Tulsi Prajna 1990 09

SR No.: 524563
Original Sutra Author: N/A
Author: Mangal Prakash Mehta
Publisher: Jain Vishva Bharati
Publication Year: 1990
Total Pages: 80
Language: Hindi
Classification: Magazine, India_Tulsi Prajna, & India
File Size: 4 MB

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Vol. XVI. No. 2 help of this law of gravitation.
Another important law which was enunciated by Newton was the ‘law of inertia', which stated that a body at rest continues to remain at rest and a body in uniform rectilinear motion continues to be in motion, and a change in the state of rest of motion can be brought only by exerting some external force.' Thus when a body is started or stopped suddenly, a jerk is felt. This is due to the force of inertia.
Generalization by Einstein
As we have seen, in the special theory of relativity, only those systems are considered which are in uniform rectilinear motion. Such systems are also known as 'inertial' systems, i.e. systems in which the law of inertia holds good so that a body not subjected to a force remains at rest or in uniform motion Now, according to the special theory of relativity, in all inertial systems the physical laws have the same form. Einstein extended this principle of equivalence to systems moving in any way, even with accelerated velocity and, in particular, to a special case of accelerated motion involved in the phenomenon of gravitation. Thus, the general theory of relativity states that 'the laws of nature are same for all the systems whatsoever their motion may be.'
Two Imaginary Experiments
Einstein started with the revolutionary idea that the classical picture of a gravitational field is artificial, since it is possible for an observer not to detect such a field at all by choosing a suitable frame of reference. He proved this by two imaginary experiments as follows:
1. Suppose an enclosure (such as an elevator) from which nothing can be knowa of what goes on outside it, suddenly starts falling freely under the action of gravity. (It may be imagined here that the cables by which the elevator is supported, suddenly break). Imagine that there is a scientist inside the enclosure, who performs an experiment of dropping an apple from his hand. To his surprise he finds that the apple instead of falling down to the floor, remains floating in the space. He performs another experiment by throwing a horizontal projectile. Again he surprises to find that instead of traversing a curred path, it goes on moving along a straight line till it strikes against the walls of the enclosure.
Thus, the force which causes apples to fall and the horizontal projectile to trace a curved path, i.e. gravitation disappears for him. In