Positive and negative integers are commonly used. Examples are:
Q1. The temperature of the propellant gas is an aerosol can is –25° Centigrade. When it was sprayed into the air on a day when the temperature was +20° Centigrade. By how many degrees did the spray increase?
Q2. Mount Everest is 8850 metres above sea level. The Marianas Trench is 2550 metres below sea level. What is the height difference between them?
Q3. I live on the 14th floor of a high-rise building. If I travel down 5 floors, then up 8 floors and then down 15 floors. Where am I?
A1. 25 + 20 = 45° C
A2. 8850 + 2550 = 11 400 metres
A3. +14 – 5 + 8 – 15 = 2nd floor
The image above shows hot water instantly evaporating in mid-air at –40 degrees. Why? At this chilly temperature, the air has zero percent humidity and water will evaporate instantly. However, it is even chillier in space. Absolute zero, the temperature at which there is thought to be no movement of any kind in the universe, is 0° Kelvin or –273° Centigrade. The very chilly average temperature of the universe due to cosmic radiation is 3° Kelvin or –270° Centigrade. If today's temperature where you live is a very comfortable 20° Centigrade, what would this be in degrees Kelvin?
Write these as number sentences and then calculate the answer.
Q1. From the 5th floor of a building, I go down in the elevator 3 floors, up 2 floors and then down 4 floors. Where am I?
Q2. I have $20. I owe my 2 friends $5 each. I then receive $15 from work. How much do I have?
A1. 5 – 3 + 2 – 4 = 0 (Ground floor)
A2. 20 – 5 – 5 + 15 = 25 ($25)
Trick candles, those novelty ones that re-light after you blow them out, contain a small amount of magnesium within the wick. When blown out, the candle's paraffin wax is still hot enough to re-ignite the magnesium which in turn re-lights the candle wick.