Can anyone help me understand this equation: Work = ΔK + ΔU + ΔE (no heat). Where K is kinetic energy, U is potential energy, and E is internal energy. This is for nonconservative forces only right? I'm just confused about what if some potential energy is converted into kinetic energy, wouldn't that mean we are counting this amount of energy twice? Does non conservative forces mean energy leaves the system? Thanks.