Float or sink?

You will guess what six things do in water and test them one at a time. A small object can sink while a larger one floats, so size is not enough to predict.

Science
Starter
About 10 minutes

Grown-up needed: yes for setup, nearby supervision and handling water or small items

What you need

A shallow bowl of water
Six household objects chosen by a grown-up
A towel
Paper and pencil

The rule

Guess before you drop.

How to do it

Ask a grown-up to select intact water-friendly objects without batteries or sharp edges.
Draw two columns labelled guess and result.
Write your prediction for the first object.
Lower it gently into the shallow water.
Record whether it floats or sinks before removing it.
Repeat with each object and compare the two columns.

Why it works

An object in water experiences an upward force related to how much water it displaces. It floats when that force can balance its weight before it goes completely under. An object with lower overall density than water can usually manage that. Shape and trapped air matter, so a hollow object may behave differently from a solid piece of the same material. The useful question is what fills the whole object, rather than whether it merely looks heavy.

Make it harder

Choose two objects made from different materials.
Compare a hollow container with one filled with water.
Explain a surprising result using both material and shape.

Ask Taz

Why does a small metal spoon sink?
Why does air inside a container help it float?
Why can shape change the result for the same material?

Ask Taz

For grown-ups

Keep the water shallow and stay with the selected objects. This is a prediction exercise rather than a test of who guesses most correctly. Ask your child to explain one changed belief. Ask at dinner: “Which object made you rethink your rule about what floats, and what was inside it?”

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

Can we use what we already have?

Start with the listed household materials. Keep the basic setup small and ask a grown-up to choose suitable items before beginning. The stated time is an estimate, so let the observation decide whether you need longer.

What should we record?

Note the prediction, the result and the one thing you changed. Keeping those separate helps a family discuss what happened without turning an activity into a competition.

Must the result be shared online?

No. A conversation at home is enough. If you choose to share, keep identifying details out and follow the grown-up permission 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