**Introduction:**

When we consider the theory of general relativity, equivalence principle is any of the several related concepts which deal with the inertial mass and equivalence of gravitational. If we consider Albert Einstein’s experiments on the gravitational force, the observation concluded a similar kind of force experienced by an observer in a non-inertial frame and termed as ‘pseudo-force’ as compared to standing on a massive body such as Earth. **Newton’s Equation of motion** for a gravitational field is stated as follows.

**Gravitational Theory – Development:**

In around the seventeen century, a similar concept like Equivalence Principle came into existence when Galileo expressed about it experimentally. He stated that all material objects undergo similar kind of acceleration in a free fall while being in a gravitational field, regardless of their composition or mass. Later, making use of Galileo’s Principle Kepler the knowledge of an Equivalence Principle was showed by describing the concept.

Tests performed in a consistently quickening reference outline with speeding up are indistinct from similar examinations conducted in a non-quickening reference framework which are arranged in a gravitational field wherein the increasing speed of gravity = g = – a = power of gravity field. One method for expressing this above rule of general relativity is to state that gravitational mass is indistinguishable to inertial mass.

One of the outcomes of the rule of identical is that photons consist of force and in this manner, it can be credited an inertial mass and they should likewise consist of a gravitational mass.

Accordingly, photons are ought to be avoided by gravity. They ought to be obstructed in their escape from a gravity field, prompting to the gravitational red move and the idea of a dark gap. It additionally prompts to gravitational focal point impacts.

**Application: **

Equivalence Principle is presently used in three forms namely Galilean (Weak), Strong and Einsteinian.

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