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Definition of Weightlessness:
Weightlessness is the sensation that is experienced when the only force acting upon an object is the force of gravity.
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Weight or the force of gravity is a non-contact force and can never be felt. Our only sensation of our weight is the feel of a contact force that counteracts or balances our weight. We can feel the normal force of a seat or chair or bed pushing upward on our body. We feel this force nearly 24 hours a day and have a good sense of what it feels like. If this upward force ever becomes greater than its usual value, then you would experience a momentary sensation of weightiness. If this upward force ever becomes less than its usual value, then you would experience a momentary sensation of partial weightlessness. In this question, you are to identify situations which are consistent with feelings of partial weightlessness. You need to identify those situations in which the normal force is less than the usual value. The normal force is not listed in these questions; only the acceleration is listed. So you will need to think about this: When the normal force is less than the force of gravity, in which direction will the object accelerate? If you can answer this question, then you can answer the MOP question. See the Know the Law section if necessary.
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Net Force and Direction of Acceleration
Newton's second law relates the acceleration of an object to the net force exerted upon the object. The acceleration is directly proportional to the net force and in the same direction as the net force.
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