Two moving cars – distance–time graph (s–t)
Integrated ScienceForces & MotionAges 12–13
Use it with your class: students open it from a link or a QR code, with no account needed.
Next in Forces & Motion
Car A and car B move along a straight road at different speeds, with car B given a head start. Press Run and the s–t graph for both cars is plotted in real time; the slope of each line is the speed, shown as a Δs/Δt triangle. Students can drag car B to change its starting position, drag along the graph to scrub through time, and read off the exact moment and position where the two cars meet, where the lines cross.
Lesson: Speed of motion; Distance–time graphs
What it shows
For an object moving at constant speed in a straight line, distance increases by equal amounts in equal times, so its distance–time graph is a straight line whose gradient is the speed, v = Δs/Δt. Two cars share one road here: car A starts from zero and car B has a head start. Both graphs are drawn as the cars move, a stationary car gives a horizontal line, and the crossing point of the lines gives the time and position at which car A catches car B.
How to use
Press Run and watch both lines being drawn while the cars move along the road above. Switch on Show Δs/Δt slope triangle and work out each speed from the graph. Drag car B on the road to change its head start, then drag across the graph to scrub to the crossing point and read the meeting time. Set Speed of car B to 0 to model a stationary car, or make B faster than A so the lines never cross.
Parameters you can change
- Speed of car A 1–20 m/s
- Speed of car B 0–20 m/s
- Car B's head start ahead of A 0–100 m
- Track length 50–300 m
- Show Δs/Δt slope triangle
Questions to explore
- Car A moves at 8 m/s and car B at 4 m/s with a 20 m head start. When does A catch B?
- What does a horizontal line on a distance–time graph tell you about an object's motion?
- How can you tell which car is faster just by looking at the two lines?
