Here are the 2 situations: Situation A: a person floating in space far away from any mass (i.e. the person is in zero-gravity environment) Situation B: a person undergoes a free-fall from the top of a roller coaster (assuming that there's no air resistance) My question is, would the person in situation A feel differently from the person in situation B? In other words, are these two situations equivalent? My guess is that they are the same, because equivalence principle states that: An inertial frame of reference is equivalent to a freely-falling frame of reference that is in a uniform gravitational field (this is basically what I understand about GR). Can you guys tell me whether I'm correct? Thanks in advance!