# Engineering Mechanics - Mechanical Engineering (MCQ) questions and answers for Q. 11242

Q.  Which motion has magnitude of static frictional force directly proportional to normal reaction?
- Published on 18 Sep 15

a. Actual motion
b. Impending motion
c. Both a. and b.
d. None of the above

#### Discussion

• Sravanthi   -Posted on 16 Dec 15
- Impending motion can be defined as the motion which is just on the verge to occur but is not present. In this type of motion, the body is on the verge of slipping.

- In impending motion, the magnitude of limiting static frictional force is directly proportional to the magnitude of normal reaction.

Fs = μs R

here, μs is the co-efficient of static friction.

- The actual motion starts when the magnitude of force acting on a block becomes greater than frictional force and the magnitude of frictional force decreases to a value known as kinetic frictional force.

Fk = μk R

here, μk is the co-efficient of kinetic friction.

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