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ME 242 Lecture 10 02.11

# ME 242 Lecture 10 02.11 - ME 242 Dynamics Today's Key...

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1 ME 242 Dynamics February 11, 2009 Eric Wang Today’s Key Concepts Chapter 3: Kinetics of a Particle • Newton’s 2 nd law: In Polar Coordinates F = d dt mv ( ) Polar Coordinates sign with the understanding that we always mean the sum F = ma Vector form F r e r + F θ e + F z k = m ( a r e r + a e + a z k ) Scalar form F r = m ˙ r r ˙ 2 ) F = m (2˙ r ˙ + r ˙ ˙ ) F z = m ˙ ˙ z Note Coupling causes changes in both r and causes changes in both r and F r F F r = m ˙ r r ˙ 2 ) F = m r ˙ + r ˙ ˙ ) F x = m ˙ ˙ x F y = m ˙ ˙ y Coupled Not-coupled Interchangeable Nomenclature F r = m ˙ r r ω 2 ) F = m r + r α ) F z = m ˙ ˙ z F r = m ˙ r r ˙ 2 ) F = m r ˙ + r ˙ ˙ ) F z = m ˙ ˙ z Example (prob. 3.2.6) Given: (constant) when t = 0 L = 1m • Friction Find: • Time when mass starts moving μ = 0.5 ˙ ˙ = 4 rad s 2 ˙ = 0

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2 Always start with FBD=IRD • FBD • IRD e r e θ Write Eqns based on the Diagrams Substitute in the Givens

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ME 242 Lecture 10 02.11 - ME 242 Dynamics Today's Key...

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