(11) Friction and Dynamics of Circular Motion

# (11) Friction and Dynamics of Circular Motion - Applying...

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Lecture 12 Applying Newton’s Laws

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Goals of Today’s Lecture Goals of Today’s Lecture Being able to apply Newton’s laws to any problem that is not insane.
EXAMPLE: Incline and pulley, with friction m 2m 35 ° Same system, but μ S = 0.2 and μ k = 0.1 What happens when the system is released?

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m 2m 35 ° N 2mg mg T T x y x Does the system move at all? net 2 sin35 0.15 F mg mg mg = - = Net force, along the direction of motion, without friction: S,MAX S f N μ = Maximum static friction force: μ S = 0.2 μ k = 0.1 It does not move! Motion without friction S 2 cos35 mg = 0.33mg =
ACT: Magnitude of friction ACT: Magnitude of friction What is the magnitude of the static force in the system we just studied? A. 0.15 mg B. 0.33 mg C. 0.40 mg For the system to be at rest, f S should cancel out the resultant of the remaining forces (the net force without friction). Option C is beyond the maximum possible value. Option B would produce a net force to the left along the incline! net , no f r ict ion S,max 0.15 0.33 F mg f mg = = m 2m N 2mg mg T T f S 35 °

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Example: Box on truck A box with mass m = 50 kg sits on the back of a truck. The
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## This note was uploaded on 03/27/2008 for the course PHYS 221 taught by Professor Herrera-siklody during the Fall '08 term at Iowa State.

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(11) Friction and Dynamics of Circular Motion - Applying...

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