Space, Time and Mass: Definition in Physics - QS Study
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Space, Time and Mass in Physics

Classical mechanics is known as Newtonian mechanics. In this mechanics concept of three fundamental quantities have been considered. These are space, time and mass.

(a) Space: According to Newton, space is an absolute quantity which exists in itself. It is not related to any outer or external thing and is not influenced by environment. For example- length of a body does not depend on the motion of the body or observer and is unchanged at rest.

(b) Time: According to Newton tune is naturally an absolute quantity and does not depend on any other outside object and proceeds uniformly. So time is universal and it moves at a fixed rate which does not depend on object or observer. From this we can conclude two things

  1. Whether an observer is at rest or in motion, but in ten al between any two events is same for all observers and
  2. Two events occurring simultaneously to an observer. time will be same to the observer no matter what the state of motion.

(c) Mass: In Newton’s mechanics, mass of a body is a fundamental quantity which is not dependent on its motion and according to the conservation principle of masses, masses of bodies of independent processes; do not change due to action-reaction between two or more bodies within those processes.


Modern concept:

Scientist Einstein proved that the fundamental quantities of classical mechanics change with motion. So the above three quantities are not fundamental.

(a) Space: Length of a body in motion contracts and becomes less than the length at rest which is called length contraction. So, length of a body contracts with motion.

(b) Time: Time span of an event in a static reference will be larger in a frame of reference in motion. This phenomenon is called time dilation. So, with motion time dilation takes place.

(c) Mass: If a body is in motion its mass increases. This event is called relativity of mass or increase of mass due to motion.