The Midterm Exam for Tribology UPDATED ACTUAL Exam Questions and CORRECT Answers

The Midterm Exam for Tribology UPDATED
ACTUAL Exam Questions and CORRECT
Answers
What daily activities would be impossible without friction - CORRECT ANSWER -
hiking up a mountain, stopping at a stop sign, walking


Who are the founding fathers of friction? - CORRECT ANSWER - 1) Leonardo da Vinci
2) Guillaume Amonton
3) Charles-Augustin Coulomb
4) Osborne Reynolds


What is friction? - CORRECT ANSWER - the resistance to relative motion between two
surfaces.
without friction objects would slide past each other at a constant speed forever


What are the two types of friction? - CORRECT ANSWER - Static friction and kinetic
friction which can be divided further into dry and lubricated friction


What is lubricated friction - CORRECT ANSWER - liquid film between the two surfaces
in contact


what is dry friction - CORRECT ANSWER - no fluid film between the two surfaces



What are the four major sources of friction? - CORRECT ANSWER - roughness, plastic
deformation, ploughing, and hysteresis


In addition to adhesion plastic deformation, ploughing, and hysteresis give rise to friction

,Which friction would be higher static(resting) or dynamic(kinetic)? - CORRECT
ANSWER - static friction is greater than kinetic friction


Static: initial resistance to start motion


Kinetic: the resistance to maintain the motion


What are the causes of static friciton? - CORRECT ANSWER - 1) The surfaces form
strong chemical bonds/micro welding at the asperities and a much higher force is needed to
break these bonds and start the motion


2) relative motion might cause the asperities to chip/break loss debris between the layers adding
more friction


3) metals: deformation due to creep due to long static contact. The creep increases the contact
area and the friction force


Relationship between creep and temperature - CORRECT ANSWER - creep occurs more
at higher temperatures, more creep more friction


even room temp can be considered an "elevated temperature" for some materials resulting in
more creep and friction


Static Friction: Capillary Forces - CORRECT ANSWER - Due to water accumulating
from the environment around the contact points


at the nano asperity level there will be a meniscus bridge of water


How does Hydrophobic/Hydrophilic relate to static friction - CORRECT ANSWER -
nature of the surface will impact the capillary forces and relate to the surface energy

, Static Friction: Interlocking - CORRECT ANSWER - the surface asperities from both
surfaces will shrink in the valleys in between as time goes by-->increasing interlocking


More force needed to break surfaces apart(untangle/break the interlocked surfaces)


What is the friction due to asperity interlocking called? - CORRECT ANSWER - Coulomb
Friction


How many laws of friction are there - CORRECT ANSWER - three



Who made the first two laws of friction - CORRECT ANSWER - Guillaume Amonton



Who made the third law of friction - CORRECT ANSWER - Coulomb



First Law of Friction - CORRECT ANSWER - the friction force is proportional to the
normal load.


Second Law of Friction - CORRECT ANSWER - the friction force is independent of the
apparent area of contact


Third Law of Friction - CORRECT ANSWER - friction force is independent of the sliding
velocity


definition of friction coeff


When are the laws of friction most likely to be invalid - CORRECT ANSWER - all laws
are for dry sliding and are probably invalid under lubricated/wet contact or also invalid for
rolling contact