If a particle is moving with kinetic energy T(x) in a potential field of energy V(x), why is the total energy E(x) = T(x) - V(x), i.e. why is potential energy negative? The way I have seen it explained is that the potential energy is less than if the particle was an infinite distance from the source of the potential energy (e.g. an electron experiencing an attractive force to its nucleus). This does not make sense to me. If you throw a ball, the total energy of the ball is its kinetic energy plus its potential energy due to gravity.