# 1.9. Measuring time

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We usually tell the time of day using watches and clocks. You might also be able to think of other pieces of equipment, such as a sundial. We use clocks, watches, calendars, etc. to measure time.

**Analogue and Digital clocks**

**Telling the Time**

The following conversions are useful when working with time:

- 1 minute = 60 seconds
- 1 hour = 60 minutes = 3600 seconds
- 1 day = 24 hours
- 1 week = 7 days
- 1 year = 365 1/4 days (for the Earth to travel once around the sun)

In practice, every three calendar years will have 365 days, and every fourth year is a “leap year”, which has 366 days, to make up for the extra quarter day over four years. The years 1992, 1996, 2000, and 2004 are all leap years. This gives us a total of 52 complete 7 day weeks in each calendar year, with 1 day left over (or 2 in a leap year).

The year is divided into 12 months, each of which has 30 or 31 days, except for February, which has 28 days (or 29 days in a leap year).

**Measuring speed**

To measure speed, we need to know the distance and the time it took to travel from one place to another. We can then calculate the speed, by using a formula:

Average Speed | = | Distance |

Time |

Example: It is about 360km from Johannesburg to Pholokwane. If the trip took 5 hours to complete, what was the average speed at which your car travelled?

Average Speed | = | Distance | = | 360km | = | 72 km per hour |

Time | 5 hours |

**Measuring temperature**

In winter we’re used to hearing that the temperature has fallen below zero. A temperature of **-4** can be said as **minus four** or **negative four**. Usually when we’re talking about the weather it would be said as ‘four degrees below zero’, ‘four degrees below freezing’, or simply as ‘minus four degrees.’

Temperature is expressed in degrees Celsius in the metric system.

- The boiling point of water (at sea level) is 100°Celsius, or 100°
*C*. - The freezing point of water (at sea level) is 0° Celsius.
- A hot day is about 30° Celsius.

**Reading temperature scales**

Most thermometers (temperature measurers) show the temperature marked on a scale. Each division on the scale represents the same number of degrees.

The first thing to do when you read a thermometer is to check the scale. The three thermometers shown above use different scales.

- Each division on A represents one degree. It is showing 6ºC.
- Each division on B represents two degrees. It is showing 8ºC.
- Each division on C represents five degrees. It is showing 50ºC.