ENGR& 214: Concept Questions
Friction
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1. What is friction?
2. What are the types of friction? Briefly explain each type.
3. From the previous question, which type of friction is most relevant to statics?
4. In what direction does friction act on a body?
5. What is the physical cause of friction between surfaces?
6. Explain the difference between the following types of Coulomb friction: Static, but not
impending, impending motion, and kinetic friction.
7. What is the friction coefficient and physically what does it represent?
8. What is the range of values the friction coefficient can take?
9. Explain how the friction force on an object that starts at rest changes as the applied force
increases. You may include a diagram to help explain the process, but also write it in your
own words.
10. What is the value of the friction force when motion of the body is impending?
11. What happens when the friction force for impending motion is exceeded?
12. Why is the force for impending motion almost always higher than the kinetic friction force?
What are the physical implications of this?
13. What force acting on the body are the friction equations for impending motion and kinetic
friction both related to?
14. How can you determine which type of friction force the problem wants you to use?
15. When “slipping is about to occur” would you use the static friction force or the kinetic friction
force in your analysis of the problem?
16. What is the angle of static friction and how is it determined?
17. Why does the normal force act at a point away from the centroid like in the diagram below
when dealing with friction in an equilibrium problem?
18. Explain the uses for low friction wedges and high friction wedges.
19. Explain the process of solving block and wedge friction problems.
20. How is solving block and wedge friction problems similar to how we solved frames and
machines? How is it different?
21. In a 2-D friction problem what are the two possible ways a body may move if it is at the point
of impending motion? Explain what each of these means about how the body will move.
22. What is the condition under which a body will slip and what condition will the body tip?
Because it depends if the body its slip or top
23. What is the process for determining whether a body will slip or tip?
The higher the force is being applied the most possibility to top
24. In 2-D problems involving friction, you are still limited to only 3 equations of equilibrium. If
you have more than 3 unknowns in the problem, what other equations can be used to help
solve the extra unknowns?
You can found the coefccient of friction to find the other unknowns
25. Can you assume the direction of a friction force and use math to determine the direction of
force like with support reactions or do you have to determine the correct direction of the
friction force on the FBD from the information given in the problem by inference of the
physical situation? Explain your answer.
