the sun.• The sun is 6000oC on the

outside and 1 300 000 times the size of Earth.

• So, even though it is about 150 million km from Earth, we still feel its heat.

Why is it always hotter during the day than at night?

How do we want to live?

• We want our houses to be cool in summer when the sun’s heat is at its highest.

• We want our houses to be warm in winter when the sun’s heat is at its lowest.

How well does your house do this without the aid of any heating or cooling devices?

So how does heat get around?

• Heat from the sun reaches Earth through a process called radiation.

• Radiation is the only way that heat can travel when there are no particles, such as the vacuum of space.

• It does this using infra-red rays.

What else can you think of that uses infra-red rays?

Reflection• When the sun’s rays reach

Earth, they can be reflected, as if they were hitting a mirror.

• This can happen before they even reach Earth, if they are reflected back into space by clouds or other particles in the air.

• This can happen when they reach an object that has reflective qualities.

Can you think of any objects that have reflective qualities?

What happens when heat comes to Earth?

• Reflection

• Absorption

• Transmission

Can you think of examples of each of these?

Reflection examplesHumans use the reflection of the

sun’s rays to our benefit in many ways:

• We laminate the windows of our cars and homes to keep the sun’s heat out

• We paint our houses white/light colours to reflect the sun’s heat away

• We buy white cars because they will stay cooler when left out in the sun.

How do you use reflection?

Absorption• When the sun’s rays reach

Earth, they can be absorbed, like a towel soaking up water.

• They can be absorbed by clouds and other individual water droplets in the air.

• They can also be absorbed by the surface of the Earth.

Can you think of examples when the sun’s heat is absorbed?

Absorption examplesHumans use the absorption of

the sun’s rays to our benefit in many ways:

• Pipes used in pool solar heating and solar panels are black to absorb more heat.

• On a cold day we can wear black clothes to warm us up in the sun.

How do you use absorption?

Transmission• When the sun’s rays reach the

Earth, they can be transmitted, and pass through substances.

• They can be transmitted through the surface of the ocean and swimming pools.

• They can be transmitted through the windows and curtains of a house.

Can you think of other substances that the sun’s heat can be transmitted through?

Transmission examplesHumans use the transmission

of the sun’s rays to our benefit in many ways:

• When it is cold we open the curtains to let the sun more easily reach inside

• We like it when the sun enters our pools during the colder months and warms it up.

How do you use transmission?

What happens when heat arrives at a substance?

That depends on whether the substance is a:

• Solid• Liquid• Gas

Can you think of examples of solids, liquids and gases that display these properties?

Solids, Liquids and GasesAll substances are made up of tiny particles.

• Solids have their particles so tightly packed that they can’t move. When heated, the particles can vibrate.

• Liquids have their particles right beside each other, but there is room to move around each other.

• Gases have their particles very spread out, so they are just floating around with lots of space between them.

Which one is which?

Conduction

• When one part of an object is heated, this heat can be passed from one particle to the next inside the object.

• However, the particles must be right beside each other, so conduction works best in solids.

Conduction examples

• A tin roof heats up very quickly due to conduction.

• A tiled roof does not pass on much heat due to its construction.

Can you think of other examples of conduction?

Convection• When one part of an

object is heated, the heated particles move to allow the cooler particles to replace them. This results in the whole substance being heated over time.

• Due to the particles having to move, this works best in liquids and gases.

Convection examples• An electric heater heats the air

around it, this rises and the cooler air replaces it to become heated.

• When it very cold at night, the air just inside a window is also cooled down. Without a curtain, convection would cool down the rest of the room.

• A greenhouse creates a warm environment by allowing heat in, via transmission, and then convection heats up all the air inside, helping plants to grow. Can you think of other examples?

So, how can we make our homes cooler in Summer?

We need to:• Increase reflection on our

windows to prevent the sun from coming inside

• Reduce reflection from cement around the house by planting more gardens which absorb the heat

• Reduce absorption of the sun’s heat on our roof and walls

• Reduce transmission of the sun’s heat through our windows

• Reduce conduction on our roof and other house construction materials

• Reduce the heat that enters our house and therefore reduce convection of this heat

We also need to work out how to do all this using less energy to save us money and to save the environment! Any ideas?

Ah, a nice cool house, naturally…