Teach lesson
Buoyancy: changing the liquid
Students compare curated Buoyancy lab recordings in water, oil, and sugar water to see how liquid density changes the float/sink threshold.
Learning Outcomes
Compare object density with the density of different liquids.
Explain why the same kind of object can behave differently in oil, water, and sugar water.
Use borderline cases carefully instead of forcing every result into a simple rule.
Write a short transfer claim about how liquid density changes buoyancy.
Student activity preview
Activity Content
Preview only. In a class session, students can fill in responses and submit their work to the teacher.
The liquid is part of the comparison
10 min
People float more easily in very salty water than in fresh water because the liquid itself is part of the buoyancy comparison. A denser liquid can support objects that would sink in a less dense one.
In the first buoyancy model, you compared object density with water density. This lesson changes the liquid. The lab does not let you pour a new liquid into the same trial. Instead, it gives separate recorded experiments with different object-liquid combinations.
Liquid-density threshold
The diagram marks the density of each liquid. For each lab row, compare your calculated object density with the liquid marker for that row: lower usually predicts floating, higher predicts sinking, and very close values need careful observation.
Which comparison predicts floating in this lesson?
Before collecting data, write the comparison plan for one object-liquid row. Which two density values will you need, and how will you decide whether the object should float, sink, or be near the boundary?
Compare recorded liquid cases
25 min
Each row is a different recorded object-liquid case. Keep the liquid name in the row; otherwise the evidence becomes misleading.
The lab may show more object cards than this activity uses. Focus on the object-liquid cases named in your table rows.
Open the Buoyancy lab
Open the Buoyancy lab from this activity.
For each object card you use, use the mass and volume shown by the lab to calculate object density.
In the table, record object name, liquid, object density, liquid density, prediction, observation, and comparison note.
Predict the state by comparing object density with that row's liquid density.
Press the down-arrow button to lower the object into the liquid and record the observed state. Use wording such as
floats,sinks, ornear the boundary / uncertain, and describe what you see.Complete at least four rows.
Changing-liquid evidence table
Complete at least four rows. The liquid column is required because each row may use a different liquid. You may leave one starter row unused.
| Object | Liquid | Object density g/cm3 | Liquid density g/cm3 | Predicted state | Observed state | Comparison note |
|---|---|---|---|---|---|---|
Choose the most useful pair or trio from your table. Explain how changing the liquid changes the prediction or observation, including the object and liquid density values from those rows.
Transfer the model
20 min
You now have rows from different liquids. Decide what changing the liquid does to the float/sink boundary, and use borderline cases carefully.
Which row is closest to the boundary between floating and sinking? Explain how you know, and why that row should be treated carefully.
Write a final claim about how changing the liquid changes floating and sinking. Use at least two rows from your table, and include one sentence about a limitation of these recorded comparisons.