A boat downstream and back
A boat covered a given distance downstream in a few hours. Find its speed downstream and on the way back.
2D
Age 10+10 min
Motion problems
Loading simulation…
Press “Run”. Bodies move by the laws of physics: gravity, friction, elasticity.
What the experiment shows
The upper boat goes downstream and reaches the finish in the given time. The lower one returns against the current and shows its speed.
How to run it
- Run the scene: the boats go with and against the current, and each shows its speed.
- Enter your answer in the Task panel and press “Check”.
- Set the current to 0 and compare the speeds: what changed?
Questions to discuss
- Why is the current added downstream and subtracted upstream?
- What happens if the current is faster than the boat's own speed?
The science
Downstream the boat's speed is its own speed plus the current, upstream their difference: v down = v₀ + vc, v up = v₀ − vc. The downstream speed exceeds the upstream speed by 2vc.
Try it at home
Float a paper boat in a stream or in a tub with a hose current and time it over one metre.
What to change in the editor
- In the editor set the current so that the boat upstream stands still.
- Add a second boat with a different speed and make a race.