2.3 - Acceleration
What acceleration is
- Acceleration is how quickly velocity is changing - the change in velocity in a certain amount of time.
- A change in velocity can be a change in speed, a change in direction, or both.
- Acceleration is a vector, so it can be positive or negative.
- Deceleration is negative acceleration: when something slows down, the change in velocity is negative.
The formula for acceleration
Where:
- = Acceleration, in metres per second squared (m/s2)
- = Final velocity, in metres per second (m/s)
- = Initial velocity, in metres per second (m/s)
- = Time taken, in seconds (s)
The change in velocity is the final velocity minus the initial velocity ().
Worked example - Time for a given acceleration
A cyclist accelerates at 1.5 m/s2 from 3.0 m/s to 7.5 m/s. Find the time it takes to do this.
Step 1 - Rearrange the acceleration equation for time
Step 2 - Substitution and calculation
Uniform acceleration and free fall
- Uniform acceleration means a constant acceleration: the velocity changes by the same amount each second.
- The acceleration of an object in free fall near the Earth's surface is uniform. It has the same value as the gravitational field strength, g.
- Near the Earth's surface this value is about 9.8 m/s2 (sometimes rounded to 10 m/s2 or written as 9.81 m/s2).
TermDefinition
AccelerationThe rate of change of velocity, equal to the change in velocity divided by the time taken.
DecelerationNegative acceleration, which happens when an object slows down.
Uniform accelerationA constant acceleration where the velocity changes by the same amount each second.