motion, equation of

Mathematical formula that describes the motion of a body relative to a given frame of reference, in terms of the position, velocity, or acceleration of the body.

In classical mechanics, the basic equation of motion is Newton's second law (see Newton's laws of motion), which relates the force on a body to its mass and acceleration. When the force is described in terms of the time interval over which it is applied, the velocity and position of the body can be derived. Other equations of motion include the position-time equation, the velocity-time equation, and the acceleration-time equation of a moving body.

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▪ physics

      mathematical formula that describes the position, velocity, or acceleration of a body relative to a given frame of reference. Newton's second law, which states that the force F acting on a body is equal to the mass m of the body multiplied by the acceleration a of its centre of mass, F = ma, is the basic equation of motion in classical mechanics. If the force acting on a body is known as a function of time, the velocity and position of the body as functions of time can, theoretically, be derived from Newton's equation by a process known as integration. For example, a falling body accelerates at a constant rate, g. Acceleration is the rate of change of velocity with respect to time, so that by integration the velocity v in terms of time t is given by v = gt. Velocity is the time rate of change of position S, and, consequently, integration of the velocity equation yields S = ¹/₂gt².

      If the force acting on a body is specified as a function of position or velocity, the integration of Newton's equation may be more difficult. When a body is constrained to move in a specified manner on a fixed path, it may be possible to derive the position-time equation; from this equation the velocity-time and acceleration-time equations can, theoretically, be obtained by a process known as differentiation.

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