ME 221Lecture 221 ME 221 Statics Lecture #22 Sections 5.1 – 5.4

ME 221Lecture 222 Homework #8 Chapter 9 problems: –42, 43, 50 & 55 Chapter 5 problems: –11, 13, 16, 20, 24 & 25 –See Blackboard for additional information Due Wednesday, October 30

ME 221Lecture 223 Quiz #5 Friday, March 14

ME 221Lecture 224 Chapter 5 Equilibrium of Rigid Bodies

ME 221Lecture 225 Equilibrium of Rigid Bodies Equilibrium equations Free body diagrams Modeling supports Problems

ME 221Lecture 226 Newton’s Second law states that if there is a net force acting on the body, then this will cause motion of the rigid body. If there is no motion, then the object is said to be in equilibrium. Equilibrium of Rigid Bodies

ME 221Lecture 227 Equilibrium Equations When the force system is replaced by a resultant force and moment that are zero, the rigid body is in equilibrium. The moment equation is new and differentiates particle from rigid body equilibrium.

ME 221Lecture 228 Examples of supports: rollers smooth surfaces rockers clamps slots collars cables links fixed Supports for Rigid Bodies If a rigid object is subjected to some set of forces but does not move, then its motion could be restrained by a normal force exerted by the ground, a wall or from fixing the object with some support.

ME 221Lecture 229 Support Reactions If the support prevents translation in a given direction, then a force is developed on the member in that direction. Likewise, if a rotation is prevented, then a couple moment is exerted on the member. See Figures 5.1 and 5.2 (supports for rigid bodies subjected to 2-D and 3-D force systems)

ME 221Lecture 2210 Free Body Diagram Draw the body separate from all other bodies (including ground). Draw the magnitudes and directions of all external forces acting on the body. –No need to scale arrow size Include necessary dimensions of the body –Dimensions are needed for summing moments Draw the positive sense of the coordinate system used to write out equilibrium equations –Include: applied loads, reactions due to supports, and the weight of the object.

ME 221Lecture 2211 Importance of FBD The FBD is at least half of an equilibrium problem.

ME 221Lecture 2212 Chapter 5 Equilibrium Examples