### What is Acceleration?

Prior to discussing about how to calculate average acceleration, let’s define it. Most people tend to relate high speed to acceleration and that’s clearly not true as acceleration only exists when there is change in velocity.

For instance, if an aeroplane is traveling in a straight line at a constant speed of 1,000 K mph and a car is also traveling in a straight line at the speed of 80 K mph, there is no acceleration here as the two are neither increasing or decreasing speed or changing direction.

Both acceleration and speed or velocity are vector quantities.

Since velocity is the rate of change in displacement, hence, acceleration is the rate of change of the velocity of an object with respect to time.

We say a body is in a positive acceleration if there is an increase in velocity with time while a negative acceleration means that the speed reduces with time. Sometimes we say a body is in zero acceleration to mean that its it at rest.

### What is Average Acceleration?

Average Velocity is the rate of change in velocity over a time period.

Therefore to calculate Average Velocity we divide the change in velocity by the change in time.

The SI unit used to measure acceleration is m/s².

**Formula to calculate average acceleration.**

Change in velocity is the difference between the initial velocity and the final velocity.

Change in time mostly means, the difference in time from time 0 to the final time recorded.

**Example 1:**

Loise just bought a new car which goes from 0 to 50 m/s in just 5 seconds. Calculate the acceleration of the car.

Therefore, the average acceleration of the car is 10m/s².

**Example 2:**

A car is driving down the road at 20 meters per second when the driver notices a stop sign up ahead. The driver applies the brakes and comes to a stop in 5 seconds. What was the average acceleration when the brakes were applied.

In this word problem we are dealing with negative acceleration as the car’s initial velocity was 20m/s before it stopped.

Therefore, the average acceleration or rather, the average deceleration of the car is -4m/s².