Teach lesson
Buoyancy: density predicts floating
Students use the Buoyancy remote lab to test whether object density, not mass alone, predicts floating and sinking in water.
Learning Outcomes
Calculate density from mass and volume for real lab objects.
Predict floating or sinking by comparing object density with water density.
Use two lab rows to show why mass alone does not decide floating.
Write a claim-evidence-reasoning explanation supported by lab observations.
Student activity preview
Activity Content
Preview only. In a class session, students can fill in responses and submit their work to the teacher.
Start with the model
8 min
Picture two objects in the water: a huge ship loaded with metal and a small pebble you can hold in your hand. The ship can float while the pebble sinks, so "heavy objects sink and light objects float" is not a good rule.
In this lab, you will test a better rule with real objects. Some objects may look like they should behave one way, but the numbers can tell a different story. The useful question is: how much mass is packed into each unit of volume compared with the liquid around it?
An object does not float because it is simply "light." It floats when the same volume of liquid can support it. A useful shortcut is density:
Density comparison
\rho_{\text{object}}=\frac{m}{V}
\qquad
\rho_{\text{object}}<1.00\ \text{g/cm}^3 \Rightarrow \text{usually floats in water}
Density rule for this lesson
The diagram only shows the comparison rule. In the lab you will read mass and volume, calculate density, compare with 1.00 g/cm3, and then observe whether the object actually floats or sinks.
Which comparison should you use first when predicting whether one of these objects floats in water?
Before opening the lab, describe how you will make a density-based prediction for one object. What values will you need, and how will you compare the calculated density with water?
Collect density evidence
25 min
Use one row for one object. Do not mix the mass from one object with the volume or observation from another object.
The lab may show more object cards than this activity uses. Start with the objects named in the table examples.
Open the Buoyancy lab
Open the Buoyancy lab from this activity.
Choose one of the object cards named in this activity.
Record the object name, mass, volume, liquid, and liquid density.
Calculate object density as mass divided by volume.
Predict
float,sink, ornear threshold.Press the down-arrow button to lower the object into the liquid. Watch until the motion settles.
Record the observed state as
floats at the surface,sinks to the bottom, ornear threshold / hard to decide.Repeat until you have at least five complete rows.
Density evidence table
Fill one row per object. Use the values shown by the lab. Object density must be calculated from mass divided by volume. Leave unused rows blank.
| Object | Mass g | Volume cm3 | Calculated density g/cm3 | Liquid density g/cm3 | Prediction | Observation | Evidence note |
|---|---|---|---|---|---|---|---|
Choose one row and enter its calculated density in g/cm3. In the explanation box, show mass divided by volume with units.
Use the evidence
22 min
Look in your table for two objects where mass alone would give a weak prediction, especially if their masses are similar but their volumes, densities, or observed states differ.
Use two rows from your table to show why mass alone is not enough to predict floating. Your answer must mention mass, volume or density, and the observed state.
Optional annotated evidence
Optional: attach one extra piece of evidence, such as an annotated table, a small density-vs-observation graph, or a labelled lab screenshot. Use it only if it helps support your final claim.
Write a claim-evidence-reasoning paragraph: does the Buoyancy lab support the density model for floating and sinking in water? Include at least two rows from your table and one limitation or uncertainty.