Unit 02 · Dynamics & Newton's Laws
Now you ask what causes motion to change. This unit is built on Newton's three laws and the discipline of the free-body diagram: every force named, none invented. You resolve forces into components, solve for acceleration on flat ground and on inclines, and treat friction as a force that depends on the normal force, not on speed. Mastery means you can look at any situation, draw the forces that are actually there, and predict what happens next.
| Criterion | Not yet | Approaching | Mastered |
|---|---|---|---|
| Newton's three laws | Recites the laws but applies them to the wrong situations. | States each law but confuses inertia with the second law. | Applies the right law to each situation and explains why an object at constant velocity has zero net force. |
| Free-body diagrams | Adds phantom forces (like "the force of motion") or omits real ones. | Draws most forces but misplaces the normal force on an incline. | Draws complete, correct free-body diagrams for any object, including inclines and connected systems. |
| Net force & acceleration (F = ma) | Adds force magnitudes without regard to direction. | Finds net force on flat ground but stalls on inclined-plane components. | Resolves forces into components and solves for acceleration on flat and inclined surfaces. |
| Friction | Thinks friction depends on surface area or speed. | Uses the friction equation but confuses static and kinetic. | Distinguishes static from kinetic friction and relates each correctly to the normal force. |
| Lab technique (force measurement) | Misreads the spring scale or ignores the string's mass assumptions. | Takes readings but does not check the system against prediction. | Uses an Atwood machine or force table to measure forces cleanly and compares result to prediction 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. |
“On the incline there’s gravity straight down, the normal force perpendicular to the surface, and friction up the slope. I rotate my axes to the ramp, split gravity into components, and only the along-ramp part drives the acceleration. No 'force of motion' — that’s not a real force.”
“There’s the push forward and gravity down, and friction is bigger because the block is wide.”
You demonstrate this unit through force-measurement labs plus short oral checks where you draw and defend a free-body diagram aloud — not a multiple-choice test. A criterion counts as mastered only when you can both take clean force 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.