In physics, work results when a force acts on an object that moves, provided the force isn’t at right angles to the object’s motion. Energy is a central concept in physics; kinetic energy and potential energy are among the types of energy used in physics. One of the most important principles in physics is conservation of energy, which in this context states that as long as the only forces acting are conservative, then an object’s total energy—the sum of its kinetic and potential energy—is unchanged.