This packet is everything a parent or guide needs to assess Unit 03 at home — learning targets, the answers that count as correct, the mastery rubric, calibration examples, and a clipboard score sheet. No multiple-choice test: the student shows mastery by measuring the inward force on a whirling mass and reasoning about what supplies it aloud.
By the end of the Circular Motion & Gravitation unit, a student should be able to:
Six criteria, each judged Not yet / Approaching / Mastered (Page 3).
Whirl a mass, measure the inward force, compare to v²/r.
The student names what supplies the inward force out loud (Page 4).
Radius, period, and measured force kept distinct.
You are making a decision, not adding up points. For each criterion, decide whether the work is Not yet, Approaching, or Mastered — the column language tells you which. A criterion counts as mastered only when the student can both take the data and justify it against the physics. A student carries three tokens per term; one token buys a re-do of one criterion on another day, so a single bad afternoon never sinks the unit.
Accept any answer in the synonyms column — they are pre-approved as equivalent. The third column flags the confusions that look close but are not yet, so you can coach precisely.
| Canonical answer | Accepted synonyms | Common confusion / discriminator |
|---|---|---|
| Circular motion | ||
| Centripetal acceleration | center-seeking acceleration; v²/r | Points toward the center, not along the motion |
| Centripetal force | net inward force | A role filled by a real force, not a new kind of force |
| Period | time per revolution; T | Time per cycle; frequency is its inverse |
| Tangential velocity | speed around the circle | Direction is along the tangent; it constantly changes |
| Gravitation & orbits | ||
| Universal gravitation | Newton's law of gravity | Force falls off as the inverse square of distance |
| Inverse-square law | 1/r² dependence | Double the distance → one quarter the force |
| Mass vs weight | amount of matter vs gravitational force | Mass is constant; weight changes with the field |
| Orbit | continuous free fall | Falling, but moving sideways fast enough to keep missing the ground |
| Criterion | Not yet | Approaching | Mastered |
|---|---|---|---|
| Centripetal acceleration & force | Thinks an object in a circle has no acceleration at constant speed. | Knows there is acceleration but points it the wrong way. | Shows centripetal acceleration points to the center, uses v²/r, and explains why speed can be constant while velocity changes. |
| Source of the centripetal force | Invents a "centrifugal force" pushing outward. | Names a real force but not consistently across situations. | Identifies the actual force supplying the centripetal requirement — tension, friction, gravity, or normal — in each case. |
| Universal gravitation | Confuses mass with weight; ignores distance. | Uses the gravitation equation but mishandles the inverse-square. | Applies the inverse-square law correctly and distinguishes mass from weight in any gravitational field. |
| Orbits & satellites | Treats orbit as unrelated to gravity. | Links gravity to orbit but cannot relate speed, radius, and period. | Derives the relationship among orbital speed, radius, and period and explains why an orbit is continuous free fall. |
| Lab technique (centripetal apparatus) | Swings the mass erratically; takes no repeatable data. | Collects data but does not control the radius or period cleanly. | Uses a conical pendulum or centripetal-force apparatus to measure force versus speed and compares to v²/r 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. |
The split between Approaching and Mastered is cause over label: not just saying “centripetal force,” but naming the real force that supplies it. Ask “what would happen if the string snapped?” — it flies off along the tangent, not outward.
Read these before you grade. They show what Mastered and Not yet actually sound like, plus the edge cases where you should coach rather than decide on the spot.
Student: ______________________________________ Date: _______________ Guide: _________________________
| # | Criterion | Decision | Notes |
|---|---|---|---|
| 1 | Centripetal acceleration & force | NY / Appr / Mast | |
| 2 | Source of the centripetal force | NY / Appr / Mast | |
| 3 | Universal gravitation | NY / Appr / Mast | |
| 4 | Orbits & satellites | NY / Appr / Mast | |
| 5 | Lab technique (centripetal apparatus) | NY / Appr / Mast | |
| 6 | Integration (cross-domain) | NY / Appr / Mast |
☐ No ☐ Yes — for criterion: __________ Tokens remaining: ☐ 3 ☐ 2 ☐ 1 ☐ 0
NY = Not yet · Appr = Approaching · Mast = Mastered · Unsure between two levels? Circle the lower one and note what a re-do would need.