Everyday material
Bottle cap
A discarded lid offers a round shape, a small container, or a ready-made spacer.
Get to know it
Compare clean plastic caps of different sizes. Their round shape invites wheel experiments, but a cap is not automatically a usable wheel: the axle connection and a centered hole matter. Prefer already prepared caps when an investigation needs holes. A cardboard circle is another wheel idea with different stiffness and rolling behavior.
What happens if…
- Does the rim roll smoothly?
- What happens if the axle is off center?