Gravitational Force (Weight)
Forces and Motion


Teaching Guidance for 14-16 PRACTICAL PHYISCS

An object in free fall is said to be ‘weightless’ but is better described as ‘apparently weightless’.

Questions about weightlessness are likely to come up when discussing satellite motion. In free fall, no forces other than gravity act. To someone in a satellite, or (hypothetically) in an ordinary lift after the cables have been cut, objects appear to have no weight. Something placed in mid-air will just float there. Video clips of astronauts show this vividly.

A stationary observer watching from outside the satellite (or lift) will see all objects falling in exactly the same way. They are all in free fall.

An object can only be truly weightless if there is no gravitational field. This would have to be infinitely far away from any other body. Or it could be at a point between two bodies, such the Earth and the Sun, where the pull of the Earth exactly balances the pull of the Sun. Or at the centre of the Earth, where an object would be pulled equally in all directions.

Gravitational Force (Weight)
is a feature of the Rigid Body Model
is a special case of Force
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