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Measurement of Mass

When an external force is applied on a body, the force tends to change the state of motion. The body either in magnitude or in direction, while the body opposes any change in its state of motion. The property by virtue of which a body opposes any change in the motion of the body is called the inertia.


Measurement of Mass of a body


If F is applied force and a the acceleration produced in the body of mass m, then

The mass of the body determined in this way is a measure of inertia and is called the inertial mass of the body. The inertial mass of a bus is sufficiently more than that of a cycle, because to produce same acceleration in a bus and a cycle, much larger force (push) is required in the case of a bus.


Inertial Mass


The inertial mass of a body can be measured by an inertial balance. An inertial balance consists of a long metallic strip. One end of this strip is clamped to a table, such that its flat face is vertical, so that it can vibrate horizontally. The other end of the strip supports a pan in which an object, whose inertial mass is be determined, is kept. The metal strip is allowed to vibrate horizontally and time of vibration is noted. The experiment is repeated with other object. The time of vibration depends upon

  1. Length of the projecting part of the clamp
  2. Stiffness of the material of the strip and
  3. Total mass of the pan and the object

Gravitational Mass


The weight of a body is proportional to its mass. The gravitational mass of a body is the mass which determines the gravitational pull due to earth acting on it.

Under the same condition9same place on earth at same altitude), the weights of two objects are proportional to their masses. If W1 and W2 are weights of two bodies placed at same place on earth, then


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