Human beings have been thinking about and counting time for thousands of years. The first time-keeping machines used sand, water or the position of the Sun in the sky to mark out the passage of time. These days, we use clocks and watches for telling the time. But however we do it, our measurement of time is based on the movement of our planet Earth in relation to the Sun.
Numbers are useful for counting and measuring things. We use them all the time, even when we’re not thinking about maths. For example, I use them every day, for telling the time, cooking, exercising and driving my car.
Normally when we count, we start at zero and count upwards in whole numbers: one, two, three, and so on… But what happens if we count down from a bigger number – do we have to stop when we get back to zero?
This question was asked on a cold Winter’s day. The water in the bird bath had frozen and I used hot water from the kettle to thaw it so the birds could drink. When I explained to my 6-year-old that water freezes at zero degrees Celsius, she wondered if that was the coldest that things can get. But it isn’t – in fact some things can get much, much, much colder!
So what happens when things get hot or cold and how do we measure temperature?