PHY 2004 lectures 1-12

# PHY 2004 lectures 1-12 - PHY 2004 LECTURES 10-12...

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PHY 2004 LECTURES 10-12 EQUILIBRIUM Chapter 8. No motion ( OR constant motion i.e. no acceleration) Vector sum of forces =0 I.e. in figure to right F 1 + F 2 = F UP In figure below, Equilibrium requires For horizontal direction; T1 = T2 cos 53 = 0.6T2 For vertical direction; T2 sin53 =2 00, OR 0.8T2 =200 Solve T1= 150 N

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Turning effect Measure of turning or twisting (rotational or angular) motion Torques must cancel Torque = d * perpendicular component of force to axis d = dF Has a sense of rotation about P: clockwise (+) or anticlockwise (-) Equilibrium: Sum of all torques about ANY point in system must =0 E.g seesaw Sum of torques =0 W1 *a1 +W2*a2 =0

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PHY 2004, Lectures 8-9 ENERGY, WORK Work W = FxD. D =distance in the same direction as the force Work by gravity F=mg If move against gravity do positive work W =mgh This energy is stored, e.g placing a mass on a shelf at height h Can recover this POTENTIAL energy Knock mass off shelf. Object gains KINETIC energy Use V F 2 = 2gh to show final kinetic energy K =(1/2)mV 2
LECTURE 7 PHY 2004 FRICTION Force of friction proportional to force NORMAL to motion μ = coefficient of friction f= μ W Rubber on concrete μ 0.8 Steel on steel 0.07 Skater on ice 0.02

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Static versus sliding friction Object does not move until F applied overcomes static friction Inclined plane Force normal to plane F = Wcos θ Friction f = μ Wcos θ SLIDES when Wsin θ =f OR tan θ = μ
Gravity Force 1 2 2 Gm m F R G is universal constant (same everywhere)

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