The units of all physical quantities can be derived from the seven basic units. These units are called derived units because they can be derived from the basic units algebraically by multiplication and division. It is frequently necessary to convert one set of units to another.
Some of the Common derived units
| Quantity |
Derivation of the Quantity |
SI Unit |
Symbol |
| Area |
Length square |
m2 |
|
| Volume |
Length cube |
m3 |
|
| Density |
Mass per unit volume |
kg m-3 |
|
| Speed |
Distance travelled per unit time |
m S -1 |
|
| Acceleration |
Speed change per unit time |
m s-2 |
|
| Force |
Product of mass and acceleration |
kg m s-2 |
Newton
(N)
|
| Pressure |
Force per unit area |
kg m-1 s-2 |
Pascal (Pa) |
| Energy, work |
Product of force and distance |
kg m2 s-2 |
Joule (J) |
| Power |
Energy/ time |
kg m2 s-3 or J s -1 |
Wall (W) |
| Electric charge |
Product of current and time |
As |
Coulomb
(C)
|
| Electric resistance |
Potential difference/current |
VA-1 |
Ohm (Ω) |
| Electrical conductance |
Reciprocal of resistance |
AV-1 |
Siemen
(S)
|
| Frequency |
Cycles/sec |
S-4 |
Hertz (Hz) |
