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use a thermometer.We can feel how hot or cold something is. However, sometimes things are
just too hot or cold for us to feel safely. At other times we need to know
exactly how hot or cold something is.
When we need to measure temperature correctly we need to use an
instrument called a thermometer. This measures temperature in degrees
Celsius [sometimes called centigrade] or degrees Fahrenheit.
There are different types of thermometers for different situations. A
medical thermometer, for example, needs to be very accurate. It measures
in fractions of degrees. When we are ill, even tiny changes in temperature
are important.
Some thermometers use a liquid that moves up a very fine glass tube. Most room thermometers, and outdoor
thermometers are like this. The liquid is either mercury [ which is poisonous] or coloured alcohol. As liquids
get warmer they expand [get bigger], and move up the tube. Water expands too, but not as much as alcohol
and mercury.
Thermometers that might be used by small children are not made of glass. They use a digital display which
lights up the temperature. Inside the displays are chemicals that change colour according to the temperature.
