Temperature is measured with an instrument called a thermometer ('thermo' means heat). It is important to understand that ‘temperature' and 'heat' are not the same thing. Heat is a form of energy. We can speak about a quantity, or amount, of heat or energy. But we do not speak of an ‘amount' of temperature.
Temperature measures how hot or cold a substance is.
Temperature is not a form of energy, but energy is needed if we want to raise the temperature of something.
Think of a cup of water (about 250 ml, in other words, a quarter of a litre) at 90 ° Celsius. That is very hot-nearly boiling. Think also of a bath full of water-perhaps 60 litres-at 50 ° Celsius. This is a nice, comfortably warm temperature to bath in. Which contains more heat, the cup of water or the bath of water? The answer is that the bath contains much more heat, even though the water in the cup is much hotter. Remember that heat is a form of energy. You would need to put a lot of heat into 60 litres of water to raise its temperature from, 20 ° Celsius to 50 ° Celsius, for example.
With only 250 ml of water, you would need much less energy to raise its temperature from 20 ° Celsius to 50 ° Celsius-or even 90 ° Celsius-because there is so much less water that needs to be heated.
Imagine you tried to heat the bath of water by lighting a candle under it. How many candles would you need to add so much heat to the bath?
Very many! But you would be able to heat a cup of water from 20 ° Celsius to 90 ° or even to boiling, with only one candle.
Temperature (0) is measured in Kelvin (K) in the SI system, but we often talk about temperature in degrees Celsius (° C). Temperature is not a form of heat, but it is a measure of 'state'. It is a measure of the 'condition' or the behaviour of the atoms and molecules making up a substance. We could say temperature is a measure of how 'excited' the molecules are. When we heat a substance (that is, increase its temperature), the energy we put in causes the atoms and molecules to move more quickly. This type of movement is called 'vibration' or 'random motion'.
