Weightlessness is a feeling of nonexistence of ‘weight’ or force. When a person is standing on Earth, there are two types of forces acting upon him namely, the gravitational force and the contact force, which is an externally applied force. The gravitational force acts to pull a person down, whereas the contact force from various surfaces like the ground, a floor, a seat, a bed or a weighing scale pushes him up. To sense the gravitational force, an opposing force like the contact force is needed, without which an individual would feel ‘weightless’.
If this person were asked to climb as high as a satellite’s orbit on a ladder, although Earth’s gravity has a lower effect at this altitude, he would not feel weightless because he is still experiencing a contact force from the ladder. However, if the individual were to jump down from the ladder, he would experience only the gravitational force during the fall. In this situation, the person is said to be in a state of ‘freefall’ in which he does not experience any g-force acceleration and hence feels a sense of weightlessness.
Weightlessness in an orbiting satellite can be likened to that felt during freefall. The only difference is that, in this case, the gravitational acceleration causes a directional i.e. centripetal change in the satellite’s velocity. This makes the satellite constantly accelerate inward as per the principles of circular motion and fall into orbit around the Earth.
Thus, a person in an orbiting satellite would feel weightless because there is no contact force being exerted upon him since everything in space i.e. the individual and the satellite is in a state of freefall. However, the person and the satellite do not fall to the ground because they are moving ‘sideways’ at a given velocity such that when they fall towards the Earth, the planet’s surface curves away from them. In other words, the individual and the orbiting satellite are constantly falling towards the Earth, but never reach there.
Gagnon, Steve. “Questions and Answers.” jlab. Jefferson Lab, n.d. Web. 26 Mar. 2014. <http://education.jlab.org/qa/gravity_01.html>.