A plastic cup is floated in the bath and objects are added one at a time, counted aloud together. When the cup sinks, it is emptied and floated again — the aim is to beat the previous count. The reset happens automatically each time. Numbers earned with a physical result carry a different weight than numbers written on a page.
What you need
- plastic cup or yoghurt pot
- small objects (coins, pebbles, bottle caps)
How to do it
- 1How many things can we load before the cup sinks?
- 2Add objects one at a time. Count each one aloud together.
- 3When it sinks, note the number. Empty it and float it again.
- 4Can we load more by placing them differently? Try centre versus edges.
Variations
- Korb-Tür: If they won't add objects — just watch the cup and count aloud. They can push things if they want, or just watch.
- Ausstieg: One final load. Then let the cup sink completely. 'Full sinking.' Done.
💡 Parent tip
Let the child place each object. The act of lowering something carefully into the cup and watching the waterline rise is where the understanding forms. Doing it for them removes the information.
What your child develops
- Buoyancy and load — how weight is distributed affects stability, not just total weight
- Counting with consequence — each number corresponds to a physical change rather than an abstract quantity
- Iterative improvement — trying to beat the previous count is self-motivated engineering
Safety notes
- Keep small objects away from very young children who may put them in their mouths. Never leave children unattended in the bath.
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