Short Notes:

Objects or people, like the bouncing astronaut, weigh less on the Moon than on Earth because of the Moon's weaker gravitational field. Gravity is a basic force of attraction that is spread throughout the cosmos and acts on all physical objects. The gravitational attraction between any two objects, for example a planet and a person, can be determined by knowing the mass of each item and the distance separating them. Mass, which remains constant, is a measure of the amount of matter an object contains. Weight, on the other hand, is a measure of the force of gravity on an object. The stronger the gravitational field, the greater an object's weight will be and the faster the object will be accelerated; the weaker the field, the less an object's weight will be and the less acceleration it will experience. Since gravity fields vary with the size of the objects they surround, it follows that the weight of an object is not a fixed quantity.

Click here for a Flash presentation on gravity.