A good conductor of heat allows heat to travel through it quickly.
A good insulator of heat resists the movement of heat through it.
A good insulator of heat and poor conductor of heat are really the same thing!
Here are two investigations about the speed at which heat travels through solid materials.
1. How quickly does heat travel through wood, metal and plastic?
2. How quickly does heat travel through different metals?
To Investigate how quickly heat travels through wood, metal and plastic.
I will need:
1. A container of hot water
2. One piece each of wood, metal and plastic.
3. Some card to hold them and prevent them from touching each other.
4. Some strips of heat sensitive paper or stick-on thermometer strips.
5. A stopwatch.
For a fair test I will need to:
1. Use exactly the same size pieces of wood, metal and plastic.
2. Make sure they dip into the hot water the same amount.
3. Make sure they go into the water at the same time.
I am going to measure:
How long it takes for the heat from the water to travel up to the end of the rods which is sticking out of the container. I will know when the heat has reached the top of the rods because the heat sensitive paper will change colour.
1. Stick a small piece of heat sensitive paper on the end of each rod with cellotape so that it makes the same good contact on the surface of each one.
1. Fit the wood, metal and plastic rods into holes in the card lid.
2. Pour hot water into the container - for safety I have decided to use water at a temperature of 40degC and will half fill the container.
3. Make sure the stopclock is set to zero.
4. Place the lid containing the rods into position on the container and immediately start the clock.
5. Write down the time taken for the heat sensitive paper to change colour for each rod.
Metal rod 52 seconds
Plastic rod no change after 15minutes
Wooden rod no change after 15minutes
The metal rod allows heat to travel through it. We know this because the heat sensitive paper only changes colour when it gets hot so the heat must have travelled from the water all the way up to the end of the rod. We say that metals are good conductors of heat.
It is impossible to say how quickly heat travels in wood and plastic from this investigation because the heat sensitive paper did not change colour and we ran out of time. I think that the wood and plastic must be very bad conductors of heat but we canít tell if one is better than the other.
I noticed that the water in the container had cooled down a lot after 15 minutes so there might not have been enough heat to make the paper change colour.
Perhaps the metal was so good at letting the heat travel into it that it didnít leave enough heat for the wood or plastic.
Improvements to the method of investigation
1. Try using much hotter water but place the container in a tray in case it spills over and scalds someone.
2. Use the same amount of hot water in 3 separate containers and place a single rod in each one.
3. Try using a much larger amount of hot water so it stays hot for longer.
4. Do not touch any of the rods with your hands before you start the experiment or you will warm them up and this would be unfair.
5. If you do touch the rods place them all in the same container of cold water for a few minutes before you start the experiment so they all cool to the same temperature.