These notes are provide detailed information on the frictional force chapter in the Mind Action Series Physical Science Grade 12 textbook. These notes are colourful, have diagrams for further explanation and are very easily understood.
Friction
Chapter 2
Laws of Friction
Force of Static Friction (Fs) opposes motion when obj = stationery.
• Max force friction (Fs(max)) is = to Fapp when obj just starts to move
Force of Kinetic Friction (Fk) opposes motion when obj = moving & is = to
Fapp when obj moves w/ constant velocity.
Fn
Fapp 10N Fapp 15N Fapp 14N
Ffs(max) 15N
Fg Ffs 10N Fk 14N
Block is stationary Block just starts to move Block maintains constant velocity
coefficient shows how easily 1 surface slides past another
coeffi of FS (μs) = ratio of Fs(max) to FN
𝑓𝑓𝑠(𝑚𝑎𝑥) = 𝑢𝑠 ∙ 𝐹𝑁
coeffi of FK (μk) = ratio of FK to FN
𝑓𝑓𝑘 = 𝑢𝑘 ∙ 𝐹𝑁
Facts on Friction:
• Friction force betw 2 surfaces opposes their motion
• Friction force depend on type material & roughness of2 surfaces
• Friction force x depend on area of contact betw surfaces
• When surface @ rest, max stat friction force (Fs(max)) = dir prop to 𝐹𝑁
• When motion occurs, kinetic friction force (FK) = dir prop to FN & is
independent of the velocity
To Remember:
Low value 4 coefficient of friction indicates the friction force will = small.
μk is usually less that μs.
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