Float or sink simulator

What this simulator shows

Whether something floats depends on its density, how much mass is packed into each bit of space, compared with the liquid's density. Here density is measured in grams per cubic centimeter (g/cm³). Fresh water is 1.00, the cooking oil is 0.92 and the very salty water is 1.20. Tap an object on the shelf to drop it in; with Predict first switched on, you choose float or sink before it falls. A number line under the tank shows every object's density against the liquid's.

• Less dense than the liquid: it floats. More dense: it sinks.
• A floating object sits lower the closer its density is to the liquid's. Wood (about 0.5) rides high; ice (0.917) is mostly underwater.
• The solid plastic toy (about 1.05) sinks in fresh water but floats in very salty water.
• Steel (7.9) sinks, but a steel boat shape holds lots of air, so its average density is far lower and it floats.

Why predicting first helps

Children come with strong ideas about floating, and the simulator is most useful when those ideas are tested. Predicting before each drop, and then switching liquids with the same objects in the tank, shows that floating is not a property of the object alone. It depends on the object and the liquid together.

Common misconceptions

The classic wrong rule is that heavy things sink and light things float. A huge log floats while a tiny coin sinks, so weight alone can't be the answer; it is the weight for its size that matters. Another is that big things sink. A third is that things with holes or air float because air pushes them up; the boat floats because the air makes its average density low. Children are often surprised that ice floats at all, since most solids sink in their own liquid. Water is unusual: it expands as it freezes.

The densities here are typical values. Real apples, rocks and woods vary, and so do oils.

A 10-minute float or sink activity

• Ask the child to sort the seven objects into float and sink predictions on paper.
• Drop each one into fresh water with Predict first on. Tally the correct predictions.
• Leave everything in the tank and switch to very salty water. Ask what changed and why.
• Try the steel boat, then squash it. Ask: "Is it still the same steel? Why does it sink now?"
• If you can, test a real apple and a real coin in a bowl of water.

Where this fits in school

• US, grade 2: NGSS 2-PS1-1 asks students to classify materials by their observable properties.
• US, grade 5: NGSS 5-PS1-3 asks students to identify materials based on their properties. In middle school, density becomes a key property for identifying substances.
• England, Key Stage 1 and 2: floating and sinking is a popular hands-on investigation when pupils compare materials.
• England, Key Stage 3: pupils study upthrust, floating and sinking.

Learning more

Materials and their properties are part of Eurekami's science skill map. Lessons draw and explain ideas like density step by step, and daily practice includes a few science questions to keep them fresh.