4 ms·

In relativity, energy and momentum are understood as equals, distinguished by direction. Energy is "momentum through time" while momentum is "energy through spa

In relativity, energy and momentum are understood as equals, distinguished by direction. Energy is "momentum through time" while momentum is "energy through space." There's not really a good word for it (but see "momenergy.") We can imagine systems where energy is not conserved. Physicists work with these systems all the time. Electrical engineers consider the power coming from the outlet, not the entire (solar-sized) system which conserved energy. In our EE's system, E is not conserved but F=ma still holds. So F=ma is true even if energy is not conserved.

roenxi 7y ago
> In our EE's system, E is not conserved but F=ma still holds. So F=ma is true even if energy is not conserved. Well; no. Energy is conserved. Just because the electrical engineer is ignoring that fact doesn't stop it being important. Same with the physicists. F = ma is a very convenient equation. But energy conservation is a simpler, more fundamental concept and forces are a mathematical artefact of that which happen to be easy to work with.