1. A passenger inside a lift experiences only two forces:
- Gravitational force mg directed vertically downwards and
- normal reaction force N directed vertically upwards, exerted by the floor of the lift.
2. As these forces are oppositely directed, the net force in the downward direction will be F = ma – N.
3. Though the weight of a passenger is the gravitational force acting upon it, the person experiences his weight only due to the normal reaction force N exerted by the floor.
4. A lift has zero acceleration when the lift is at rest or is moving upwards or downwards with constant velocity.
5. Thus, a net force acting on the passenger inside the lift will be,
F = 0 = mg – N
∴ mg = N
Hence, in this case the passenger feels his normal weight mg.