The tablecloth trick: inertia
A tablecloth is pulled fast and slowly. The first time the cups stay on the table, the second time they ride off and fall.
2D
Age 6+10 min
Momentum & collisionsFriction
Loading simulation…
Press “Run”. Bodies move by the laws of physics: gravity, friction, elasticity.
What the experiment shows
Friction drags the cups along with the cloth, but it needs time to speed them up. A fast pull is over before the cups have moved.
How to run it
- Press “Run”: on the left the cloth flies at 10 m/s, on the right at 1.5 m/s.
- Compare where the cups ended up.
- In the editor find the slowest pull that still leaves the cups on the table.
Questions to discuss
- Is the trick easier with heavy or light dishes?
- What happens if the cloth is rough?
The science
Inertia is a body’s tendency to keep its velocity. Friction F = μ·m·g speeds a cup up at μ·g. During a short pull it gains little speed and barely moves.
Try it at home
Put a card on a glass and a coin on the card. Flick the card away sharply — the coin drops into the glass.
What to change in the editor
- Increase the cups’ friction.
- Add more cups.