A motorcyclist and a truck toward each other

What the experiment shows

The truck's speed is not a number but a fraction k of the motorcyclist's. The k slider changes it and the labels above the vehicles update.

How to run it

1. Run the scene and watch the S caption: the distance between them shrinks steadily.
2. Enter your answer in the Task panel and press “Check”.
3. Move the sliders and solve again: the statement updates itself.

Questions to discuss

• Why are the speeds added when moving toward each other?
• How does the meeting time change if the distance doubles?

The science

Every hour the gap shrinks by the sum of the speeds: the closing speed. The meeting time is the distance divided by the closing speed: t = S / (v₁ + v₂).

Try it at home

Mark two points 20 steps apart on the pavement and walk toward each other with a friend, comparing how many steps each took.

What to change in the editor

• Open the example in the editor and swap the participants for other shapes, changing the speed scale.
• Add a “delay” variable and let one leave later to get a catch-up problem.