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Overload and weightlessness

Lessons 29 · 1 lessons · P.Q. Habibullayev, A. Boydedayev, A.D. Bahromov, S.O. Burxonov. Physics Grade 7, revised and enlarged 4th edition. “O‘zbekiston milliy ensiklopediyasi” State Scientific Publishing House, Tashkent, 2017
29

Overload and weightlessness

Textbook: pp. 105–107
GoalCompute weight on an accelerating support; explain overload and weightlessness.
New words
overload · yuklamaweightlessness · vaznsizliklift (elevator) · liftdirection of acceleration · tezlanish yo‘nalishi
Explanation

If the support moves with acceleration, the weight of a body changes. If the support accelerates upward with a (speeding up while rising or slowing down while descending), P = m(g + a): the weight increases — this state is called overload. If the acceleration points downward, P = m(g − a): the weight decreases. If the support moves down with the free-fall acceleration (a = g), P = 0: the body is weightless. In weightlessness the body does not press on the support or pull a suspension, but gravity does not vanish — the body and the support fall freely together. In an orbiting spacecraft everything is weightless because the craft and its contents are in free fall around the Earth (never reaching it because of their horizontal speed).

Worked examples
A lift accelerating upward at a = 2 m/s²: the weight of a 50 kg person is P = 50 · (10 + 2) = 600 N (more than 500 N at rest).
A lift accelerating downward at a = 2 m/s²: P = 50 · (10 − 2) = 400 N.
Class activity

“Lift thought”: the class discusses how a scale reading changes for someone in a lift (start, steady, stop). Safety: never jump in a lift or lean on its doors.

Practice
1
What is overload?
2
m = 60 kg, a lift accelerates upward at a = 5 m/s² (g = 10). P (N)?
3
m = 60 kg, a lift accelerates downward at a = 5 m/s² (g = 10). P (N)?
4
Why are astronauts in orbit weightless although gravity acts on them?