AQA · GCSE · Physics
Course version: 8463 · Version from Sept 2016
Acceleration: change in velocity, Δv, in metres per second, m/s
The symbol Δv stands for change in velocity, measured in metres per second (m/s).
Checked against the AQA 8463 specification (opens in a new tab) on .
- Point 12 of 23
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
The symbol Δv stands for change in velocity, measured in metres per second (m/s). The Greek letter Δ means 'change in', so Δv = final velocity − initial velocity. Velocity is a vector: it has both size and direction, so a change in direction at constant speed is also a change in velocity. For example, a car travelling at 20 m/s that slows to 8 m/s has Δv = 8 − 20 = −12 m/s; the negative sign shows the change opposes the original motion. If a runner reverses direction at the same speed, the change in velocity is twice the speed because the sign of the velocity reverses. Always record velocities with their direction signs before subtracting.
What earns the marks
- Define Δv as the change in velocity, calculated as final velocity minus initial velocity.
- State that the unit of Δv is metres per second, m/s, because it is a velocity difference.
- Substitute initial and final velocities with correct signs, including negative values for motion in the opposite direction.
- Explain that a change in direction at constant speed still produces a change in velocity because velocity is a vector.
- Use the value of Δv correctly in the acceleration equation a = Δv ÷ t.
Common mistakes and how to put them right
Treating Δv as the final velocity only.
Put it right: Subtract the initial velocity from the final velocity.
Ignoring direction and using speed instead of velocity.
Put it right: Assign positive and negative signs to opposite directions before subtracting.
Giving the unit of Δv as m/s².
Put it right: Use m/s, since Δv is a difference between two velocities.
Exam tips
- Underline the initial and final velocities in the question and write them with signs before doing any arithmetic.
- If an object reverses direction, show the sign change explicitly in your working to avoid losing a mark.
- Check that your value of Δv has the unit m/s before substituting it into the acceleration equation.
Try the lesson
The start of the Acceleration: change in velocity, Δv, in metres per second, m/s lesson, made from checked teaching notes for this specification point.
Have a go first
A cyclist speeds up from 4 m/s to 10 m/s. What is the change in velocity, Δv, in m/s?
Listen
The symbol Δv stands for change in velocity, measured in metres per second (m/s). The Greek letter Δ means 'change in', so Δv = final velocity − initial velocity. Velocity is a vector: it has both size and direction, so a change in direction at constant speed is also a change in velocity. For example, a car travelling at 20 m/s that slows to 8 m/s has Δv = 8 − 20 = −12 m/s; the negative sign shows the change opposes the original motion. If a runner reverses direction at the same speed, the change in velocity is twice the speed because the sign of the velocity reverses. Always record velocities with their direction signs before subtracting. A strong answer earns marks for these points. Define Δv as the change in velocity, calculated as final velocity minus initial velocity. State that the unit of Δv is metres per second, m/s, because it is a velocity difference. Substitute initial and final velocities with correct signs, including negative values for motion in the opposite direction. Explain that a change in direction at constant speed still produces a change in velocity because velocity is a vector. A common slip: Treating Δv as the final velocity only. Instead, subtract the initial velocity from the final velocity. Exam tip: Underline the initial and final velocities in the question and write them with signs before doing any arithmetic.
See it
Key words
Say what each word means before you turn the card.
Δv
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Velocity
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Change in velocity
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Acceleration equation
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See every definition
- Δv
- The symbol for change in velocity, calculated as final velocity minus initial velocity and measured in metres per second, m/s.
- Velocity
- A vector quantity, meaning it has both size and direction, so a change in direction at constant speed is also a change in velocity.
- Change in velocity
- Found by subtracting the initial velocity from the final velocity, with velocities recorded with their direction signs before subtracting.
- Acceleration equation
- The equation a = Δv ÷ t, in which the value of Δv is used correctly.
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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