1.1 Negative numbers on a thermometer
As you have already seen, the common unit that is used to measure temperature is degrees Celsius (°C). You can check the temperature of a fridge or freezer using a special thermometer that shows the temperature between about –30 ºC and +40 ºC. Normally you don’t usually include the plus sign though, as it is assumed that any number without a negative sign is positive. On the thermometer here, the marks above each of the small divisions represent one degree C. This means that the temperature recorded above is –4 ºC. You can see on the thermometer that the temperature increases to the right and decreases to the left.
Use this thermometer to answer the questions in your first activity of the week.
Activity 1 Freezer stars
On the thermometer in Figure 3, what is the temperature range that corresponds to two stars and three stars? Think about what is the most sensible way to show these ranges – that is which number should come first?
The two stars symbol corresponds to a temperature range from –18 ºC to –8 ºC.
The three stars mark from –30 ºC to –18 ºC.
You may be wondering if negative numbers play any other role in everyday life, and why they might be useful to get to grips with. There are a few examples to look at in the next section.