Question

what information is needed to calculate an object's weight ?

Answer 1

Weight is defined as the force of an object due to gravity.

We know from Newton's First law, that force is proportional to mass and acceleration.

The cool thing about gravity is that the acceleration of any object in a gravitational field is constant in the absence of other forces. For example, we have the classic dropping a hammer and a feather on the surface of the moon. Remember that the moon has no atmosphere so air resistance doesn't slow the feather like on earth. If we drop both of these objects as the same time on the moon, both hit the floor at the same time. This means that gravity exerts the necessary force required to accelerate an object. (You can view a video of the feather and hammer drop here: http://en.wikipedia.org/wiki/Gravitation )

This being said, the weight of an object depends on the objects mass and the gravitational field is in.