Plan the investigation
What students will do
Start with a guided comparison, then plan an investigation, analyze a graph, and check a prediction.
- Locate the transition. Compare resting and sliding trials at several incline angles with the same friction settings.
- Design and collect. Choose at least five static-friction coefficients. For each one, bracket the onset of sliding while keeping kinetic friction fixed.
- Analyze the relationship. Choose transformed graph quantities that produce a straight line and evaluate the critical-angle model.
- Explain and predict. Use force balance and the transition intervals to predict and test the critical angle for an unused coefficient.
What students will learn
- Relate the onset of sliding to limiting static friction.
- Bracket a threshold rather than assume an exact transition.
- Test a trigonometric model using transformed data.
Common misconception
Does doubling static friction double the critical angle?
The model connects the coefficient with the tangent of the critical angle, rather than angle alone.