Discussion session3.pdf - ENGR 30 STATICS Discussion...

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1 ENGR 30 STATICS Discussion Session 3 Fall 2018
2 About This Session: Moment of a Force About a point About an axis Couple and Equivalent Force Systems
3 Fundamental Concepts Moment of a Force About a Point Moment (M) is the tendency of a force to rotate an object about a point that is not on the line of action of the force. (sometimes called torque) ? 𝑂 = 𝐹 ⋅ ? F d d is the moment arm or the perpendicular distance from point O to the line of action of the force Moment of a force scalar definition Clockwise: Negative Counterclockwise: Positive M
4 Sample Problem Scalar method x y It is known that the connecting rod AB exerts on the crank BC a 2.5-kN force directed down and to the left along the centerline of AB. Determine the moment of the force about C. F =2.5 kN A(0,0) ? ?1 = 𝐹 ? ? ? = (2.5 × 7 25 ) × 88 = 61.6? ⋅ ? ? ?2 = 𝐹 ? ? ? = (2.5 × 24 25 ) × 0 = 0 ? ? = ? ?1 + ? ?2 = 61.6? ⋅ ? F x F y C(0,-88)
5 Fundamental Concepts Moment of a Force About a Point Concept of the moment of a force vector about a point requires the understanding of the vector product or cross product . The moment of F about O is defined as 𝐌 𝐎 = 𝐫 × 𝐅 1.Line of action of V is perpendicular to plane containing P and Q .

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