3 ms·
You'd still have conservation of momentum; you don't have to have mass (or at least, the kind of mass I suspect you're thinking of) to have momentum.
by EliRivers 8y ago
You'd still have conservation of momentum; you don't have to have mass (or at least, the kind of mass I suspect you're thinking of) to have momentum.
- cm2187 8y agoThanks. I must be missing something. If I have a particle emitted from point A and stopped in point B, travelling between the two at velocity v, and that I can magically change its mass in flight from M (when it leaves A) to m (when it reaches B), with M > m, wouldn't I create kinetic energy for the overall system of 0.5 * (M-m) * v^2 ?
- andrepd 8y agoNo, because its velocity changes too. In relativistic mechanics, the energy momentum relation holds: E^2 = p^2 + m^2, and energy is conserved in a closed system. If on a system with 1 particle the mass changes, the momentum must change to compensate as well.
- blueprint 8y agoBut can such a topic as energy actually mean anything real without it implying the eventual existence of mass..? :)
- im3w1l 8y agoIn a closed system all three quantities would be preserved. According to relativity, invariant mass is a property of a system of particles. You can not find it just by taking all the particles and adding their mass up. A single photon has zero mass, but a system of two photons does have mass (except in the case where they are heading in the exact same direction) and if they do collide mass is preserved.
- lilgreenland 8y agoMass is a type of energy. This means that inertia is dependent on energy not mass (I think). Converting some mass to energy would still require the same force to accelerate.
- phkahler 8y agoFrom a momentum point of view, photons behave as particles with their E=MC^2 mass and velocity C. If you bounce a laser off a mirror, it will exert a pressure which is equal to what you'd get from a (mass equivalent) stream of particles bouncing off it even though photons don't have mass.