1. An Introduction to Statics Unit 3, Presentation 4

2. What is Statics?  Statics: The study of the forces associated with objects at equilibrium with each other.  No motion with objects in equilibrium  All accelerations are equal to 0  All net forces are equal to 0

3. Statics Example Problem A traffic light of mass 50 kg hangs from a vertical cable tied to two other cables that are fastened to a support (see below). The upper cables make angles of 37.0° and 53.0° with the horizontal. Find the tension in each of the three cables. 37.0°53.0° T1T1 T2T2 T3T3

4. Statics Example Problem Cntd. Consider drawing free body diagrams for two objects: the stop light and the knot connecting the three cables. FBD for the Stop LightFBD for the knot mg T3T3 T3T3 T2T2 T1T1 Must break down vectors T 1 and T 2 into x and y components.

5. Statics Example Problem Cntd. T1T1 37.0° T 1x T 1y T2T2 T 2x T 2y 53.0°

6. Statics Example Problem Cntd. x-direction y-direction Note: Two equations, two unknowns…solve a system of linear equations. We’ll use substitution.

7. Another Statics Example Problem A sled is tied to a tree on a frictionless, snow-covered hill, as shown below. If the sled weighs 77.0 N, find the force exerted by the rope on the sled and the magnitude of the normal force exerted by the hill on the sled. 30.0° mg FnFn T

8. Another Statics Example Problem x-directiony-direction