Spool/String Direction Trick
Spool can roll toward or away from the pull.
Teaching & key ideas
What you do: Pull string at different angles along table/floor.
What students see: Spool can roll toward or away from the pull.
Why it works: Torque direction depends on the line of force relative to the contact point.
Question to ask: How can pulling one way make it roll another?
Lesson flow
Predict → demonstrate → observe → briefly explain → ask: How can pulling one way make it roll another?