Physical Quantities Physics Notes
Physical Quantities:
A physical quantity is a quantity that can be measured and expressed in numbers and units.
For example: Mass, length, time, force, velocity etc.
Physical quantities are of two types:
1. Fundamental quantities: Fundamental units are those units, which can neither be derived from one another nor can they be further resolved into any other units. The quantities mass, length and time are called fundamental physical quantities and their units are known as fundamental units because:
- Mass, length and time can not be obtained from one another.
- All other physical quantities in mechanics can be – obtained from them.
2. Derived quantities: The units of all such physical quantities, which can be expressed in terms of the fundamental units of mass, length and time are called derived units. For example force, work, power, energy, pressure, momentum, acceleration, density etc. are all derived units and they can be obtained by writing their defining equations in terms of fundamental physical quantities. To explain, let us consider the defining equation of speed,
we know that:
Speed = \(\frac{\text { Distancecovered }}{\text { Timetaken }}\)
So, unit of speed
= \(\frac{\text { Unitof distance i.e.length }}{\text { Unit of time }}\)
= \(\frac{\text { meter }}{\text { second }}\) = m/s