How the weight of a body depends on the type of motion
The weight of a body is the force with which it acts on a support or suspension; it equals the support’s reaction force N in size and is opposite in direction (third law). At rest or at constant velocity P = mg. If the support (a lift) accelerates downward with a, then mg – N = ma, so P = m(g – a); if it accelerates upward, P = m(g + a). If a = g and directed downward, then P = 0 – weightlessness: the body does not press on its support; free-falling bodies, orbiting satellites and the people inside them are in this state. The load factor n = P/(mg) = 1 + a/g (n > 1 for upward acceleration is overload): it is several times larger in a rocket launch and for pilots. On a curved path weight changes too: at the top of a convex bridge P = m(g – υ²/R), at the bottom of a dip P = m(g + υ²/R). If the acceleration is purely horizontal, the vertical weight does not change.
In class, from memory: recall moments on a swing or in a lift when you felt “lighter” or “heavier”, note in a table when each happened and explain them with P = m(g ± a). Do not try any risky jumps or experiments.