Basic science: understanding numbers

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# 3.5 Negative numbers

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#### Transcript

The Celsius scale, also known as the centigrade scale, is commonly used to measure temperatures. The scale is based on the temperatures which control the physical state of water, with zero degrees Celsius being the temperature that ice melts. In other words, when water changes from a solid to a liquid state. And 100 degrees Celsius being the temperature at which water boils, and therefore changes into a gas state.
However, the Celsius scale is not limited to this range. For example, the temperature of the Sun is about 5,500 degrees Celsius. And most home freezers are set to around minus 18 degrees Celsius. This means that the temperature of your freezer is 18 degrees less than zero.
The range of temperatures of Earth varies greatly, from warm desert areas around the Equator, to frozen continents at the poles. The tourist, travelling to some iconic places around the globe, might experience temperatures like 10 degrees Celsius in London, England, minus five degrees Celsius at Niagara Falls in Canada, 40 degrees Celsius at the pyramids in Egypt, minus 30 degrees Celsius in Antarctica, and five degrees Celsius in Machu Picchu in Peru. Our tourist experienced a total range of 70 degrees Celsius during his trip, from minus 30 degrees in Antarctica to 40 degrees in Egypt.
These temperatures are not even the hottest or coldest ever recorded on Earth. On the 10th of July, 1913, Furnace Creek in California reached a sweltering 57 degrees Celsius, making it the highest recorded temperature on Earth. And in August 2010, a satellite recorded that the temperature in Antarctica had reached a chilly minus 94.7 degrees Celsius.
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Intuitively you might consider zero as the lowest possible number, there can’t be anything less than nothing, right? Numbers below zero seem unnatural, or complicated to understand.

The video uses temperature to illustrate that negative numbers are not uncommon and are used all the time. Negative numbers are written with a minus symbol in front of them. For example, a normal household freezer is often set to -18 ˚C (or 18 degrees below zero).

## Activity 3.2 Temperatures and negative numbers

Timing: Allow about 15 minutes

There is a wide range of temperatures that might be experienced by visiting different countries. The temperatures of the five countries in the video were all different, with two below 0 ˚C.

• How hot or cold does it get where you live?
• Where are the hottest and coldest places you’ve visited?
• Can you think of any other everyday situations where you use negative numbers?
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