How Would You Define Acceleration? Acceleration is the rate at which velocity changes over time, in terms of speed and direction. A point or object that moves in a straight line is said to be accelerated if it speeds up or slows down. Even if the speed is constant, motion on a circle accelerates because the direction changes all the time. For all other forms of motion, both effects contribute to acceleration.

Because acceleration has both magnitude and direction, it is classified as a vector quantity. Acceleration is defined as the change in velocity vector over a certain time interval divided by that interval. The limit of the ratio of the change in velocity during a given time interval to the time interval as the time interval approaches zero defines instantaneous acceleration (at a specific moment and location). If velocity is reported in metres per second, acceleration will be expressed in metres per second per second.

Acceleration is defined as an increase in an object’s speed or velocity caused by force. For example, if a pen is dropped, it will fall to the ground due to gravity. As it falls, it moves at an acceleration due to gravity of 9.8 meters per second per second (32 feet per second per second).

This indicates that after one second, it is moving at a rate of 9.8 meters per second (32 feet per second). After two seconds, it moves twice as fast. If it was dropped from a tremendous height, it would be moving quite quickly when it impacted the ground.

If a car travels at a constant speed of 50 km/h (31 mph), it does not accelerate. It is moving, but its velocity does not change. If it slows, it loses acceleration. This is referred to as deceleration.

Content for this question contributed by Allison Leber, resident of Glenshaw, Green County, Pennsylvania, USA