Topic: Engineering Mechanics
Which of the following statements regarding governing the friction between dry surfaces are correct?
1. The friction force is dependent on the velocity sliding.
2. The friction force is directly proportional to the normal force.
3. The friction forced is dependent on the materials of the contact surfaces.
4. The friction force is independent of the area of contact.
Select the correct answer using the codes given below:
- A. 2, 3 and 4
- B. 1 and 3
- C. 2 and 4
- D. 1, 2, 3 and 4
Answer: A. 2, 3 and 4
Explanation: According to the laws of dry friction: (1) Force of friction is directly proportional to the normal load. (2) It is independent of the area of contact. (3) It depends on the nature of the materials in contact. (4) It is independent of the velocity of sliding. Therefore, statements 2, 3, and 4 are correct.