Friction topics include: Dry friction characteristics and problems, wedges, frictional forces on screws, flat belts, pivot bearings and disks, journal bearings and rolling resistance. Friction is a force that resists motion when an object's surface comes into contact with another surface. It's a retarding force that always acts in the opposite direction of motion.  In engineering mechanics, friction is a crucial concept that represents the energy lost when two surfaces slide or roll over each other. This energy is typically lost as heat, so engineers try to minimize friction.  The maximum... Show more

Friction topics include: Dry friction characteristics and problems, wedges, frictional forces on screws, flat belts, pivot bearings and disks, journal bearings and rolling resistance.

Friction is a force that resists motion when an object's surface comes into contact with another surface. It's a retarding force that always acts in the opposite direction of motion. 
In engineering mechanics, friction is a crucial concept that represents the energy lost when two surfaces slide or roll over each other. This energy is typically lost as heat, so engineers try to minimize friction. 
The maximum frictional force between two surfaces is FMAX=μR, where μ is the coefficient of friction and R is the normal reaction between the two surfaces. 

There are four main types of friction: Static friction, Sliding friction, Rolling friction, Fluid friction. 
Friction reduces the mechanical advantage of a machine, which is the ratio of output to input.

Dry friction, also known as Coulomb friction, is a force that occurs when two solid surfaces in contact try to move relative to each other. The friction force opposes the relative velocity direction and depends on the normal force that acts on the body. 

Dry friction is subdivided into static friction and kinetic friction:
Static friction: Also known as "stiction", this occurs between non-moving surfaces.
Kinetic friction: This occurs between moving surfaces. 
Dry friction can be encountered in daily life, such as when walking on the ground, sliding an object across a table, or rubbing hands together. 

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Engineering Mechanics Practice Test: Friction

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25 Questions

1. We show the net forces by the help of __________ forces.

RotationalHelicalResultantsLinear

2. Coplanar forces are not easily simplified in the simplification of the force and couple system in the calculations of forces in the journal bearings.

MaybeFalseTrueDon't Know

3. At what conditions does the Coulomb friction occur between the surfaces in contact of collar bearings or pivots?

When there is no cohesive fluidWhen there is no lubricating fluidWhen there is no adhesive fluidWhen there is no friction fluid

4. In the screw collinear forces act, what is a collinear system of forces?

Forces cannot form a collinear system of forces, it is not possibleThe force system having all the forces perpendicular to each otherThe force system having all the forces emerging from a single pointThe force system having all the forces parallel to each other

5. The angle of the inclination of wedge over which the block is sliding and is experiencing the kinetic friction is determined by which of the following trigonometric function?

SecantSineTangent InverseCosine

6. There are mainly two types of forces which are being stated in the free body diagram, and they are generally the resultant of various forces which are being acted over the body. Which are they?

Normal and FrictionalVertical and FrictionalNormal and FractionalNormal and Vertical

7. In the calculations of the bearings, we often use vector math. So for those systems which of the following is true?

j x i = -jk x j = -ii x i =1k x k = 1

8. In screws there is an application of two and three force members. The basic difference between the two and the three force members used is ___________

The former is parallel and the latter is perpendicularThe former is collinear and the latter is parallelThe former is acting on two points in the body while the latter is on three pointsThe former is perpendicular and the latter is collinear

9. The normal forces and the forces of friction are collinear.

FalseMaybeTrueDon't Know

10. Which one is not the condition for the equilibrium in free body diagram for calculation of the normal forces, consider all forces to be straight and linear?

∑Fy=0∑F≠0∑Fx=0∑Fz=0

11. For equilibrium the normal forces acts in which direction in the free body diagrams?

Horizontally RightVertically UpwardHorizontally LeftVertically Downward

12. Determine the horizontal force acting in the given figure.

40cos308cos3060cos3080cos30

13. To know the rotations involved in the journal bearings we use right handed coordinate system, in that system which of the following is followed (consider the mentioned axis to be positive)?

Thumb is y-axis, fingers curled from x-axis to z-axisThumb is z-axis, fingers curled from y-axis to x-axisThumb is z-axis, fingers curled from x-axis to y-axisThumb is x-axis, fingers curled from z-axis to y-axis

14. Determine the moment about the point Q by the force shown as 400N.

98.6kN-98.6kN-98.6iN-98.6jN

15. The coefficient of static friction does depend upon the surface on which the body is being slide.

FalseDon't KnowMaybeTrue

16. The coefficient of friction is generally determined by ____________

ExperimentsWritten over the BodyWeighing the bodyMeasuring length of the body

17. The collar bearings are generally used in __________

MachinesBeltsBeamsColumns

18. The moment is the cross product of which two vectors in the calculations of the journal bearings?

Radius and Force scalarsRadius and Force vectorsForce and Radius vectorsForce and Radius scalars

19. Which statement is correct about the vector F acting parallel to the direction of the motion of the rolling body?

F= Fsin β + Fcos α + FcosγF= Fcos β + Fcos α + FsinγF= Fcos β + Fsin α + FcosγF= Fcos β + Fcos α + Fcosγ

20. The kinetic friction is applied when the body is __________

Just stoppedMovingStoppedJust started to move

21. The blocks of heavy weights are being able to lift from the help of the wedges.

TrueDon't KnowMaybeFalse

22. For equilibrium, the normal forces act in which direction in the free body diagrams if they are constructed for the friction part calculations?

Horizontally LeftHorizontally RightVertically UpwardVertically Downward

23. As we are using vector math to solve for the unknown forces in the free body diagrams, what is k.i?

∞1-10

24. In the simplification of the forces for the free body diagram, the net force acts at the ___________ of the loading body.

CentroidThe centre axisThe baseThe corner

25. We first make equilibrium equations of the sections involving the collar bearings or pivots by considering all the three dimensional forces acting on the section chosen and then the free body diagram is made and solved.

The first part of the statement is true and other part is true tooThe first part of the statement is false and other part is false tooThe first part of the statement is false and other part is trueThe first part of the statement is true and other part is false