The Columbia Encyclopedia, Sixth Edition. Columbia Encyclopedia World Factbook American Heritage Coll.
Motion is caused by an unbalanced force acting on a body.
With the principles of dynamics one can solve problems involving work and energy and explain the pressure and expansion of gases, the motion of planets, and the behavior of flowing liquids and gases. These include fluid mechanics , the study of liquids in motion, and aerodynamics, the study of gases in motion. The applications of liquids both at rest and in motion are studied under hydraulics , a branch of engineering closely related to dynamics. The principles of dynamics may also be combined with the study of other phenomena, as in electrodynamics , the study of charges in motion. The Columbia Encyclopedia, Sixth Edition.