When a body of mass m is placed on a weighing machine which is placed in a lift, then actual weight of the body is mg, this acts on a weighing machine which offers a reaction R given by the reading of weighing machine. The reaction exerted by the surface of contact on the body is the apparent weight of the body.

Cases: 1. When lift is at rest then velocity v = 0 and acceleration a = 0

so, R - mg = 0 ⇒ R = mg

Therefore, appreant weight = actual weight

2. Lift moving upward with constant velocity

v = constant and a = 0
so R - mg = 0 ⇒ R = mg

Again appreant wieght = actual weight

3. Lift accelerating upward with acceleration 'a'
R- mg = ma ⇒ R = m (g+a)

Apparent weight > Actual Weight

4. Lift is accelerating downward with acceleration 'a' :

mg - R = ma ⇒ R = m (g-a)
Apparent weight < actual weight

5. Lift accelerating downward at the rate of 'g'

if a = g
R = m (g-g)
R= o
Apparent weight = 0
= Weight less ness

Thus when an object is in free fall it is weightless and this pheno-mena is called weightlessness.