1. Free Body Diagrams Outline Free Body Diagram Quiz

2. Mass The slope of the line on the acceleration versus force graph indicates how reluctant something is to change its motion A steep slope indicates that the object has little mass (need less force for a given acceleration) A gentle slope indicates that the object has a lot of mass (need more force for a given acceleration) The slope of “F vs a” gives the mass, and steep slope = large mass Why is inertial mass the same as gravitational mass?

3. Free Body Diagrams This is where the physics gets done, the rest is just algebra and calculus An important tool for understanding motion The following steps will help you get it right every time

4. Identifying Forces Identifying forces  Identify “the system” and “the environment.” The system is the object whose motion you wish to study; the environment is everything else.  Draw a picture of the situation. Show the object—the system—and everything in the environment that touches the system. Ropes, springs, and surfaces are all parts of the environment.  Locate every point where the environment touches the system. These are the points where the environment exerts contact forces on the object.  Name and label each contact force acting on the object. There is at least one force at each point of contact; there may be more than one. When necessary, use subscripts to distinguish forces of the same type.  Name and label each long-range force acting on the object.

5. Drawing a free-body diagram  Draw a coordinate system. Use the axes defined in your pictorial representation. The axes may be tilted, as for motion along an incline.  Represent the object as a dot at the origin of the coordinate axes. This is the particle model.  Draw vectors representing each of the identified forces. Be sure to label each force vector.  Draw and label the net force vector Draw this vector beside the diagram, not on the particle. Then check that it points in the same direction as the acceleration vector on your motion diagram.

6. Demo Draw the free body diagram for a bouncing ball: 1.At the very top of its path 2.At the very bottom of its path

7. Demo Draw the free body diagram for a mass that is being supported by: 1. One string 2. Two stings

8. Demo Draw the free body diagram of a sled being pulled over frictionless snow with a rope at some angle to the horizontal.

9. Demo Draw the free body diagram for two blocks connected by a rope and being pulled over a rough surface.

10. Demo Draw the free body diagram for a mass hanging from a ceiling and supported by two strings.

11. Do for next class: Read: Sections 5.1, 5.2 Suggested problems: 5.3, 5.5a, 5.7