Foil boat. How many coins?

You will shape a foil boat and count its coins before water enters. Foil can float in one shape and sink in another, so weight alone does not settle the challenge.

Build
Explorer
About 15 minutes

Grown-up needed: yes for setup, nearby supervision and clearing spills or loose pieces

What you need

One square of kitchen foil
A shallow bowl of water
Coins handled with a grown-up
A towel

The rule

One square of foil. No extras.

How to do it

Ask a grown-up to place the shallow bowl on a clear table.
Shape the foil into a broad base with raised sides.
Float the empty boat and predict its coin count.
Add one coin at a time near the middle.
Spread the next coins evenly across the base.
Stop at the first water entry and record the previous count.

Why it works

Water pushes upwards on the boat according to the weight of water the boat displaces. A floating boat must displace enough water to balance its own weight and the coins. A wide shape can leave room to displace more water before the rim goes under. Uneven loading can tip one side down early, even when the boat has spare room elsewhere. Once water enters, the added weight makes sinking more likely.

Make it harder

Make the sides lower.
Compare a narrow base with a broad one.
Carry the same coins in a smaller footprint without adding foil.

Ask Taz

Why does foil float as a boat but sink as a tight ball?
Why does piling coins on one side tip it?
Why does water entering make the boat sink?

Ask Taz

For grown-ups

A grown-up should stay with the water and coins, dry spills and keep small coins away from younger children. Compare shape and coin placement separately so the result is easier to interpret. Ask at dinner: “Did your boat run out of room to push water aside, or did one side tip first?”

Taz is an AI and can be wrong, so stay close by. Read how safety works on Taz.

Show us yours

Film your hands and what you made, not your face or name. Ask a grown-up before posting anywhere else.

Questions parents ask

Do we need special equipment?

Use the household items listed above. Begin with a small attempt on a clear surface before trying any harder version. The listed time is an estimate, so leave room to rebuild or repeat without rushing.

What if the first attempt does not work?

Notice where the result first changed. Alter one feature, keep the rest similar and try again. An unsuccessful attempt can still give you a useful question.

Do we have to post the result?

No. You can show it to a grown-up at home. Online sharing is optional and needs the permissions in the privacy line above.

More to try

See all Taz Challenges, or look through the science labs. One place for every why. Ask for early access at aitaz.com