Fundamentals And Derived Quantities And Units SS1 Physics Lesson Note

Measurements play an important role in Physics. A unit has to be defined before any kind of measurement can be made.  Different systems of units have been used in the past. These include the foot-pound second (FPS) system, the centimetre gramme second (CGS) system, and the metre kilogramme second (MKS) system. The new system which has now gained universal acceptance is the system of interop national units, usually called S.I. units.

Physical quantities are often divided into fundamental quantities and derived quantities.

FUNDAMENTAL QUANTITIES: 

These are the basic quantities that are independent of others and cannot be defined in terms of other quantities.

They are the basic quantities upon which most (though not all) quantities depend.

FUNDAMENTAL UNITS: these are the basic units upon which other units depend. They are the units of the fundamental quantities.

The three most important basic quantities in Physics are length, mass and time.

Length may be defined as the extent of space or distance extended. 

Mass is commonly defined as the quantity of matter or material in the body. 

Time is defined as that in which events are distinguishable before or after. Examples of fundamental quantities and their units are shown below:

DERIVED QUANTITIES AND UNITS

Derived quantities and units are those obtained by some simple combination of the fundamental quantities and units. They are dependent on the fundamental quantities and units. Some examples of derived quantities and units are shown below:

The unit of volume is obtained by multiplying three lengths m x m x m = m3 pronounced CUBE METRE or METRE CUBED. Density is the ratio of mass and volume therefore the unit of density is kg/m3 or kgm-3 pronounced KILOGRAMME PER METRE CUBED.

Differences Between Fundamental and Derived Units

Dimensions of Physical Quantities 

The dimension of a physical quantity is the way it is related to the quantities of mass, length and time. The dimension of unit mass is M, for unit length, L and for unit time T. See the table below:

ASSIGNMENT 

1. State the dimension of the following quantities;

(a) Acceleration (b) pressure (c) density

2. From the following quantities given below, list out the derived and fundamental quantities in a tabular form: Velocity, mass, weight, length, volume, density, torque, speed, acceleration, power, energy, temperature, heat capacity, electric current, relative density