A body at rest on the surface of the Earth (or any other planet) will require a force to counteract the gravity acting on it, and its resistance to this force is termed its weight (which is broadly dependent on the amount of matter it contains). More generally, any body will resist forces working to change that body's acceleration, and this resistance to this change in acceleration is termed the body's mass.

Mass, which is generally measured in kilogrammes, is an important determining factor in determining a body's gravitational field, with the strength of a body's gravitational effects on other bodies being directly proportional to its mass.


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