Explicit physics instruction
Density is mass per volume, ρ=m/V. Floating depends on average density and displaced fluid, not simply on total mass.
Fluid pressure increases with depth because deeper points support more fluid above. Pressure acts in all directions within a static fluid.
Archimedes’ principle states that buoyant force equals the weight of displaced fluid. Floating equilibrium occurs when buoyant force balances weight.
Core relations: ρ=m/V; F_b=weight of displaced fluid.
Worked example
A 600 g sample occupying 300 cm³ has density 2.0 g/cm³.
Guided question
Calculate density for 500 g occupying 250 cm³.
Independent work
- Solve three density/buoyancy problems.
- Draw one fluid force diagram.
- State one assumption or uncertainty.
Misconception check
A heavier object can float if its average density is low enough and it displaces sufficient fluid.
Formative check
What sets buoyant-force magnitude in Archimedes’ model?
Reveal response
The weight of the displaced fluid.
Mentor evidence conference
Ask Archaemenes to audit density units, displacement reasoning, and force balance.
Teacher guidance
Foundation: Calculate density and identify buoyant direction.
Core: Apply Archimedes’ principle and equilibrium.
Extended: Analyze stability and uncertainty.