Work through the list without notes. If you cannot do a statement, follow its link, then come back. Guide = study guide; Practice = practice questions.
Understanding
- I can explain what a rigid system is and why every torque must be measured about a stated axis. (Guide: “Rigid systems and the axis of rotation”; Practice Q6)
- I can explain why only the component of a force perpendicular to r turns an object, and why the component along r does not. (Guide: Figure 1; Practice Q7)
- I can explain the difference between r and the lever arm, and say when they are equal. (Guide: “Two other ways to read the same equation”; Practice Q3)
- I can explain why a force whose line of action passes through the axis exerts zero torque, however large it is. (Guide: Worked example 2; Practice Q1, Q4)
Skills
- I can calculate a torque with τ = rF sin θ, τ = rF⊥ and τ = r⊥F, and show that all three agree. (Guide: Worked example 1; Practice Q4)
- I can find the angle between r and F when the question gives a different angle, such as one to the horizontal. (Guide: Worked example 3; Practice Q4)
- I can draw a force diagram with each force at its point of application, and use it to find each torque about an axis. (Guide: Figure 2, Worked example 2; Practice Q6)
- I can derive a symbolic expression for a torque, such as the torque of gravity on a tilted rod. (Guide: Worked example 3; Practice Q5)
- I can label each torque as clockwise or counterclockwise about the chosen axis. (Guide: Worked example 2; Practice Q6)
Reasoning
- I can predict how a torque changes when F, r or θ changes, using a ratio of factors. (Guide: “Predicting changes”; Practice Q2, Q5)
- I can evaluate a claim about which of two pushes turns an object more, using both distance and angle. (Practice Q1, Q7)
- I can explain why changing the axis changes the torque a given force exerts. (Guide: Worked example 2; Practice Q6)
All ticked? Move on to Topic 5.4, Rotational Inertia, or return to the course roadmap.