What is pseudo force?

Pseudo force is a non real force

Consider an example that a person is coming down in a lift for a person inside the lift would say that two forces are acting on him 1. Gravitational force 2. Reaction force from lift Which r equal in magnitude cancelling each other keeping man at rest

But from other frame of reference such as from outside the lift u will say that the person inside the lift is accelerating downward . So according to classical mechanics u need a force to cause that . Here we r disscussing that pseudo force.

Mathematical formulatio.n: R force upward and mg downward also acceleration is downward So R-mg equals ma This ma is actually pseudo force