Full context:   In physics, the motion of massive bodies is described through two related sets of laws of mechanics. Classical mechanics for super atomic (larger than an atom) objects (such as cars, projectiles, planets, cells, and humans) and quantum mechanics for atomic and sub-atomic objects (such as helium, protons, and electrons). Historically, Newton and Euler formulated three laws of classical mechanics: If the resultant force F → acting on a body or an object is not equal to zero, the body will have an acceleration a that is in the same direction as the resultant force.