Make a prediction
Compare an object's mass with the amount of water its full volume can displace.
Sink or Float
Drop objects into water and explore how their mass and volume affect floating.
Grades 3–5 · Physics
Your goal
Make an object float at the water surface, then drop it.
Reduced motion is on. The controls still update the scene.
Ready to drop. Object density is 1.50 g/cm³ and water density is 1.00 g/cm³.
g
cm³
g/cm³
The picture shows the final position, not falling speed. A neutral block is placed under water at rest. Blocks keep their volume, water stays level, and surface tension is ignored. The boat preset represents the average density of a sealed object including its air.
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Learn with Sink or Float
Sink or Float lets students investigate buoyancy by comparing an object's mass and volume in a tank of water. Try different objects, adjust their properties, and observe whether they float, sink, or remain suspended. The waterline helps show how much of a floating object is underwater. This elementary science activity connects density with displaced water and encourages children to test the idea that heavier objects always sink, using a simplified model of uniform objects in still water.
What to look for
Change the volume
An object can become easier to float when its volume increases while its mass stays the same.
Notice the waterline
A floating object displaces water with the same mass as the object.
For teachers and curious learners
Explain floating using mass, volume, and displaced water. Ask students to predict what will happen, change one setting, and explain what they observe. Learn gives a starting point. Practice and Challenge offer new goals with the same scene.
Objects are uniform and rigid in still water. The model simplifies fluid motion, surface tension, trapped air, and shape-dependent stability.
Continue with Sink or Float Lab .