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 why only the component of a force perpendicular to r exerts a torque, and why a force aimed at the axis exerts none. (Guide: “Only the perpendicular component turns”; Practice Q3)
- I can define the lever arm as the perpendicular distance from the axis to the line of action, and show it on a diagram. (Guide: Figure 1; Practice Q4(c))
- I can explain why moving a force along its own line of action does not change its torque. (Practice Q5(e))
- I can explain why torques must always be stated about a named axis. (Guide: Worked example 3)
Calculation
- I can find the size of a torque three ways, rF sin θ, rF⊥ and r⊥F, and get the same answer. (Guide: Worked example 1; Practice Q1)
- I can work out r × F in unit-vector form and give its direction. (Guide: Worked example 2; Practice Q4)
- I can find the angle between r and F from their components and use it to check a torque. (Guide: Worked example 2; Practice Q4(b))
- I can add the torques of several forces about one axis with a stated sign convention. (Guide: Worked example 3; Practice Q5)
Representation and reasoning
- I can draw a force diagram with each force starting where it acts, including weight at the centre of mass. (Guide: “Force diagrams for rigid systems”; Practice Q5(a))
- I can use the right-hand rule to find the direction of r × F and link it to clockwise or counterclockwise turning. (Guide: “Torque as a vector”; Practice Q2)
- I can linearise data on force and angle to test whether a threshold torque is constant, and justify my conclusion with evidence. (Practice Q6)
- I can show that the net torque is the same about every axis only when the net force is zero. (Practice Q7)
All ticked? Move on to Topic 5.4, Rotational Inertia, or return to the course roadmap.