ME 242 Lecture 7 02.04

ME 242 Lecture 7 02.04 - ME 242 Dynamics February 4 2009...

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1 ME 242 Dynamics February 4, 2009 Eric Wang Today’s Key Concepts Relative motion • Relative position • Relative velocity • Relative acceleration • Degrees of Freedom • Constraints Relative Position r A / O = r B / O + r A / B Velocities d dt XYZ r A / O = r B / O + r A / B ( ) d dt XYZ r A / O = d dt XYZ r B / O + d dt XYZ r A / B r A / O = r B / O + r A / B Absolute Velocities d dt XYZ r A / O = d dt XYZ r B / O + d dt XYZ r A / B d dt XYZ r A / O = v A / O = v A d dt XYZ r B / O = v B / O = v B Which Train is Moving?
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2 Relative Velocity Imagine: 1. A & B moving at same velocity 2. A moving towards stationary B 3. B moving towards stationary A d dt XYZ r A / B = v A / B Accelerations r A / O = r B / O + r A / B v A = v B + v A / B a A = a B + a A / B Common Mistake r A / O = r B / O + r A / B r A / O = r B / O + r B / A Learn the nomenclature & draw the picture instead of memorizing the formula! Flipping it around
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ME 242 Lecture 7 02.04 - ME 242 Dynamics February 4 2009...

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