You're bang on there about momentum and inertia, arkain. Mass and velocity is all that the moving object has, so translating from momentum to kinetic energy involves some kind of... I'm not sure how to say this: It's some kind of observational change where we step from a time-based viewpoint to a space-based viewpoint. But let's keep the simple point that colliding objects are in contact with each other for the same length of time. That's the easy way of remembering why momentum is conserved.
Sebby: see TIME EXPLAINED where I describe colour as a perception that isn't real because the underlying property is wavelength. Heat isn't perception, it burns your hand, and is an experience. If we think
Kinetic Theory of Gases the underlying properties are mass and velocity, but if we think
Sunburn and photons the underlying property is momentum. Obviously there's energy in both cases, but whether you say a photon is "made" out of energy is moot. You wouldn't say it was made out of momentum. Oh boy, there are big issues with "things" and "properties". If you add properties to a thing like a string, you get a different thing, like a knot. If you reverse this, at what point does the thing become no thing, and the things that made it a thing turned out to be just the properties you took away? We need a new thread for this, I'm thinking of an essay called... NOTHING EXPLAINED.
