Science & Logic Challenges Grades K–2

Sink or Float Predictions

Kids predict, then test, whether everyday objects sink or float — a simple hypothesis-and-test loop that’s real science.

15 min 1+ students

What you need

A clear tub or bucket of water, 8–10 small waterproof objects (a cork, a coin, a plastic block, a small rock)

Fill the tub with a few inches of water somewhere spills are okay, and lay out the objects to test.

Hold up an object and ask the class to predict: sink or float? Have them vote with a thumbs up (float) or thumbs down (sink).
Drop the object in and observe the result together.
Ask why they think it happened that way — introduce the idea that it’s about weight compared to size (density), in kid-friendly terms.
Repeat for each object, and sort them into two piles (sank / floated) at the end to look for patterns.

Let kids sort the objects into predicted piles before testing, then check their whole sorted set at once.
Add a "can you make a sinking object float?" challenge with tinfoil to test boat-shape as a follow-up.