One feels heavier in a lift when the lift

The sensation of weight in a lift is determined by the normal reaction force (apparent weight) exerted by the floor. When a lift is stationary or moving steadily (constant velocity), the acceleration is zero, and the apparent weight equals the true weight (mg). However, when a lift just begins to go up, it undergoes upward acceleration. According to Newton's Second Law, the net force is F = N - mg = ma, leading to a normal force N = m(g + a). This increase in the normal force makes the person feel heavier. Conversely, moving down steadily results in no change in weight, and descending freely leads to weightlessness as the normal force becomes zero. Therefore, the feeling of being heavier occurs specifically during upward acceleration, which happens when the lift just begins its ascent.