Important physical Quantities

Important physical Quantities

It is profitable to give a brief description of the following physical quantities much used in science and Engineering:-

  1. Mass:-- It is the quantity of matter possessed by a body. The SI unit of mass is kilogramme (kg) . The mass of a body is a constant quantity and is independent od place and position of the body. Thus the mass of a body is the same whether it is on earth's surface , the moon's surface , on the top of a mountain or down a deep well               

  1. Force:-  It is thr product of mass (kg) and acceleration (m/s^2). The unit of force is newton (N); being the force required to accelerate a mass of 1 kg through an acceleration of 1m/s^2).

                                                          F= m a newtons
                                              Where m = mass of a body in kg
                                                          a = acceleration in m/s^2

  • Weight:- The force with which a body is attraction towards the centre of earth is called the weight of the body . Now,

                              Force = mass × acceleration. 
  • If m is mass of a body in kg and g is the acceleration due to to gravity in m/s^2 , then
                 Weight , W = m g newtons

  • As the value of g varies from place on earth's  surface , therefore , the weight of the body varies accordingly. However, for practical purposes, we take g = 9.81 m/s^2 so that weight of the body = 9.81 m newtons. Thus if a mass of 1 kg rests on a table , the downward force on the table i.e., weight of thr body is W = 9.81 × 1 = 9.81 newtons.

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