## What is Acceleration?

Any variation from moving at a constant speed in a straight line is described as an acceleration.

It is very important to realize that going faster, going slower, and/or changing direction are all different kinds of acceleration (changing velocities).*Acceleration, a, is defined as the rate of change of velocity with time*.

If the acceleration is constant over time Δt then it can be expressed as: a =Δv/Δt = (v − u)/t

The SI unit of acceleration is meters per second squared, *m/s^2* (the same as the units of velocity/time, m/s/s).

*Acceleration is a vector quantity.*

Acceleration can be:

■ an increase in velocity (positive acceleration)

■ a decrease in velocity (negative acceleration – sometimes called a deceleration)

■ a change of direction.

Now if you like to know in detail about average and instantaneous acceleration, then read the following posts:

– Average Acceleration

– Instantaneous Acceleration

## Velocity-time graph (v-t graph) for an object falling under the effect of gravity, with and without air resistance

Here is a combined diagram showing both the graphs (i.e. v-t graphs with and without air drag)

We have 2 detailed posts that discuss how to draw V-t or velocity-time graphs with and without air-resistance(air-drag). The links are given below:

Motion graphs of vertical fall against air drag

Motion graphs of vertical fall without air resistance (i.e. free-fall)