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 DrDanger Feb19-09 02:01 PM

Free Body Diagrams

Hey everyone hows it going? I am not sure if this is the right place to be posting this question, but hopefully it is. My names Shawn and I am a senior in high school. I currently have AP calculus and gen physics, and I plan on taking the AP calculus test (ab) and hopefully the physics AP test, but I am not sure which one to take? Has anyone here taken either? I have borrowed an AP physics book ( Princeton review) and have been teaching it to myself. I think I am getting the concepts and everything but get lost a little here and there. Right now I am reading about Rotational Motion, but I am lost on drawing a Free body diagram. I can draw them right most of the time, but when it comes to putting it into the equation Fnet=ma thats where i get lost..So what should i be asking myself before i attempt to put it into the equation?. So any help on that would be greatly appreciated! Also i am having a tough time on the free response questions after every chapter, i can do the multiple choice questions with a little effort,but get stumped at the free response. After I see it done i always say "oh why didn't i think of that?". I am just having a hard time plugging equations into other equations into other equations etc to find what i need. Also one last thing, i learn best by doing problems so if you know of any good sites with problems AND ANSWERS with it worked out that would be awesome! Thanks for taking the time to help me!

 Dr.D Feb19-09 03:15 PM

Re: Free Body Diagrams

FBDs are not really complicated if you remember to include all of the REAL forces that act on the body, and don't include any non-forces, such as mass*acceleration terms. Real forces include things like gravity forces, friction forces, contact (normal) forces between bodies, applied forces, and pressure forces such as buoyancy. These are the terms that go into the sum of forces.

The other side of Newton's second law, the mass*acceleration term requires that you have a proper understanding of how to express the acceleration in the coordinate system you are using.

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