Keeping in the heat

Heat can pass through materials. Here is a way to compare how heat passes through a sheet of aluminium, a sheet of paper and a cotton handkerchief. Each cup contains the same volume of water and all the water is at the same temperature. A thermometer is placed on each material and after a few minutes the temperature of the top of the material is taken.
The length of the liquid column in the thermometer shows the temperature of the liquid. The thermometer with the longest liquid column shows the highest temperature and the thermometer with the shortest liquid column shows the lowest temperature.

Which would be best for keeping the heat in an electric kettle while it boils - a metal kettle or a plastic one?
Metal is a better conductor of electricity than plastic, so the metal one would lose more heat while it was heating water than a plastic one.

Where does the heat in our bodies come from?
It comes from the food you eat. The food is a store of energy. The energy is used to keep you warm as well as to allow you to move about and do many other things.
Why do we need to keep warm?
To stay alive our bodies need to be about 37°C. If we get too cold we can die.
How can people live in cold places?


The colder an environment is, the more effort you have to put in to keep warm. There are three things people do to live in a cold climate. First they dress warmly. Secondly they try to live in well-insulated homes. Thirdly they make sure they have enough fuel to keep the heating going in a home.
The smaller the home, the easier it is to keep it warm, so people in cold places often have small rooms. Many have small windows, too, because most heat is lost through the window glass. Double and triple glazing is common.
Most people live in modern-style homes, but older, simpler, kinds of homes were often quite good at keeping in the heat. Even the traditional Arctic igloo, made of snow blocks was good at keeping in the heat. It had a long tunnel to keep out drafts, it was small, and snow (which has a lot of air trapped in it) is a good insulator.


Why is wool so good at keeping heat in?
Wool is made from curly fibres which are also springy. These properties stop the fibres lying very close together when they are spun. There is air in the gaps between the fibres and this stops heat from passing through the wool.
Can air be used on its own to keep heat in?
No. It needs to be kept still. A material needs to be used to trap it. This can be in the form of fibres like wool, or it can be in the form of sheets like the glass in a double glazed window. Plastic foam can also be used in the walls of buildings to help keep the heat inside.

Do animals need to keep warm like us?
Only mammals and birds need to keep warm like us. The rest can survive when their bodies are at lower temperatures. Mammals trap air in their fur, while birds ruffle their feathers.
Does bark keep trees warm?
Yes. It is important for the inside of trees not to freeze. If they did the water in them would turn to ice and damage them. We even use bark from a cork tree to make heat-proof mats to put on tables.
Can materials be grouped according to how heat passes through them?
Yes. Materials like wool and cork which stop heat passing though them are called insulators. Materials which let heat pass through them quickly, like aluminium, are called conductors.