**Acceleration**

Acceleration occurs when there is a change in speed – speeding up or slowing down. It is commonly termed acceleration when the speed is increased and deceleration when the speed is decreased. Acceleration can also be described as a change in direction. You may have seen graphs or diagrams illustrating acceleration – velocity-time graphs and ticker-timers:

**Acceleration is a vector** so is often described as being positive in one direction and negative in the other. Acceleration is defined as a change in velocity divided by the time interval. The equation for acceleration is:

**where:**

= the acceleration in m/s^{2}

= the final velocity in m/s

= the initial velocity in m/s

= the time in s

The equation can be rearranged to calculate any of the variables required.

**Example 1:**

What is the acceleration of a vehicle that has an initial speed of 3 m/s and it increases its speed to 11 m/s over a time interval of 4 seconds?

**using:**

= 2 m/s^{2}

**Example 2:**

How long does it take a cyclist to accelerate from rest to 4.5 m/s if they are accelerating at 0.5 m/s?

**using: **

= 9 s