Article
Speed constant in time. Know any two of v, s, t — the third follows from s = v·t.
Part 1 of Physics without mysteries. Next: accelerated motion.
Uniform motion is the simplest model: speed does not rise or fall. Hold a steady 20 m/s for 90 s and the distance is 1800 m — period. The s(t) graph is a straight line; Galileo already wrote about “equal pace” in the Dialogues (1638).
School tools get mixed up. The v–s–t solver fills any two fields. “Distance only” always computes s = v·t from two inputs. Average speed divides whole distance by whole time including traffic — that is not the speedometer reading.
Practical note: “I was doing ninety” is often instantaneous speed. If there were lights on the route, use average speed. This article and the solver assume v really was constant, or that you knowingly use the ideal school model.
| Situation | Formula | When |
|---|---|---|
| Know v and t | s = v·t | Distance at constant speed |
| Know s and t | v = s/t | Speed (here: constant = average) |
| Know s and v | t = s/v | Travel time with no stops |
| Whole trip with traffic | v̄ = s/t | Average speed — different calculator |
A car travels at constant speed v = 20 m/s for t = 90 s. What distance does it cover?
Steps
Answer: s = 1800 m
At constant v = 25 m/s you need to cover s = 5000 m. How long does it take?
Steps
Answer: t = 200 s
