Units of Time

Study Notes

Units of time are standards used to measure intervals, and a duration or amount of time is expressed using the most appropriate unit of time.
The International System of Units (SI) defines the second as the base unit of time.
There are very small units of time (e.g., seconds) and very large units of time (e.g., years).

Measuring of time started over 30,000 years ago, using the patterns of the moon, shadows of the sun, and the placement of the stars in the sky.
Sundials were used to determine the time of day based on the shadow formed from the sun.
As civilization and technology advanced, standard units and clocks made it easier to measure time.
Time is now measured based on the vibrations of the cesium-133 atom.

Second: base unit of time, used for very small intervals of time (e.g., blinking, breathing, snapping)
Minute: larger than second, smaller than hour, used for small intervals of time (e.g., drinking coffee, taking a walk, boiling water)
Hour: largest unit of time, used for large intervals of time (e.g., baking a cake, studying)
Day: made up of 24 hours, used for events that take a few days (e.g., hearing back from an interview)
Week: made up of 7 days, used for events that occur weekly (e.g., using products once they are open)
Month: made up of 30 or 31 days (February is 28 or 29 days), used for events that occur monthly (e.g., salaries being credited)
Year: made up of 365 days (366 days in a leap year), used for events that occur annually (e.g., birthdays)

Conversion of units is necessary to express time in the most appropriate unit.
Converting units can happen from smaller to larger units or vice versa.
Examples of conversion:
- 1 minute = 60 seconds
- 1 hour = 60 minutes
- 1 hour = 3600 seconds
To convert a larger unit to a smaller unit, multiply; to convert a smaller unit to a larger unit, divide.

Convert 720 seconds to minutes: 720 / 60 = 12 minutes
Convert 18 minutes to seconds: 18 x 60 = 1080 seconds
Convert 185 minutes to hours and minutes: 185 / 60 = 3.05 hours, 0.05 x 60 = 3 minutes
Convert 20 days to hours: 20 x 24 = 480 hours
Convert 7893 seconds to hours, minutes, and seconds: 7893 / 3600 = 2.1925 hours, 0.1925 x 60 = 11.55 minutes, 0.55 x 60 = 33 seconds