Speed and Velocity
Speed is how fast; velocity is how fast and in which direction.
About this topic
Speed is the distance travelled per unit time, a scalar: v = d/t. Velocity is displacement per unit time, so it includes direction. A car circling a roundabout at a steady 30 km/h has constant speed but changing velocity, because its direction keeps changing.
Average speed is total distance divided by total time. Units are m/s in SI, and converting is easy: multiply km/h by 1000/3600, or divide by 3.6, to get m/s. So 72 km/h is 20 m/s. Velocity can be positive or negative in one dimension, showing which way the object moves.
Example: a runner covers 100 m in 12.5 s, so her average speed is 8 m/s. If she runs a full lap of a track and ends at the start, her average velocity is zero even though her average speed is not. Speed limits, sports timing and flight planning all rely on these ideas.
Common misconception: speed and velocity are not interchangeable words in physics. Another trap is averaging two speeds for a round trip; if you go somewhere at 40 km/h and return at 60 km/h, the average speed is 48 km/h, not 50, because you spend more time at the slower speed. Always use total distance over total time.
Key ideas
- v = Δx / Δt
- Average vs instantaneous speed
- Units are m/s
Quick check
Use cases: where Speed and Velocity helps
- Homework: review the key idea behind Speed and Velocity before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Speed and Velocity without notes.
- Visual learning: play with the interactive lab to see how Speed and Velocity changes when you adjust its inputs.
- Teaching a friend: explain Speed and Velocity in your own words, then compare your version with the key ideas.
The same laws describe car crashes, sports, satellites and everyday machines.
Frequently asked questions
What is Speed and Velocity?
Speed is how fast; velocity is how fast and in which direction.
What will I learn in Speed and Velocity?
v = Δx / Δt. Average vs instantaneous speed. Units are m/s.
Is Speed and Velocity part of Physics?
Yes. It is one of 150 Physics topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Speed and Velocity lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Speed and Velocity?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.