Acceleration

The term acceleration, used in physics, is a vector quantity. This means that acceleration contains both a number (its magnitude) and a specific direction. An object is said to be accelerating if its rate of change of velocity is increasing or decreasing over a period of time and/or if its direction of motion is changing. The units for acceleration include a distance unit and two time units. Examples are m/s² and mi/hr/s. Sir Isaac Newton (1642-1727) in his second law of motion defined acceleration as the ratio of an unbalanced force acting on an object to the mass of the object.