Concept:Weightlessness occurs when there is no contact force (normal reaction) supporting the body, even though gravity is still acting.
Explanation:On the International Space Station, both the astronaut and the station are in continuous free-fall towards Earth.
They accelerate downward at the same rate due to gravity (
g).
Hence, the astronaut does not press against any surface, so the normal reaction from the floor is zero.
This zero normal reaction creates the sensation of weightlessness.
The gravitational pull of Earth on the astronaut is not zero; it provides the centripetal force for orbit.
The astronaut’s acceleration is not zero; it is the centripetal acceleration (
a=g at that orbit).
The space station does not apply a centrifugal force; centrifugal force is a pseudo-force in a rotating frame, not a real force here.
Thus, the correct explanation is that the normal reaction of the space-station floor on the astronaut is zero.
Answer:Option B: Normal reaction of the space-station floor on the astronaut is zero.