The international system of units (SI units).


The international system of units  (SI units) or the metric system has seven base units.  All other units in this system are derived from these seven base units.  For phys101, we will deal with only three base units, namely,

Quantity Unit name Unit Symbol
Length meter m
Time second s
Mass kilogram kg

Example: In the SI unit, force is measured in Newton N.  Express N in terms of  the base unit.


Any formula relates force to the base quantities can be used.  For instance, we may use the second law of motion

F = ma.

Here m is the mass and a is the acceleration.  We  know a has a unit of m/s2


N = kg m/s2.