Cool It

Have students work in groups. Young students usually find graduating four cups of water from coolest to hottest relatively easy. Take care that the water is no hotter than about 40°C. Ice cubes can be used to create a water temperature that is close to 0°C. The thermometer is an example of a linear scale and is easily related to the number line.
A good introduction is to give each group of students a thermometer and tell them to find out how it works. Their explanations, although lacking scientific rigour, often reveal that they know that increased height in the column of alcohol means that the temperature is higher. For example, “As it gets hotter, the red stuff gets pushed up higher.”
You will need to tell students that the numbers up the side of the column show the temperature in degrees Celsius and that these temperatures can be written as X°C (for example, 17°C). A simple thermometer can be drawn on card and strips of red stuck on it to show different temperatures. This gives students practice reading the thermometer scale.
Of the cups of water, the hottest cup will cool fastest as the difference between its water temperature and the air temperature is greatest. Eventually, all four cups will end up with a water temperature close to that of the air, though this can take a period of hours.
Once students have some experience with these known temperatures, you can ask them to make up by feel a cup of water with a given temperature (for example, 25°C). You can check their attempts with a thermometer to see how close they got to the target temperature.

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