The rate of change of an object's [[velocity]].<ref>Wile, Dr. Jay L. ''Exploring Creation With Physical Science''. Apologia Educational Ministries, Inc. 1999, 2000</ref>. For an object to undergo an acceleration, a [[force]] needs to be exerted on the object. An example is a falling object on [[Earth]], which is subject to a [[gravity|gravitational force]]. The resulting acceleration ''g'' is independent of the mass of the object, and is approximately 9.81 [[meters]] per [[second]] per [[second]] near the Earth's surface<ref>Marcelo Alonso and Edward J. Finn, ''Fundamental University Physics'', Addison-Wesley.</ref>.
Calculation of acceleration is done with the formula <math>F=MA</math>, where F=force and is measured in Newtons, M=mass and is measured in kilograms, and A=accelerationand is measured in meters per second squared. Using the formula we can find that <math>A=\frac{F}{M}</math>.
If an object's acceleration and [[velocity]] have the same sign, the object is gaining [[speed]]. If acceleration and velocity have different signs, the object is losing speed.