According to principle of transmissibility of forces, the effect of a force upon a body is

Answer: Option C

According to the Principle of Transmissibility of Forces, when a force acts on a rigid body, its effect on the body remains unchanged if the point of application of the force is shifted anywhere along the same line of action.

First, understand what a line of action means. It is the imaginary straight line passing through the direction in which the force acts. The principle says that as long as the force is moved only along this line, the external effect on the body does not change.

Here, the term effect on the body refers to the body's tendency to move, rotate, or remain in equilibrium. This principle is applicable only for rigid bodies because rigid bodies are assumed not to deform under force.

For example, imagine pushing a heavy box with a force of 100 N horizontally. If you apply the same 100 N force at another point along the same horizontal line, the box will still move in the same way. Therefore, the external effect remains unchanged.

Now analyze the options:

Option A: Maximum when it acts at the center of gravity of a body
This is incorrect because the principle of transmissibility does not discuss maximum effect or center of gravity. C.G. is unrelated to this principle.

Option B: Different at different points in its line of action
This is incorrect because the principle clearly states that the effect remains unchanged along the same line of action.

Option C: The same at every point in its line of action
This is correct because moving the force anywhere along its line of action does not change the external effect produced by the force.

Option D: Minimum when it acts at the C.G. of the body
This is incorrect because the principle does not mention minimum effect or center of gravity.

Therefore, the correct answer is Option C: The same at every point in its line of action.