Unit 08 · Fluids & Pressure
The year closes by applying forces and energy to fluids — liquids and gases that flow and push. This unit defines density and pressure, shows how pressure grows with depth, and uses Archimedes' principle to predict what floats and what sinks. It finishes with Pascal's principle and the ideas behind fluid flow. Mastery means you can predict whether an object floats before you drop it in, and explain why from the fluid it displaces.
| Criterion | Not yet | Approaching | Mastered |
|---|---|---|---|
| Density & pressure | Confuses mass with density or force with pressure. | Computes each but not how pressure changes with depth. | Relates density and pressure correctly and explains why pressure increases with depth in a fluid. |
| Buoyancy & Archimedes' principle | Thinks heavy things always sink. | States Archimedes' principle but cannot apply it to predict floating. | Predicts float or sink from the weight of displaced fluid and defends the reasoning quantitatively. |
| Pascal's principle | Does not see how pressure transmits through a fluid. | Knows a hydraulic lift multiplies force but not why. | Explains Pascal's principle and how a hydraulic system trades distance for force at equal pressure. |
| Fluid flow | Ignores that speed and area are related in flow. | Recalls that narrowing speeds flow but not the pressure consequence. | Applies continuity and the qualitative Bernoulli relationship to connect speed, area, and pressure in a moving fluid. |
| Lab technique (buoyancy measurement) | Estimates buoyancy by eye with no measurement. | Weighs an object in and out of water but does not compare to displaced volume. | Measures the buoyant force and the displaced fluid and verifies Archimedes' principle with uncertainty. |
| Integration (cross-domain) | Treats the science as isolated facts; makes no cross-domain connection. | Names a link to history, reading, or writing but cannot defend why it matters. | Connects the unit to its anchor across History · Reading · Writing (plus chosen electives) and defends why the connection matters. |
“It floats if the water it pushes aside weighs more than the object does. A steel hull floats because its shape displaces a huge volume of water — the average density is low even though steel is dense. I can measure the buoyant force as the weight lost when I submerge it, and it matches the displaced water.”
“Metal always sinks and light stuff always floats, and pressure is the same everywhere in the tank.”
You demonstrate this unit through buoyancy labs plus short oral checks where you predict floating and explain it aloud — not a multiple-choice test. A criterion counts as mastered only when you can both take clean data and justify the physics behind it. Mastery is demonstrated, not awarded.
A 5-page clipboard packet — unit overview, key terms, the mastery rubric, anchor examples, and a score sheet you can print and grade against.