[CHAT/CM-08007] Let's Talk --- Fundamental Interactions

There are four types of fundamental forces or interactions. These are

1. Gravitational Forces
2. Electromagnetic Forces
3. Strong forces which are responsible for binding of a nucleus.
4. Weak forces or the forces responsible for beta decay.

Of these four forces, we experience only the first two type of forces in our daily life. These have characteristic strength, range and other properties. The strong and weak forces have very short range and don’t play any role in mechanics. All the mechanical forces are electromagnetic in nature. So in our discussion in this course we will be concerned about these two types of interactions.

The Newton's laws are valid in inertial frames only. These laws can be used in non inertial frames if we account for pesudo forces. The pseudo force on a body are proportional to its mass.

The electromagnetic forces do not depend on mass, hence the pseudo forces can be differentiated from the electromagnetic forces. It turns out that it is locally impossible to distinguish between gravitational forces and pseudo forces. This is because the both gravitational forces and pseudo forces in an inertial frame are proportional to the mass of the body. In practical terms it means that effect of gravitational forces in a given inertial frame can be reproduced by that coming from pseudo forces in an non inertial frame. So for example, EOM in uniform gravitational field is same as motion in a lift accelerating upwards without any gravitational forces. In his form it is known as Einstein's equivalence principle, and this statement holds for small regions of space. It should be noted that the pseudo forces on a body are always proportional to the mass of a body.