Weight is a measure of the centripetal force, or thrust exerted on, and/or by
objects; bodies, or masses of the particles [atoms and molecules] that
comprise the substances that we call matter; when they are at rest on the
terra firma surface of Earth, or a similar planet.

This force is primarily due to gravitation; where all matter is continuously
gravitating toward a common center of mass; at a rate that varies inversely
as the distance separating them; as well as being affected by the centrifugal
effect due to the planet’s rotation.

That is at Earth’s equator where the rotation is greatest, the centrifugal
effect is greatest, and causes weight to be least there. Weight will also
vary with elevation, and is less on hills than in valleys.

Units of weight are units of force: In the International System of Units (SI),
the “modern” metric system, the unit of force is the newton. In the
foot-pound-second system used in the United States, units of force
customarily include the ounce and the pound. One pound being equal to 4.448
newtons; which is the weight of 0.454 kilogram.

Newton found the “mass” of an object to be equal to it’s “bulk and density,
conjointly”, as well as being the ratio of its weight [w], divided by the
acceleration at which it will free fall [g] at the location where it is
weighed.

He related this “gravitational mass” [w/g] to mass [m] in general as being
equal to “inertial mass” [f/a]; which is the ratio of the net force [f],
divided by the acceleration [a] that it causes _anywhere_, _anytime_: Where
through algebra: f = wa/g, and w = fg/a: Where the mass is incidental; since
it’s just two different ways of saying the same thing: That mass is a ratio
of force to acceleration.

For commercial and everyday purposes, weight is commonly used to mean the
quantity of matter in an object. When people use weight in this sense, they
measure it on weight scales. The kilogram is the SI's base unit of mass;
where one pound is the weight of 0.454 kilogram.

This is a rewrite of the World Book’s article on weight, and in my humble
opinion is considerably truer.

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