Weight is the force exerted on an object by gravity. It is a force, measured in newtons. Mass is a measure of the amount of matter in an object, measured in kilograms. The two are related by the equation W = mg, where W is weight, m is mass, and g is the acceleration due to gravity. On Earth, g is about 9.8 meters per second squared. So a 10-kilogram object weighs about 98 newtons. On the moon, g is about 1.6 meters per second squared. The same object weighs about 16 newtons. Its mass is still 10 kilograms.

Weight is not the same as mass. Mass is an intrinsic property of an object. Weight depends on the gravitational field where the object is. An astronaut weighs less on the moon but has the same mass. Weight is a vector, pointing toward the center of the gravitational body. It is what we measure with a scale. But a scale actually measures the normal force, the force the scale exerts to support the object. In an accelerating elevator, the scale reads differently because the normal force changes. That is why you feel heavier when an elevator accelerates upward. Weight is a force, and forces cause acceleration. That is why objects fall when dropped.

Weight facts

• Definition. Force of gravity on an object.
• Unit. Newton (N).
• Formula. W = mg.
• Earth. g = 9.8 m/s².
• Moon. g = 1.6 m/s².

Weight is not the same as mass. Mass is intrinsic. Weight depends on gravity.