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# Week2_1 - ENGR210, Fall 2011 2.8 Force vector directed...

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ENGR210, Fall 2011 1 2.8 Force vector directed along a line Often in statics analyses, the direction of a force is specified by two points through which its line of action passes. In order to express the force vector, the unit vector along the line needs to be obtained. The unit vector, u , is determined as u = r / r where r is the position vector, r is the magnitude of r .

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ENGR210, Fall 2011 2 Then, the force vector is (Remember that “any vector (including a force vector) can be expressed as its unit vector (defining the direction) multiplied by the magnitude.”) Also, the unit vector of the position vector r and the unit vector of the force vector F are the same (i.e., u ).
ENGR210, Fall 2011 3 EXAMPLE 2.14

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ENGR210, Fall 2011 4 SOLUTION 1. Obtain the position vector r B. The coordinates for point A and B are (2, 0, 2) and (-2, 3.464, 3), respectively.
5 Therefore, r B = -4 i + 3.464 j + 1 k 2. Obtain the unit vector u B . 3. Compute

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## This note was uploaded on 10/16/2011 for the course ENGR 210 taught by Professor Ko during the Fall '08 term at Boise State.

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Week2_1 - ENGR210, Fall 2011 2.8 Force vector directed...

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