This chapter is strictly about how to draw those crazy free body diagrams for various types of force problems you're likely to come across. In later videos we'll actually work the problems through, but since this free body diagram is such a sticky topic for most physics students, I think it's wise to first concentrate ONLY on the diagrams, since if you don't get the hang of these, it's pretty much impossible to do the full force problems correctly.
What Is A “Free Body” Diagram?
You've probably wondered this. Most of the time when you do free body diagrams, it will be for problems similar to ones you've done before, so it basically becomes like a bad habit. But it will really impress your teacher if you know what's so free about those diagrams.
Basic Free Body Diagrams
This video shows you how to do free body diagrams for variations on the old "crate on a level surface" genre of force problem: a crate at rest, a crate being pushed, a crate being pulled by an angled rope, with and without friction. Also included: free body diagram for a crate suspended from the ceiling by angled ropes.
Ramp Problem Free Body Diagrams
This video covers free body diagrams for problems where an object is sliding up or down a ramp. I know what you're thinking: "Didn't we cover ramps before?" Sort of. And you should definitely watch that video. However, that was just kinematics; this one shows you how to draw the forces, including more practice with the X- and Y-components of gravity (mg).
Circular Motion Free Body Diagrams
This video covers how to do free body diagrams for objects being swung in a circle: a yo-yo and a car. The really key takeaway, in case you don't have time to watch, is to not put the "fictitious" centrifugal force on your free body diagram.
Multiple Object Free Body Diagrams
It seems like every book and class uses the same example where there are three boxes being pushed from one end. This video shows you how to divide the problem up into three separate free body diagrams so that you can carefully label and account for the forces on all three boxes.
Rope & Pulley Free Body Diagrams
This video shows you how to do the free body diagrams for two common problems involving two masses attached by a pulley: Atwood machines and inclined plane. The key to both is to set up your coordinate systems correctly, which unfortunately is confusing, but I've never found a better way to get these right.
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