Download Motion in Two Dimensions

Newton’s Laws of Motion
Friction
Friction
“Everyone knows about friction but we do
not have a fundamental theorem of
friction, and cannot predict friction
between two surfaces.”
Robert Carpick
University of Wisconsin-Madison
Milwaukee Journal Sentinel July 23, 2006
Friction
• Friction is __________ to motion caused by
an ___________ with surroundings
• The motion is on a surface or through a
___________ medium (e.g., water and air)
• Force of static friction, fs, acts on an object
when its velocity is ______
• Force of kinetic friction, fk, acts on an object
when its velocity is ____ ______
Microscopic View of Friction
• May be mechanical
in nature
• May be electrical in
nature
Coefficient of Friction, μ
•
•
•
•
Coefficient of Static Friction, μs
Coefficient of Kinetic Friction, μk
μk ≤ μs
Force of friction is proportional to μ and the
________ force
f s  s n
f k  k n
Graph of Frictional Force, f