Mechanics is the branch of physical science and applied mathematics dealing with the action of forces on bodies. It may be divided into solid mechanics and fluid mechanics. Another classification is as statics – the study of matter at rest – and dynamics – the study of matter in motion. In statics, the on an object are balanced and the object is said to be in equilibrium; static equilibrium may be stable, unstable, or neutral. Dynamics may be further divided into kinematics – the description of motion without regard to cause – and kinetics – the study of motion and force.
Classical dynamics rests primarily on the three laws of motion. Modern physics has shown these laws to be special cases approximating to more general laws. Relativistic mechanics (see relativity theory) deals with the behavior of matter at high speeds, approaching that of light, whereas quantum mechanics deals with the behavior of matter at the level of atoms and molecules.