Average speed vs. average velocity
Calculate both averages using the full elapsed time.
Walk out and return to the same door.
Need an earlier step? Start with position, distance & displacement →
Walk 6 m from a door, then walk 6 m back. The whole trip takes 6 seconds. You definitely moved—but you ended where you started.
Words and symbols you will use
- Average
- A description of an entire time interval, not necessarily each instant.
- Elapsed time Δt
- Finish time minus start time; include any pauses during the trip.
- “Per second”
- Divide a total by the number of seconds to find its average rate.
Read the picture, one step at a time.
- Count the route: 6 m out plus 6 m back gives 12 m.
- Compare endpoints: finish minus start is 0 m.
- Use the same 6 s for both averages: 12 ÷ 6 = 2 m/s, but 0 ÷ 6 = 0 m/s.
| Compare | What it means | What follows |
|---|---|---|
| Average speed | Total distance ÷ elapsed time | 12 m ÷ 6 s = 2 m/s |
| Average velocity | Displacement ÷ elapsed time | 0 m ÷ 6 s = 0 m/s |
The idea to keep: Zero average velocity does not mean “never moved.” It means the net position change during the chosen interval was zero.
How can average velocity be zero when you were moving?
Average velocity uses net displacement. Returning to your starting point makes it zero even when your average speed is positive.
Both averages use the total elapsed time, including pauses. Average speed answers how much path was covered per second. Average velocity answers how much net position change occurred per second in a specified direction.
Do not usually average two speed values by adding and dividing by two. That shortcut works when the two intervals last equally long. For equal distances traveled at different speeds, the slower segment takes longer and affects the overall result more.
A reliable approach
- Find total distance and net displacement separately.
- Find the elapsed time from the beginning to the end, including rest.
- Divide each quantity by the same total time and include units.
Work through one example.
A runner travels 60 m east in 10 s and 60 m west in 20 s. Find the two averages.
Follow the worked solution
- Distance = 120 m; displacement = 0 m; elapsed time = 30 s.
- Average speed = 120/30 = 4 m/s.
- Average velocity = 0/30 = 0 m/s. The simple mean of 6 and 3 m/s would incorrectly give 4.5 m/s.
The magnitude of average velocity is not generally equal to average speed.
Explain it without notes: Explain why an out-and-back trip can have a positive average speed and zero average velocity.
Try explaining it now.
A runner’s entire out-and-back route is 100 m and takes 30 s. Is average speed zero?
Compare with an explanation
No. Average speed is 100/30 ≈ 3.33 m/s. Average velocity is zero because displacement is zero.
Another explanation, if you need oneOptional external lesson · Flipping Physics
Displacement, velocity and acceleration
This lesson is complete without a video. For another teacher’s explanation, open the original resource below. Pause after a diagram and explain the idea in your own words.
Suggested section 3:12–8:06. Video by Flipping Physics / Jonathan Thomas-Palmer. Refresh Kid is not affiliated with or endorsed by Flipping Physics. These links open another website. Some videos use g = 9.81 m/s²; our examples state g = 10 m/s². Follow the value given in each problem.
After watching: Explain why an out-and-back trip can have a positive average speed and zero average velocity.
Make a prediction. Test it.
Use the route controls to make the final position equal the starting position. Increase the elapsed time: explain which average remains zero and which decreases.
Motion graphs · same clock, different quantities
Try two questions.
Two original Refresh Kid questions. Choose an answer, explain it to yourself, then check the reasoning. These are not released AP exam questions.
Show your reasoning.
Original mini-FRQ · 4 points · Self-checkA student walks 30 m east in 10 s, waits 5 s, then walks 10 m west in 5 s.
- Find elapsed time.
- Calculate average speed.
- Calculate average velocity with east positive.
- Explain why these are different.
Your response stays on this page and is not submitted or automatically graded. Copy it before leaving.
Compare with the worked solution & scoring guide
- 1 point: Total time = 20 s.
- 1 point: Distance = 40 m; average speed = 2 m/s.
- 1 point: Displacement = +20 m; average velocity = +1 m/s.
- 1 point: The westward segment increases distance but reduces net displacement.
Accept an equivalent correct method. This is a Refresh Kid teaching rubric, not an official AP scoring guideline.
Retrieve it before you reveal it.
RECALL 1Do pauses count in elapsed time?
Yes, if they occur within the specified interval.
RECALL 2When do average speed and |average velocity| agree in 1D?
When there is no reversal of direction over the interval.
RECALL 3Why can simple averaging of speeds fail?
The speeds may persist for different amounts of time.
Come back tomorrow: answer these with the cards closed. Try again a week later, especially the ones you missed.
Keep the key ideas handy.
Average speed vs. average velocity
Core idea: Average velocity uses net displacement. Returning to your starting point makes it zero even when your average speed is positive.
- v_avg = Δx/Δt
- Average speed = total distance/Δt
Avoid this: The magnitude of average velocity is not generally equal to average speed.
Remember why: Zero average velocity does not mean “never moved.” It means the net position change during the chosen interval was zero.
Include pauses in the interval and use the same total time for both averages.
Explain, don’t just substituteExplain why an out-and-back trip can have a positive average speed and zero average velocity.
Refresh Kid · AP Physics 1 · Unit 1 · 1.2.B · Check units, direction and model assumptions.
Connect to released AP practice.
2026 · Question 1 · Version J
Use Part A(i) for component velocity graphs and Part A(ii) for a kinematics derivation. The remaining parts use fluid concepts from Unit 8; they are not Unit 1-only practice.
This is a Unit 1 synthesis task to revisit after learning projectile motion. Historical papers may use different timing or course coverage. Official questions remain on College Board’s site; our questions below are original practice.
Browse released years and scoring information ↗Framework alignment: College Board CED, Topic 1.2. Current exam corrections. Checked September 16, 2026. These explanations and practice items are independently authored by Refresh Kid. The simulation is a mathematical model, not experimental data.
About the videos and learning approach
Optional videos are linked to the publisher’s website and YouTube channel with credit. No external video player is loaded on this lesson page. The written lessons, simulations and practice here are independently authored by Refresh Kid.
We combine worked examples, visual models, explanation and recall practice. See the Institute of Education Sciences study guide ↗ for the underlying learning recommendations.
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