Physics 121 10/6/10 Prof. E. F. Redish 1 10/6/10 1 Physics 121 10/6/10 6 Physics 121 BAstaticABBABANff=μmaxBAkineticABBANf=μstaticABkineticABμμ10/6/10 8 Physics 121 Start from rest Increase force until box starts moving Pull so it goes at a constant speed Graph: position velocity acceleration net force applied force friction forcePhysics 121 10/6/10 Prof. E. F. Redish 2 10/6/10 10 Physics 121 10/6/10 11 Physics 121 10/6/10 15 Physics 121Physics 121 10/6/10 Prof. E. F. Redish 3 10/14/09 16 Physics 121 90- 90 opp adj hyp Although opp, adj, and hyp all depend on the size of the triangle, the ratios opp/adj, opp/hyp, and adj/hyp only depend on itsshape (that it, on ) . 10/14/09 17 Physics 121 90- 90 opp adj hyp sin=opphypcos=adjhyptan=oppadjPythagorian theorem: adj()2+ opp()2= hyp()2orsin2+ cos2= 1Physics geometry heuristic: If you are drawing a diagram that is controlled by a single angle , and the rest of the lines are constructed as perpendiculars to the original or later lines, then the only angles in the diagram are , 90-, and 90 –- and it’s easy to tell which is which. 10/14/09 18 Physics 121 block sliding down a ramp y x y x WEB Wy Wx NRBPhysics 121 10/6/10 Prof. E. F. Redish 4 10/14/09 19 Physics 121 Wy Wx NRB WEB ? ? 10/14/09 20 Physics 121 T T k1 (large) k2 (small) 10/7/09 21 Physics
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