Acceleration

ac·cel·er·a·tion (ăk-sĕlə-rā'shən)

noun 

• The act of accelerating.
• The process of being accelerated.
• Physics The rate of change of velocity with respect to time.

physics.

1. The rate of change of velocity with time, equal to force divided by mass .
2. Any increase in the speed or rate at which a vehicle moves or a process occurs.
3. The ability of a motor vehicle, etc, to accelerate.