AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
The average acceleration of an object can be calculated using the equation:
Full specification wording
Acceleration: The average acceleration of an object can be calculated using the equation:
Average acceleration measures how quickly velocity changes over a time interval.
Checked against the AQA 8464 specification (opens in a new tab) on .
- Point 1 of 21
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Average acceleration measures how quickly velocity changes over a time interval. You calculate it by finding the change in velocity, Δv, and dividing by the time taken, t. Change in velocity means final velocity minus initial velocity, so direction matters: a car slowing from 20 m/s to 5 m/s has Δv = 5 m/s − 20 m/s = −15 m/s, giving negative acceleration, or deceleration. The standard unit is metres per second squared, m/s², because you divide m/s by s. For example, a cyclist speeding from 4 m/s to 10 m/s in 3 s has Δv = 6 m/s and average acceleration = 6 m/s ÷ 3 s = 2 m/s². This equation gives an average value; if acceleration changes during the interval, it does not describe every instant. Always identify initial and final velocities, subtract carefully, then divide by the time interval.
What earns the marks
- State that acceleration is the rate of change of velocity, so it depends on both the size of the velocity change and the time taken.
- Calculate change in velocity using Δv = final velocity − initial velocity, keeping direction signs consistent.
- Substitute Δv and t into acceleration = Δv ÷ t and evaluate with correct arithmetic.
- Use the unit m/s² and recognise that a negative result indicates deceleration or acceleration opposite to the chosen positive direction.
- Interpret the result as an average acceleration over the stated time interval rather than an instantaneous value.
Common mistakes and how to put them right
Adding initial and final velocities instead of subtracting.
Put it right by using Δv = final velocity − initial velocity.
Dividing time by velocity change.
Put it right by dividing the change in velocity by the time taken.
Ignoring direction signs and treating a slowing object as having positive acceleration.
Put it right by choosing a positive direction and keeping signs throughout.
Exam tips
- Write the equation, then substitute values with units before calculating so arithmetic errors are easier to spot.
- Check that the time interval matches the velocity change; if a graph is given, read velocities at the two stated times.
- Give the unit m/s² with your answer and comment on direction if the value is negative.
Try the lesson
The start of the Acceleration: The average acceleration of an object can be calculated using the equation: lesson, made from checked teaching notes for this specification point.
Have a go first
A speedboat accelerates from 5 m/s to 17 m/s in 4 s. Using a = Δv / t, what is the average acceleration of the boat?
Listen
Average acceleration measures how quickly velocity changes over a time interval. You calculate it by finding the change in velocity, Δv, and dividing by the time taken, t. Change in velocity means final velocity minus initial velocity, so direction matters: a car slowing from 20 m/s to 5 m/s has Δv = 5 m/s − 20 m/s = −15 m/s, giving negative acceleration, or deceleration. The standard unit is metres per second squared, m/s², because you divide m/s by s. For example, a cyclist speeding from 4 m/s to 10 m/s in 3 s has Δv = 6 m/s and average acceleration = 6 m/s ÷ 3 s = 2 m/s². This equation gives an average value; if acceleration changes during the interval, it does not describe every instant. Always identify initial and final velocities, subtract carefully, then divide by the time interval. A strong answer earns marks for these points. State that acceleration is the rate of change of velocity, so it depends on both the size of the velocity change and the time taken. Calculate change in velocity using Δv = final velocity − initial velocity, keeping direction signs consistent. Substitute Δv and t into acceleration = Δv ÷ t and evaluate with correct arithmetic. Use the unit m/s² and recognise that a negative result indicates deceleration or acceleration opposite to the chosen positive direction. A common slip: Adding initial and final velocities instead of subtracting. Instead, using Δv = final velocity − initial velocity. Exam tip: Write the equation, then substitute values with units before calculating so arithmetic errors are easier to spot.
See it
Put it in order
Put these steps in the order they happen.
- 1. acceleration = Δv ÷ t
- 2. Result is an average acceleration
- 3. Unit: m/s²
- 4. Identify initial velocity
- 5. Identify final velocity
- 6. Negative result means deceleration
- 7. Δv = final velocity − initial velocity
- 8. Identify time interval t
Key words
Say what each word means before you turn the card.
Average acceleration
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Change in velocity
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Deceleration
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Metres per second squared
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See every definition
- Average acceleration
- A measure of how quickly velocity changes over a time interval, calculated by finding the change in velocity and dividing by the time taken.
- Change in velocity
- Final velocity minus initial velocity, so direction matters and a slowing object gives a negative value.
- Deceleration
- Negative acceleration, occurring when an object slows down so that its change in velocity is negative.
- Metres per second squared
- The standard unit of acceleration, m/s², because you divide m/s by s.
Label the diagram
Some boxes have lost their names. Pick the right name for each number.
1Box 1
2Box 2
3Box 3
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