MasteringPhysics-ch 4

# MasteringPhysics-ch 4 - MasteringPhysics Assignment Print...

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MasteringPhysics: Assignment Print View http://session.masteringphysics.com/myct/assignmentPrint?assignm. .. 1 of 28 10/20/07 10:59 PM [ Print View ] physics 2211 MP04: Chapter 4 Due at 5:30pm on Monday, October 1, 2007 View Grading Details Free-Body Diagrams: Introduction Learning Goal: To learn to draw free-body diagrams for various real-life situations. Imagine that you are given a description of a real-life situation and are asked to analyze the motion of the objects involved. Frequently, that analysis would involve finding the acceleration of the objects. That, in turn, requires that you find the net force . To find the net force, you must first identify all of the forces involved and then add them as vectors. Such a procedure is not always trivial. It is helpful to replace the sketch of the situation by the drawing of the object (represented as a particle) and all the forces applied to it. Such a drawing is called a free-body diagram . This problem will walk you through several examples of free-body diagrams and will demonstrate some of the possible pitfalls. Here is the general strategy for drawing free-body diagrams: Identify the object of interest. This may not always be easy: A sketch of the situation may contain many objects, each of which has a different set of forces acting on it. Including forces acting on different objects in the same diagram will lead to confusion and a wrong solution. Draw the object as a dot. Draw and clearly label all the forces acting on the object of interest. The forces should be shown as vectors originating from the dot representing the object of interest. There are two possible difficulites here: omitting some forces and drawing the forces that either don't exist at all or are applied to other objects. To avoid these two pitfalls, remember that every force must be applied to the object of interest by some other object--or, as some like to say, "every force must have a source." Once all of the forces are drawn, draw the coordinate system. The origin should coincide with the dot representing the object of interest and the axes should be chosen so that the subsequent calculations of vector components of the forces will be relatively simple. That is, as many forces as possible must be either parallel or perpendicular to one of the axes. It should come as good news that, even though real life can present us with a wide variety of situations, we will be mostly dealing with a very small number of forces. Here are the principal ones of interest: Weight, or the force due to gravity. Weight acts on every object and is directed straight down unless we are considering a problem involving the nonflat earth (e.g., satellites). Normal force.

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MasteringPhysics-ch 4 - MasteringPhysics Assignment Print...

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