Sink or float lab
01 // Question
How does an object's density compare to water's density in predicting whether it sinks or floats?
A testable question names one thing you compare (object density vs. water) and one thing you measure (sink or float).
02 // Variables
Independent
Object tested- Wooden block
- Metal spoon
- Plastic bottle cap
- Rubber eraser
- Orange (with peel)
Dependent
Sink or float result- Floats or sinks
- Calculated density (mass ÷ volume), where measurable
03 // Hypothesis
IF an object's density is compared to the density of water (1 g/mL), THEN objects with a density less than 1 g/mL will float and objects with a density greater than 1 g/mL will sink, BECAUSE floating depends on how tightly an object's mass is packed into its volume, not on its total size or weight alone.
04 // Procedure
1. Predict first
Before testing, write down a prediction — float or sink — for each object based on how heavy it feels.
2. Test each object
Gently lower each object into the water and record whether it floats or sinks.
3. Weigh what you can
For regularly shaped objects, measure mass on a scale and volume by water displacement.
4. Calculate density
Divide mass by volume for each measurable object to find its density in g/mL.
5. Compare to predictions
Compare each object's actual result and calculated density against your original prediction.
05 // Data table
| Object | Prediction | Actual result | Density (g/mL), if measured |
|---|---|---|---|
| Wooden block | ____ | ____ | ____ |
| Metal spoon | ____ | ____ | ____ |
| Plastic bottle cap | ____ | ____ | ____ |
| Rubber eraser | ____ | ____ | ____ |
| Orange (with peel) | ____ | ____ | ____ |
Formula Density = mass ÷ volume; density less than 1 g/mL floats in water, greater than 1 g/mL sinks
06 // What to expect
Objects less dense than water — like the wooden block, the bottle cap and often the whole orange (thanks to air pockets in its peel) — float, while denser objects like the metal spoon sink, regardless of how big or small each object is.
Predictions based only on 'heaviness' are often wrong — a large wooden block can weigh more than a small metal spoon and still float, because floating depends on density (mass packed into volume), not total mass alone.
07 // Lab notes
- Lower objects into the water gently rather than dropping them, so splashes don't affect nearby results.
- An orange with its peel on often floats, but the same orange peeled usually sinks — a good follow-up test showing how much the peel's trapped air matters.
- Dry each object between tests if reusing the same water, since a wet object can behave slightly differently than a dry one on re-entry.
08 // Remember
Heavy things don't automatically sink. Density decides — how much mass is packed into the space an object takes up.
09 // Questions people ask
Why does a heavy object like a log float while a small object like a marble sinks?
Floating depends on density — how much mass is packed into a given volume — not on total weight alone. A log is made of wood, which is less dense than water even though the whole log weighs a lot. A marble is made of dense glass or steel, so even though it's small and light, its material is packed more tightly than water.
Why does an orange float with its peel on but sink without it?
An orange peel is full of tiny air pockets. Those air pockets lower the orange's overall density enough to bring it below the density of water, so it floats. Peeled, the orange loses that trapped air and becomes dense enough to sink.
What is the density of water, and why does it matter for sinking and floating?
Water has a density of about 1 gram per milliliter. Any object with a density lower than that floats, because it's less tightly packed with mass than the water it displaces, and any object with a density higher than that sinks, because it's more tightly packed than the same volume of water.