Grade 5 · Unit 3: States of matter
Who invented the temperature scale?
Galileo, Fahrenheit and Celsius – the story of measuring hot and cold.
Feeling is not enough
Put one hand in cold water and one in warm water, then both in lukewarm water. One hand feels warm and the other feels cold! We need a thermometer to measure temperature accurately.
This experiment shows that our senses compare temperatures rather than measure them. Scientists need instruments to measure accurately.
Galileo’s thermoscope
About 400 years ago, the Italian scientist Galileo made a thermoscope. Water in a tube went up and down as the air in a bulb warmed and cooled. It showed changes in temperature, but had no numbers.
Galileo also made telescopes and studied falling objects. He showed that careful measurements can test ideas.
Fahrenheit and Celsius
In 1714, Daniel Fahrenheit made a mercury thermometer with a temperature scale. On his Fahrenheit scale, water freezes at 32 and boils at 212. In 1742, Anders Celsius made a scale from 0 to 100 between freezing and boiling water. Today scientists, and most countries including Bangladesh, use the Celsius scale.
Celsius first put 100 at freezing and 0 at boiling! After he died, other scientists turned his scale the other way round.
Thermometers today
Liquid thermometers use coloured alcohol that rises as it warms. Digital thermometers use electronics and show a number on a screen. Normal body temperature is about 37 °C.
Infrared thermometers can measure temperature without even touching – they detect the heat given out by your forehead.
What I learnt
- I know that thermometers measure temperature accurately.
- I can describe how the temperature scale was developed.