Astronauts orbiting the Earth often report a sensation of “weightlessness” even though the Earth’s gravitational pull at their altitude is still appreciable.
(i) Define the terms (a) weight of a body and (b) apparent weight as measured by a spring balance.
(ii) Explain clearly, with the help of physical reasoning, why astronauts inside a spacecraft moving in a stable circular orbit experience weightlessness even though the gravitational attraction on them is not zero.
(iii) The spacecraft’s engines are fired in the opposite direction so that its speed is suddenly reduced while it is still at the same altitude. Describe qualitatively what the astronauts would feel immediately after this change and give the reason for your answer.