Is mass a property of matter?
Mass can be defined in two different ways: 1. Inertia. This is to say that the more mass something has, the more difficult it is to put in motion or to change its motion. Technically, you multiply mass by velocity to obtain momentum. 2. Gravitational mass. The more mass an object has, the greater the force (called “weight”) a given gravitational field exerts on it. Technically, you multiply mass by gravity to obtain weight. The fact that those two approaches end up defining EXACTLY the same thing is the so-called “equivalence principle” which is the basic tenet of Einstein’s General Theory of Relativity. There is a fine point to be made in distinguishing between ordinary mass (which you may call “rest mass” if you must) as opposed to the so-called “relativistic mass” which appears in the famous equation E=mc^2. Neither concept is strictly reserved to particles of matter (which physicists call “fermions”) as both properties can also be assigned (at least in some cases) to the things whi
