QUESTION 1 (5 marks)
Distinguish between static and kinetic friction
Static friction                                  Kinetic friction
It resists an object from moving. It is the resistance force while moving.
Generally, for the same pair of    For the same pair of surfaces, this force is
surfaces, this force                         weaker than static force.
is greater than kinetic force.
No energy conversion.                Conversion to heat, sound etc.
No erosion occurs.                         Generally liable to erosion.

QUESTION 2 (7 marks)
Under what circumstances does contact fatigue occur? What are the consequences arising out of this type of wear and how can it be limited?
Answer: The circumstances:
1. Where the contact area is very small.
2. Contact area seems a point or line that enlarges to an area with increase in loading.
3. Two curved surfaces are pressed together where a subsurface plastic strain is generated with increasing cycles until a crack is produced.
4. The higher the traction or tangential force, the more probable the occurrence of contact fatigue.
In general the consequences are:
1. Cracking.
2. Pitting.
3. Flaking of the surface material.
To limit these effects
1. Lubricants are applied.
2. Bearing loads are reduced or distributed among more elements.
3. Surface hardening treatments are used.
4. Scatter is reduced through ensuring the homogeneity of material microstructure, high quality surface finish, improving rolling element precision.
5. Compressive residual stress may be imposed by short peening, nitriding and burnishing.
QUESTION 3 (8 marks)
What is hydrodynamic lubrication? What are the parameters on which the shift from one lubrication regime to the other based on?
Answer: Hydrodynamic lubrication occurs when a shaft rotating in a bearing floats over a layer or thick film of the lubricant fluid existing between the bearing material and the shaft itself so that the shaft is not in contact with the bearing

Measurement System Behavior and Probability &amp; Statistics 1. A...

Measurement System Behavior and Probability & Statistics 1. A...