(July 23, 2019 at 9:45 am)comet Wrote:(July 23, 2019 at 9:10 am)polymath257 Wrote: No, you misunderstood. Energy is NOT a vector. It is a *component of* a vector. More specifically, it is the time component of the energy-momentum 4-vector. So, in that sense, it has *exactly* the same 'reality as momentum. In other words, it is a *property* of the particles involved.
The PE and KE are not 'components in the vector sense. They are scalars that add up to be the total energy. But, you are working classically, and classical physics is ultimately wrong. When you get to relativistic physics, energy is one component of a four dimensional vector associated with the particle. And, in fact, the energy-momentum vector for a particle always has a (relativistic) length associated with the rest mass of the particle. That is where the equation E^2 = m^2 c^4 +p^2 c^2 comes from (the correct version of E=mc^2 to apply to moving and/or massless particles).
energy is a property that is used. as in "how much energy does it have?" I think I get that.
what type of energy is the time component of energy-momentum 4-vector? what are its parts?
The energy in the energy-momentum 4-vector is the kinetic energy. The other three components of the 4-vector are the usual three components of the momentum.
Potential energy is, ultimately, the kinetic energy of the force carrying particles. So *all* energy is ultimately kinetic energy.
