Is there gravity in the Space Station?
This is part of a series on common misconceptions.
Is this true or false?
There is no gravity inside space stations or artificial satellites.
Why some people say it's true: Astronauts fly inside satellites.
Why some people say it's false: Earth pulls the satellite and the people inside it.
The statement is \( \color{red}{\textbf{false}}\).
Explanation 1:
The main confusion here is that the satellites need earth's gravitational pull to rotate, but the astronauts appear to be flying inside the satellite. This gives an illusion of zero gravity inside satellites. This illusion occurs due to the fact that the motion is relative. In the frame of the satellite, the astronauts appear standing still in the air without any support, but in the frame of the earth, they are revolving around the earth with satellite. Just as a satellite needs the gravitational pull to revolve around the earth, so do the astronauts and everything else in the satellite. This implies that there is the gravity of the earth present inside the satellite.
Explanation 2: The illusion of zero gravity inside the satellite can be explained in one more way. The people inside a satellite feel weightless due to the pseudo force. As the satellite is falling freely towards the earth, its acceleration is equal to the acceleration due to gravity at that point. Due to this, in the frame of the satellite, the people and the objects inside satellite feel a pseudo force. This pseudo force is equal and opposite to the gravitational pull, and thus net force becomes zero.
The same phenomenon can be seen in a freely falling lift. Suppose a person is standing in a lift which is falling freely. He takes his phone and releases it. In ground frame both the person and the mobile phone fall freely under gravity. Both moves in the downward direction with the same acceleration. For the person, the mobile phone always remains in front of him and it will appear as flying in the air with respect to the lift.
Query: If a person stands on a weighing machine inside a satellite, the weighing machine will show zero reading. Does that not imply that the gravity inside the satellite is zero?
Reply: That is true that the reading of weighing machine is zero, but that does not imply that the gravity is absent. The person standing on the weighing machine is accelerated towards earth. The weighing machine is not opposing him, as it is also falling with him, with the same acceleration. As there is no normal reaction applied by the weighing machine, its reading is zero.
Query: In the frame of the satellite, the gravitational force felt by any object is zero. Does that not imply that there is no gravity inside the satellite?
Reply: As explained in the second explanation, in the frame of the satellite, the gravitational force is cancelled by the pseudo force. The satellite is accelerated, and thus it is a non-inertial frame of reference. Thus, a pseudo force has to be applied on the object. As the satellite is accelerated towards the earth, the pseudo force will be applied away from the earth. This pseudo force cancels the gravitational force acting on the objects inside the satellites.
See Also