Chapter 9 Friction
Key Questions
At the end of this chapter you should be able to answer these questions.
- Evaluate dry friction problems across the three states of static-but-not impending, impending motion, and kinetic friction.
- Determine if a body will slip or tip and calculate the value of the force, angle or other parameter at which slipping or tipping will occur.
- Evaluate the amount of torsional moment needed to push a square-threaded screw to impending motion across various use cases.
- Compute the tension differential due to friction on either end of a flexible belt.
- Compute the forces or moment needed to overcome journal bearing friction.
- Compute the friction inherent in rotational disc friction with a hollow, solid, and circular arc contact surface.
Up until this point in the course, the effects of friction forces have been considered negligible. The reality is that friction not only slows things down (like friction between your skis and the snow when you ski down a hill) but is also the force which causes motion (like the friction between the rear wheel of your bicycle and the road causing you to move forward when you pedal). This chapter introduces various types of friction that occur on blocks, wedges, screws, belts, bearings, and rotating discs.