Friction and Lubrication

Question 1

first-order law of friction

Answer 1

F = µN

Frictional force independent of the apparent area of contact between sliding surfaces!

Question 2

define asperities.

Answer 2

projections on surfaces at a molecular scale, which cause friction as shear stresses in asperities opposes sliding

Question 3

describe the deformation of asperities for different loads

Answer 3

at very low loads, asperities (irregularity in surfaces on a molecular level) deform elastically where they touch

for realistic loads, extensive plastic deformation takes place at the tips –> adhesion
–> causes heating and wear, and in extreme cases, binding of surfaces

Question 4

what does lubrication do?

Answer 4

prevents adhesive contact between surfaces – thin layer of oil shears easily when force is applied, lowering µ

Question 5

feature of elastohydrodynamic lubrication

Answer 5

a lubrication regime resulting in no asperity contact