Acceleration
The change in velocity divided by the time it takes to make the change. An acceleration can result from a change in speed, a change in direction, or both.
Negative acceleration is called deceleration.

The acceleration of a body can be estimated from it's initial and final velocity and the time taken based on the above equations. Sometimes it is easier to calculate the acceleration based on the initial and final velocity and the distance travelled, e.g. a rough estimate of the deceleration experienced by a door that has been slammed can be calculated based the final velocity which will be zero, the deflection or freeplay when latched and the initial velocity (typically 1.5ms^{1} to 5ms^{1}). This is purely a method of estimating the acceleration, but can be a useful check.
Conversions  
1 gal  =  1 cm s^{2}  1 g  =  9.80665 m s^{2}  
Standard Acceleration due to gravity  =  1 g  1 g  =  32.174 ft s^{2} 
Examples  
Gravity at surface of the Moon  1.62 ms^{2} 
Gravity at surface of the Earth  9.81 ms^{2} 
Gravity at surface of the Sun  2.74x10^{2} ms^{2} 
See also: Angular Acceleration, Displacement, Equations of Motion, G meter, Jerk, Newtons Laws of Motion, Standard Acceleration due to Gravity, Velocity.
Subjects: Classical Mechanics