When a particle (or any objects) accelerates when acted upon by fundamental forces, what is happening to the amount of energy in that particle? A large example would be an asteroid in space caught by earth's gravity and accelerates toward earth as a result. The fundamental forces here can be electromagnetism, gravity, strong force, and weak force. If a particle accelerates because of gravity or electromagnetism, does that mean it is gaining energy? How does that make sense with the conservation of energy (first law of thermodynamic)? Potential energy is defined as the energy that an object has due to its position in a force field, but where does that potential energy, whether it be gravitational or electric, come from in the first place? I have heard of gravitational energy being negative energy, but what does that mean exactly?