sy06_sept24_07hc (1)

# sy06_sept24_07hc (1) - Physics 207 Lecture 6 Pg 1 Physics...

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Unformatted text preview: Physics 207: Lecture 6, Pg 1 Physics 207, Physics 207, Lecture 6, Sept. 24 Lecture 6, Sept. 24 Agenda: Agenda: Assignment: For Wednesday read Chapter 7 Assignment: For Wednesday read Chapter 7 ● MP Problem Set 3 due Wednesday MP Problem Set 3 due Wednesday ● MP Problem Set 4 available soon MP Problem Set 4 available soon ● MidTerm Thursday, Oct. 4, Chapters 1-7, 90 minutes, 7:15-8:45 PM MidTerm Thursday, Oct. 4, Chapters 1-7, 90 minutes, 7:15-8:45 PM ● Chapter 5 Chapter 5 Friction (a external force that opposes motion) • Chapter 6 (Dynamics II) Motion in two (or three dimensions) Frames of reference Physics 207: Lecture 6, Pg 2 Friction... Friction... ● Friction is caused by the “microscopic” interactions between the two surfaces: Physics 207: Lecture 6, Pg 3 A special contact force, friction A special contact force, friction ● What does it do? It opposes motion ! Parallel to a surface Perpendicular to a surface N Normal force ● How do we characterize this in terms we have learned? A resulting force in a direction opposite to the direction of motion (actual or implied )! m a F APPLIED f FRICTI ON m g N i j j Physics 207: Lecture 6, Pg 4 Sliding Friction (i.e., with motion) Sliding Friction (i.e., with motion) ● Direction: A force vector ⊥ to the normal force vector N N ● Magnitude: | f f K | is proportional to the magnitude of | N N | | f f K | = μ K | N N | ( = μ K | m g g | in the previous example) Physics 207: Lecture 6, Pg 5 Case study ... big F Case study ... big F ● Dynamics: x-axis i : ma x = F- μ K N y-axis j : ma y = 0 = N – mg or N = mg so F- μ K m g = m a x m ax F m g N i j j μ K mg v f k f k Physics 207: Lecture 6, Pg 6 Case study ... little F Case study ... little F ● Dynamics: x-axis i : ma x = F- μ K N y-axis j : ma y = 0 = N – mg or N = mg so F- μ K m g = m a x m a x F m g N i j j μ K mg v f k f k Physics 207: Lecture 6, Pg 7 Static Friction... Static Friction... F F applied m g g N N i j j f S ● So far we have considered friction acting when something has a non-zero velocity We also know that it acts in fixed or “static” systems: ● In these cases, the force provided by friction depends on the forces applied on the system (magnitude: f s ≤ μ s N ) ● Opposes motion that would occur if μ s were zero Physics 207: Lecture 6, Pg 8 Static Friction... Static Friction... ● Just like in the sliding case except a = 0 . i : F applied- f S = j : N = mg F F applied applied m g g N N i j j f S ● While the block is static: f S = F applied (unlike kinetic friction) Physics 207: Lecture 6, Pg 9 Static Friction... Static Friction... F m g N i j j f S ● The maximum possible force that the friction between two objects can provide is f MAX = μ S N , where μ s is the “ coefficient of static friction ”....
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sy06_sept24_07hc (1) - Physics 207 Lecture 6 Pg 1 Physics...

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