Unit 07 · Torque & Rotational Motion
Force makes things move; torque makes things turn. This unit builds torque as force times lever arm, uses the balance of torques to solve static-equilibrium problems, and then extends Newton's ideas into rotation with rotational inertia and angular momentum. Mastery means you can find where a beam balances, explain why a figure skater speeds up when she pulls her arms in, and treat rotation as its own consistent parallel to linear motion.
| Criterion | Not yet | Approaching | Mastered |
|---|---|---|---|
| Torque | Thinks only the size of the force matters, not where it acts. | Uses force times distance but ignores the angle or lever arm. | Calculates torque as force times lever arm, accounts for direction, and explains why a longer wrench is easier. |
| Rotational equilibrium | Cannot set up a balance condition. | Balances torques but forgets to also balance forces. | Solves static-equilibrium problems by setting net torque and net force to zero about a chosen pivot. |
| Rotational inertia | Thinks only total mass matters, not its arrangement. | Knows shape matters but cannot compare two objects. | Explains that rotational inertia depends on how mass is distributed and ranks objects that roll or spin accordingly. |
| Angular momentum | Does not recognize a rotational analog to momentum. | Names angular momentum but cannot apply conservation. | Applies conservation of angular momentum to explain spin-up and spin-down when the radius changes. |
| Lab technique (balance / rotational inertia) | Balances by trial and error with no measurement. | Measures distances but does not predict the balance point first. | Uses a meter-stick balance to predict and then verify equilibrium, reporting the result 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. |
“To balance the meter stick I set the torque on the left equal to the torque on the right about the pivot — each is a weight times its distance from the pivot. A small mass far out can balance a big mass close in. And a skater spins faster with her arms in because pulling them in lowers her rotational inertia while angular momentum is conserved.”
“The heavier side always wins, and the distance doesn’t really change anything.”
You demonstrate this unit through balance and rotational-inertia labs plus short oral checks where you reason about torques 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.