Lecture 14- friction wear and lubrication

Question 1

are surfaces perfectly flat? if not, explain why

Answer 1

no, all surfaces have asperities and they meet at those points. real contact area is much lower than measured area

Question 2

What are amonton’s 3 laws of friction?

Answer 2

friction force is proportional to normal force
F is independent of area of contact
F is independent of sliding speed

Question 3

define adhesive wear

Answer 3

adhesion at the work hardened junctions causes material to shear off when surfaces slide

Question 4

define abrasive wear

Answer 4

this happens when the asperities of the harder material grind off junctions of the weaker material

Question 5

why do we use lubrication?

Answer 5

it allows for easy shear between surfaces and reduces coefficient of friction

Question 6

When do we use hydrodynamic lubrication?

Answer 6

for higher-performance applications

Question 7

where is hydrodynamic lubrication used?

Answer 7

bearings
brakes
bike and car tyres
gears
friction welding