ME 242 Lecture 20 03.23

# ME 242 Lecture 20 03.23 - ME 242 Dynamics Today's Key...

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1 ME 242 Dynamics March 23, 2009 Eric Wang Today’s Key Concepts Chapter 5: Multiparticle Systems Force Balance Linear Momentum Impulse-Momentum Multiparticle Systems • Center of Mass r = m i r i m i m i r i / G = 0 = r G Center of Mass • AKA “center of gravity” • Balance point m i r i / G = 0 Internal & External Forces • Internal forces (denoted by tilde) – Internal to the system – Not like ME241 or CE372 – Forces between particles – Force particle A exerts on particle B • External forces – Forces from outside the system – Force on particle B ˜ F AB F B Newton’s 2 nd Law • System with n -particles • For the i th particle (constant mass) j = 1 n ˜ F ji + F i = m i ˙ ˙ r i Force exerted by j th particle on i th particle Acceleration of i th particle External forces applied to i th particle

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2 Newton’s 3 rd Law • Using the fact: • Summing over all particles in the system: • Results in: ˜ F ji = ˜ F ij j = 1
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ME 242 Lecture 20 03.23 - ME 242 Dynamics Today's Key...

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