Temperature is a measure of the level of heat. 

We all know what heat feels like.  You probably will say that you also know what cold feels like, but cold is really just the absence of heat.  Temperature measures the level of heat and when the level is very low, we say it is cold. 


What is heat? 

Heat is a form of energy. 

In any object that possesses heat, the tiny particles of which it is made are in a state of vibration, constantly moving against each other

If you touch a piece of hot metal, the vibrations in its molecules, those tiny particles, are transferred to your hand, which feels the heat. 

If we heat a kettle of water, the molecules in the water vibrate more and more violently until they can no longer hold together as water and turn into vapour, or steam. 

If we put water into a freezer, the molecules vibrate more and more slowly and lose their heat until the water turns into ice. 

You can see why we say that heat is a form of energy. 


Temperature and heat 

If you were asked to find out how much heat was in something, you would probably want to use a thermometer to measure its temperature. 

The temperature, however, does not tell us the amount of heat.  It simply tells us the level of heat.  If you take two equal amounts of two liquids such as water and mercury at the same temperature and heat them equally, the temperature of both of them will rise. 

The temperature of the mercury, however, will rise 30 times more than the temperature of the water. 

Whatever liquid you choose, you will find that the same amount of heat will make its temperature rise faster than the temperature of water. 

In other words, water needs to be given more heat in order to raise its temperature.  The opposite is also true; water gives off heat without dropping very much in temperature. 


The temperature of water and our climate 

All day long the oceans of our world are taking in heat from the sun’s rays, absorbing far more heat than any other substance could. 

During the night, when the temperature of the air above the oceans falls, they give some of this heat back to the air.  Heat always flows from the warmer to the cooler substance. 

In the same way, some of the heat which the seas absorb during the summer months is stored and slowly given back in the winter. 

The British Isles, for example, are surrounded by water and the temperatures are much more even through summer and winter than those of places surrounded by land. 

The sea around the British Isles acts like a great hot-water bottle, saving the islands from the extremely cold temperatures of many places in Europe and Asia closer to the equator. 


Measuring the level of heat with a thermometer 

If you are interested in the weather, it is a good idea to keep a weather diary.  Each day write down what the weather was like (wet, dry, windy, sunny, cloudy) and make a note of the temperature.  You should take the temperature at the same time each day. 

For this you will need an outdoor thermometer.  You must hang it in the shade so that the sun’s rays do not touch it.  You are measuring the level of heat in the surrounding air, not the level of heat in the sun’s rays! 

The temperature can be read in one of two scales, the Fahrenheit scale, or the Celsius (sometimes called centigrade) scale. 

The freezing point of water on the Celsius scale is 0 °(written as 0 °C.) and the freezing point of water on the Fahrenheit scale is 32 °(written as 32 °F.) 

If you keep this record for a whole year, you will be able to see what the extremes of temperature are where you stay, that is, what the highest and lowest temperatures are over one year.  The thermometer below is showing the temperature on a warm summer day.  Can you see what the temperature is?