6 FRICTION


A


Without lubrication, this sliding would quickly cause overheating.


C


Corrosive wear, which is a common cause of car engine inefficiency, often damages the cylinder head itself.


E


B


Oil is passed through a filter in which all dust and dirt which might cause friction is removed.


D


In addition to polishing key components, designers reduce friction in two ways.


Having cleaned the oil, the lubrication system pumps it to the relevant parts of the engine.


Table 1: Br eaking a complex sentence into constituent parts Main S


Main V A this sliding B Main O/C


would (quickly) overheating cause


Other V + S/O/C


Adv. phrases


and the engine without lubrication would seize


Friction & wear: A study – tribology


• tribology = science and technology of interaction between surfaces in rel. motion


• surfaces appear smooth BUT under microscope, still uneven


• ... contact force spread over rel. v. small area • ... intense pressure @ contact points wear


• ... when 2 surfaces brought together actual contact only at ridges


• Tribology concerned w. 3 types of wear: - adhesive = surface worn away, e.g., sole of shoe can seize,


i.e., lock together - abrasive = 1 material harder scratches other, softer one - erosive = hard particles between surfaces pitting.


• How reduce wear? • Lubrication


e.g., mineral oils, other very low shear strength materials


• Some situations, friction necessary: e.g., skis friction = help & hindrance:


one hand, reduce friction (shops apply wax to bottom of skis) skiers travel v. quickly


other hand, skier turns & digs edges of skis into snow friction must be sufficient to turn w. control.


51


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