Buoyancy & Floating Worksheet
Goal: Compare an object’s weight with the buoyant force F = ρ_fluid g V_submerged to explain why objects float, sink, or float at a particular depth.
What to do
- Press Reset, then “Wood in water” (500 kg/m³ wood, 2 L, half submerged). Record the buoyant force, weight, net force and floating fraction.
- Press Reset, then “Ice in water”, and record. Repeat with “Steel in water”, pressing Reset first.
- Press Reset, then “Wood in water”. Set the Submerged fraction to 100%, then to 20%, and record both rows.
Record your results
| Setting | Buoyant force | Weight | Net force (up +) | Floating fraction |
|---|---|---|---|---|
| Wood in water, 50% under | ||||
| Ice in water, 92% under | ||||
| Steel in water, fully under | ||||
| Wood pushed fully under | ||||
| Wood only 20% under |
Questions
When the wood is half submerged, the net force is 0. Explain why it floats at exactly that depth.
What happens to the wood if you push it fully under, or hold it only 20% under? Use the net force to explain.
Why does steel sink even though the buoyant force on it is bigger than on the floating wood?
Ice floats with 92% of its volume under water. Use the densities to explain the “tip of the iceberg”.
Predict, then test: in seawater (1025 kg/m³), will ice float higher or lower than in fresh water?
Challenge: a 500 kg/m³ object floats in a fluid of 1250 kg/m³. What fraction of it will be submerged?
Free from The Physics Lab · thephysicslab.org · MS-PS2-2: Investigate how the change in an object’s motion depends on the sum of the forces on it and its mass.