Why is there no degree in Kelvin, as in 10 degrees Celsius

A. Generally speaking degrees are just arbitrary units of measurement. So, the point at which water freezes is designated 0 degrees Celsius and the point at which it boils at 100 degrees Celsius. The division is arbitrary; the difference between freezing and boiling point was just divided into one hundred for the sake of convenience.

However if a unit is absolute or measured directly with respect to something else, then the 'degree' part normally isn't used. Temperature is basically a measure of how much energy molecules have and Kelvin is directly proportional to that, zero in the Kelvin scale means absolute zero and not any arbitrary temperature, and Kelvin is the "natural" unit to measure temperature.

Q. Why use Kelvin, what's wrong with Celsius

A. The Kelvin temperature scale includes a greater scope of possible temperatures, from the coldest anything can get, known as absolute zero, as well as extremely hot temperatures. For example the centre of the sun is 14 million k, although there's no limit on how hot something can become.

Q. How cold is absolute zero

A. It's the coldest it can get, -273.15 on the Celsius scale. Absolute zero is the point at which a gas molecule has no energy.

Q. Why is there a limit on how cold something can become

A. Because temperature is basically a measure of the energy and movement of molecules. As something gets hotter its molecules gain energy and move frantically in all directions.

If you heat water in a glass jar eventually the resulting steam will have so much energy that its banging against the jar will cause it to explode. As molecules can always get more energetic, things will just get hotter.

However the opposite happens when something is cooled: its molecules loose energy, moving slower and slower as they do so. As a material freezes and becomes solid, its molecules are no longer moving, and there is no more energy to loose.

Q. Who was Kelvin

A. Sir William Thompson, 1824-1907, otherwise known as Lord Kelvin of Scotland, invented the Kelvin scale in 1848. A temperature measure in Kelvin is denoted by the letter k.

Got a question about how something is quantified Click here to ask.

by Lisa Cardy