Slope race: rolling or sliding

What the experiment shows

Three bodies start together from the top of an incline. The sphere and cylinder roll while the cube slides and falls behind due to friction.

How to run it

1. Place the camera to the side and start the race.
2. See who finishes first and who finishes last.
3. In the editor set the cube’s friction to zero — it becomes the fastest.

Questions to discuss

• Why is the wheel one of the greatest inventions?
• Why would a ball not roll at all without friction?

The science

Rolling is sliding plus rotation. Part of the potential energy goes into spinning, so a ball accelerates slower than an ideal frictionless slider. But real sliding comes with friction, and in our model the rollers win.

Try it at home

Roll a ball, a can and an eraser down the same board. Record the finishing order. Then put a cloth on the board and repeat.

What to change in the editor

• Change the slope angle.
• Add a fourth body, like a pyramid.