Answer:
Acceleration is defined as the ratio between the change in velocity of an object and the time it takes for the object to change the velocity.
In formula, this is written as:
where
vf is the final velocity
vi is the initial velocity
t is the time it takes for the object to accelerate from u to v
Note that acceleration is a vector, so it can also be caused by a change in the direction of the velocity, not only by a change in its magnitude.