Braking distance: dry road, wet road and ice
Three identical cars with locked wheels slide at the same speed on dry asphalt, wet asphalt and ice. The stopping distance on ice is eight times longer.
Drag to orbit the scene, scroll to zoom. Press “Run”.
What the experiment shows
Friction between the tyres and the road stops the car. It is large on a dry road, smaller on a wet one and almost gone on ice. The weaker it is, the farther the car travels before it stops.
How to run it
- Press “Run”: all three cars start braking at 5 m/s.
- Measure each car’s stopping distance on the marks.
- Divide the distance on ice by the distance on dry asphalt: how many times longer is it?
Questions to discuss
- How does the stopping distance change if the speed doubles?
- Does the stopping distance depend on the car’s mass?
The science
Friction F = μ·m·g decelerates the car at a = μ·g. The distance to a stop is s = v² / (2·μ·g). At v = 5 m/s: μ = 0.8 gives 1.6 m, μ = 0.4 gives 3.2 m, μ = 0.1 gives 12.7 m. The mass cancels while the speed enters squared: twice as fast, four times the distance.
Try it at home
Slide a block with the same push over linoleum and a carpet and compare where it goes farther. Then put wet foil under it.
What to change in the editor
- Double the cars’ speed (vx = 10) and compare the distances.
- Make one car three times heavier.