Speed is how fast something moves, while velocity is the speed of an object in a given direction. Free GCSE AQA Physics notes and 13 questions answered.
Updated 20 Mar 2026 · Revise Right Team
Distance, Displacement and Speed (Part 3/3) is part of Forces and motion in GCSE AQA Higher Physics.
4 min
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39
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GCSE AQA Higher
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What this lesson covers
Speed is how fast something moves, while velocity is the speed of an object in a given direction. Free GCSE AQA Physics notes and 13 questions answered.
Calculate average speed for journeys involving non-uniform motion using total distance and total time
Explain the difference between speed and velocity, identifying velocity as a vector quantity
Compare scalar and vector quantities, applying this distinction to distance, displacement, speed and velocity
Apply speed and velocity calculations to real-world motion scenarios
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Use this lesson to stay inside Forces and motion while connecting the detail back to the wider Forces topic.
Forces
Forces and motion
GCSE AQA Higher Physics
Revision notes
Read the core explanations from Distance, Displacement and Speed (Part 3/3) before testing yourself from memory.
1. Average Speed for Non-Uniform Motion
Most real journeys don't happen at constant speed. You might walk quickly to the bus stop, wait for the bus, then travel at different speeds depending on traffic. How do we calculate speed for these complex journeys?
The key insight is that average speed uses the total distance and total time for the entire journey. It doesn't matter how the speed varied during different parts - we're finding the single speed that would give the same overall result.
The formula remains the same as before: average speed = total distance ÷ total time. But now we need to add up distances and times from different parts of the journey.
Worked example: Calculating Average Speed for a Multi-Stage Journey
A student walks 200m to school in 4 minutes, stays at school for 6 hours, then walks 200m home in 5 minutes. Calculate their average speed for the whole journey.
Total distance = 200m + 200m = 400m — Add distances from each part of the journey
Total time = 4 min + 360 min + 5 min = 369 min — 6 hours = 360 minutes, add all time periods
369 min × 60 = 22,140 s — Speed formula needs time in seconds for m/s units
Average speed = $\frac{400}{22140} = 0.018$ m/s — This is very slow because most time was spent stationary
Answer: 0.018 m/s (or about 0.02 m/s)
Notice how the long stationary period dramatically reduces the average speed. This shows why average speed for the whole journey can be very different from the speed during the moving parts.
2. Understanding Velocity as Speed with Direction
Speed tells us how fast something moves, but it doesn't tell us which way it's going. When direction matters - and it often does in physics - we use velocity instead.
Velocity has the same units as speed (m/s) but includes directional information. For example, "20 m/s north" or "15 m/s towards the school" are velocities, while "20 m/s" is just speed.
This distinction becomes crucial when objects change direction. A car driving around a roundabout at constant speed is actually changing velocity continuously because its direction keeps changing.
**Trap**: Many students think velocity and speed are the same thing. Actually, velocity includes direction, so an object can have constant speed but changing velocity if it's turning.
3. Scalar vs Vector Quantities
Physics quantities fall into two categories based on whether direction matters. Understanding this distinction helps you choose the right quantity for different situations.
Think of scalars as "how much" and vectors as "how much and which way". When you ask "How far did you travel?", you want distance (scalar). When you ask "Where did you end up?", you want displacement (vector).
Scalar Quantity
Vector Quantity
Distance (how far travelled)
Displacement (change in position)
Speed (how fast)
Velocity (how fast and which way)
Time (duration)
Not applicable
Mass (amount of matter)
Weight (force due to gravity)
The key test is: "If I reverse the direction, does the quantity change?" For vectors, yes - velocity north is different from velocity south. For scalars, no - 50 km distance is the same whether you go north or south.
4. Worked Examples and Applications
Let's apply these concepts to exam-style problems. The key is identifying whether the question asks for a scalar (distance/speed) or vector (displacement/velocity) quantity.
Worked example: Distance vs Displacement Calculation
A hiker walks 3 km east, then 4 km north. Calculate: (a) total distance travelled, (b) displacement from starting point.
Distance = 3 km + 4 km = 7 km — Distance is a scalar quantity – simply add the lengths travelled
Right-angled triangle: 3 km east, 4 km north — Displacement is the straight-line distance from start to finish
Displacement = $\sqrt{3^2 + 4^2} = \sqrt{9 + 16} = \sqrt{25} = 5$ km — The hypotenuse gives the magnitude of displacement
Displacement = 5 km at 53° north of east — Vector quantities need both magnitude and direction
Answer: (a) Distance = 7 km, (b) Displacement = 5 km at 53° north of east
Notice how distance (7 km) is larger than displacement (5 km). This happens whenever the path isn't a straight line - you travel further than your final position change.
For velocity calculations, the same principle applies. Average velocity uses displacement and time, while average speed uses distance and time. This can give very different results for journeys involving direction changes.
5. Exam Technique and Common Mistakes
Exam questions often test whether you understand the difference between scalars and vectors. Read the question carefully to identify which quantity is being asked for.
For average speed calculations with non-uniform motion, always use total distance and total time. Don't try to average the different speeds - this gives the wrong answer unless the time periods are equal.
When stating velocity, always include direction. "15 m/s" is incomplete - you need "15 m/s north" or "15 m/s towards the school". Direction can be given as compass directions, angles, or descriptions like "towards" or "away from".
Remember that displacement can be zero even when distance is large (like completing a lap of a track), and average velocity can be zero even when average speed is not. This often appears in exam questions to test your understanding.
Sources and content standards
Published by Revise Right. Use the official specification reference to check the requirements for your course. Content updated: 2026-03-20.
Velocity is the speed of an object in a given direction, measured in metres per second (m/s) in a specified direction. A car driving round a roundabout at constant speed is continuously changing velocity because its direction keeps changing.
How do you calculate average speed?
Average speed is total distance travelled divided by total time taken. A student who walks 200m to school in 4 minutes, stays 6 hours and walks 200m home in 5 minutes covers 400m in 22,140 s, an average speed of about 0.018 m/s.
What is the difference between speed and velocity?
Speed is how fast something moves, while velocity is the speed of an object in a given direction. Both are measured in m/s, but '20 m/s north' is a velocity and '20 m/s' is just speed, so speed is a scalar and velocity is a vector.
Is time a scalar or a vector?
Time is a scalar quantity, because a duration has magnitude only and no direction. Distance, speed and mass are also scalars, while displacement, velocity and weight are vectors.
What is the difference between average speed and average velocity?
Average speed uses total distance and time, while average velocity uses displacement and time. They can give very different results for journeys involving direction changes, such as a lap of a track.
Can displacement be zero when distance is not?
Displacement can be zero even when distance is large, for example after completing a lap of a track, because the finish is back at the start. In the same way, average velocity can be zero even when average speed is not.
Why shouldn't you average the speeds of a journey?
For non-uniform motion, always use total distance and total time rather than averaging the different speeds, which gives the wrong answer unless the time periods are equal. Long stationary periods dramatically reduce the average speed.
What is the average speed for a walk to school and back with a 6-hour stay?
Walking 200 m to school in 4 minutes, staying 6 hours, then walking 200 m home in 5 minutes gives an average speed of 0.018 m/s. Total distance is 400 m and total time is 369 min = 22,140 s, so 400 ÷ 22,140 = 0.018 m/s.
Why does stopping lower the average speed?
A stationary period lowers the average speed because average speed uses the total time for the whole journey, including stationary periods. A long stop adds time but no distance, so the average speed can be very different from the speed while moving.
Does a car on a roundabout change velocity?
A car driving round a roundabout at constant speed is continuously changing velocity, because its direction keeps changing. Velocity includes direction, so constant speed does not mean constant velocity.
What is the distance and displacement of a hiker who walks 3 km east then 4 km north?
A hiker who walks 3 km east then 4 km north travels a distance of 7 km but has a displacement of 5 km at 53° north of east. Distance adds the lengths, while displacement uses Pythagoras' theorem: √(3² + 4²) = 5 km.
How do you state a velocity?
A velocity must include a direction: '15 m/s' is incomplete, while '15 m/s north' or '15 m/s towards the school' is complete. Direction can be given as compass directions, angles, or descriptions like towards or away from.
How do you tell if a quantity is a scalar or a vector?
The test is to ask whether reversing the direction changes the quantity. For vectors it does: velocity north differs from velocity south. For scalars it does not: 50 km distance is the same whether travelled north or south.