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 | Developing | Proficient | Mastery |
|---|---|---|---|
| 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) | Makes no supported connection between the source and the science. | Uses the source but needs help connecting evidence, writing, or limitations to the science. | Independently connects History, Reading, and Writing using a cited source, appropriate evidence, a limitation, and a scientific explanation. |
Integration is reported separately and cannot lower the science grade or block a science demonstration pass. Science and practical criteria determine that pass. Use the integration guide's evidence checklist for the separately reported criterion.
“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.