Standard Units of Measurement (meter, second, kilogram)

The three essential units are the units for mass, length, and time. Mass is understood as the
amount of substance in an object. Its SI unit is kilogram (kg). However, pound and gram are
also used to measure it. We write m = 10 kg to represent an object with mass 10 kilogram.

We can use any of the various units that are currently in use to measure the mass of an object.
However, when masses are added to or subtracted from each other the units must be same
because masses shown in different units cannot be summed or subtracted. For example
masses measured in kg cannot be added to the ones that are measured in gram. What we need
to do in such a case is to convert either the kilogram into grams or the grams to kilograms.
Therefore, conversion of units become important in physics.
1 kg = 1000 g
1 g = 1000 mg
Meter (m) is the SI unit for measuring distance. We represent the length of a 10 meter long
object as l = 10 m.
1 km = 1000 m
1 m = 100 cm
The duration between two events is called time and it could be measured in days, months,
hours and minutes. But the international standard unit is the second. In the old days, the
duration of second is calculated based on the duration of a day. However, today it is measured
by an atomic clock. The second is represented by the symbol s.
1 hour = 60 minutes = 360 seconds
1 year = 365.25 days = 3×10^7 seconds