AQA · GCSE · Physics
Course version: 8463 · Version from Sept 2016
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 8463 specification (opens in a new tab) on .
- Point 9 of 23
- 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. Velocity is a vector: its direction matters as well as its size. To calculate average acceleration, find the change in velocity by subtracting the initial velocity from the final velocity, then divide by the time taken for that change. For example, a cyclist speeds up from 4 m/s to 10 m/s in 3 s: the change in velocity is 10 m/s − 4 m/s = 6 m/s, so the average acceleration is 6 m/s ÷ 3 s = 2 m/s². A negative result means the object is slowing down or accelerating in the opposite direction to its motion. The equation gives an average value; if acceleration varies during the interval, the calculation still describes the overall rate of change of velocity.
What earns the marks
- State that acceleration is the rate of change of velocity, so it depends on both the size and direction of the velocity change.
- Calculate change in velocity as final velocity minus initial velocity, keeping signs to show direction.
- Divide the change in velocity by the time taken to obtain the average acceleration.
- Use the unit m/s² for acceleration and show consistent units for velocity (m/s) and time (s).
- Interpret a negative acceleration as deceleration or acceleration opposite to the direction of motion, depending on the chosen positive direction.
Common mistakes and how to put them right
Adding the initial and final velocities instead of subtracting.
Put it right by calculating final velocity minus initial velocity.
Forgetting to convert time to seconds when it is given in minutes.
Put it right by multiplying minutes by 60 before dividing.
Treating acceleration as a scalar and ignoring direction.
Put it right by defining a positive direction and using signs consistently.
Exam tips
- Write the equation, substitute the values with units, then calculate and give the unit m/s².
- If the object slows down, expect a negative answer and explain it as deceleration or acceleration in the opposite direction.
- Check that the time interval matches the velocity change you are using, especially in multi-stage journey questions.
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
Which equation gives the average acceleration of an object?
Listen
Average acceleration measures how quickly velocity changes over a time interval. Velocity is a vector: its direction matters as well as its size. To calculate average acceleration, find the change in velocity by subtracting the initial velocity from the final velocity, then divide by the time taken for that change. For example, a cyclist speeds up from 4 m/s to 10 m/s in 3 s: the change in velocity is 10 m/s − 4 m/s = 6 m/s, so the average acceleration is 6 m/s ÷ 3 s = 2 m/s². A negative result means the object is slowing down or accelerating in the opposite direction to its motion. The equation gives an average value; if acceleration varies during the interval, the calculation still describes the overall rate of change of velocity. 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 and direction of the velocity change. Calculate change in velocity as final velocity minus initial velocity, keeping signs to show direction. Divide the change in velocity by the time taken to obtain the average acceleration. Use the unit m/s² for acceleration and show consistent units for velocity (m/s) and time (s). A common slip: Adding the initial and final velocities instead of subtracting. Instead, calculating final velocity minus initial velocity. Exam tip: Write the equation, substitute the values with units, then calculate and give the unit m/s².
Key words
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Average acceleration
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Velocity
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Change in velocity
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Negative acceleration
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See every definition
- Average acceleration
- Calculated by dividing the change in velocity by the time taken for that change, giving an average value over the interval.
- Velocity
- A vector quantity, so its direction matters as well as its size.
- Change in velocity
- Found by subtracting the initial velocity from the final velocity, keeping signs to show direction.
- Negative acceleration
- A negative result means the object is slowing down or accelerating in the opposite direction to its motion.
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