EF 202, Module 2, Lecture 3 1 Albert Einstein, when asked to describe radio, replied: "You see, wire telegraph is a kind of a very, very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? And radio operates exactly the same way: you send signals here, they receive them there. The only difference is that there is no cat." EF 202, Module 2, Lecture 3 Pulleys, Distributed Loads, and Equilibrium in Three Dimensions EF Week 7 EF 202, Module 2, Lecture 3 3 Pulleys Negligible mass Negligible friction at pin Cable does not slip Cable tension constant EF 202, Module 2, Lecture 3 4 Problem 3-28 For equilibrium, what is F as a function of the angle ? EF 202, Module 2, Lecture 3 5 Distributed Force: Resultant Height of load diagram is force per unit length. Total force: area under load diagram. Location of line of action: centroid of load diagram. EF 202, Module 2, Lecture 3 6 Distributed Force: Examples EF 202, Module 2, Lecture 3 7 Example EF 202, Module 2, Lecture 3 8 Distributed Force: Resultant EF 202, Module 2, Lecture D Connections ConnectionUnknowns Cable1 Smooth1 Roller1 or 2 Ball & Socket3 Journal Bearing 4 Hinge5 Fixed6 See Table 5-2, pp Supports - 3 D EF 202, Module 2, Lecture D Systems We can sum forces in any three directions to generate three independent equations. We can sum moments about any point to generate three independent equations. We can have six unknowns and still solve for all. EF 202, Module 2, Lecture 3 13 Problem Solving Strategy 1. Identify ALL forces and moments acting on the body by making a free- body diagram (FBD). 2. Invoke Newtons First Law. (Sum forces and moments.) 3. Solve. EF 202, Module 2, Lecture 3 14 Problem 5-72 Ball and socket at A, roller at B, cable at C. Find all reactions. EF 202, Module 2, Lecture 3 15 EF 202, Module 2, Lecture 3 16 Problem 5-99 Fixed at A. Find all reactions EF 202, Module 2, Lecture 3 17 EF 202, Module 2, Lecture 3 18 Problem 5-86 Journal bearing at A. Thrust bearing at B. No moment reactions at A, nor at B. Find P and all reactions. 17 EF 202, Module 2, Lecture 3