Lecture+14

# Lecture+14 - 440:221 Intro to Engineering Mechanics Statics...

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440:221 Intro to Engineering Mechanics: Statics Instructor: Alberto Cuitino TA: Pam Carabetta and Jingru Zhang Lecture 14 Fall 2009 1 Based on Textbook Material: Engineering Mechanics Statics, 12 th Edition, R.C. Hibbeler, Pearson 2010.

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440:221 Lectures quilibrium of a IGID ODY Equilibrium of a RIGID BODY School of Engineering, Fall 2009 2
440:221 Lectures opics to be covered Topics to be covered • How do we solve 2D equilibrium problems? • What is the difference between 2D and 3D? • Do we need a FBD in 3D? School of Engineering, Fall 2009 3

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440:221 Lectures teps for solving problems Steps for solving problems 1. If not given, establish a suitable x - y coordinate system. 2. Draw a free body diagram (FBD) of the object under analysis. 3. Apply the three equations of equilibrium (E-of-E) to solve for the unknowns. School of Engineering, Fall 2009
440:221 Lectures portant notes Important notes 1. If there are more unknowns than the number of independent equations, then we have a statically indeterminate situation. We cannot solve these problems using just statics. 2. The order in which we apply equations may affect the simplicity of the solution. For example, if we have two unknown vertical forces nd one unknown horizontal force and one unknown horizontal force, then solving F X = 0 first allows us to find the horizontal unknown quickly. 3. If the answer for an unknown comes out as negative number , then the sense (direction) of the unknown force is opposite to that assumed when starting the problem. School of Engineering, Fall 2009

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440:221 Lectures xample Given : The 4kN load at B of Example the beam is supported by pins at A and C . Find: The support reactions at A and C. Plan: 1. Put the x and y axes in the horizontal and vertical directions, spectively respectively. 2. Determine if there are any two-force members. 3. Draw a complete FBD of the boom. School of Engineering, Fall 2009 4. Apply the E-of-E to solve for the unknowns.
440:221 Lectures xample (cont ) FBD of the beam: A Y 5m 4 kN Example (cont.) A X A 1.5 m C B F 45 ° 1.5 m Note: Upon recognizing CD as a two-force member, the number of unknowns at C are reduced from two to one.

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Lecture+14 - 440:221 Intro to Engineering Mechanics Statics...

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