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13. Moments

From Mechanics

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Example 13.1
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'''[[Example 13.1]]'''
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[[Image:ex13.1whole.GIF]]
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Example 13.2
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'''[[Example 13.2]]'''
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Example 13.3
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'''[[Example 13.3]]'''
For the rectangular lamina shown below, find the total moment of the forces acting, about the corner marked O.
For the rectangular lamina shown below, find the total moment of the forces acting, about the corner marked O.
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Solution
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'''Solution'''
{| width="100%" cellspacing="10px" align="center"
{| width="100%" cellspacing="10px" align="center"

Revision as of 11:14, 18 September 2009

       Theory          Exercises      


Key Points

The moment of the force about the point O is the product of the force and the perpendicular distance to the line of action of the force from O.


Image:T13.1.GIF

Moment =Fd


Image:T13.2.GIF

Moment =Fdsin


Clockwise moments are negative. Anti-clockwise moments are positive.


Example 13.1

Image:ex13.1whole.GIF



Example 13.2

Image:ex13.2.GIF


Example 13.3

For the rectangular lamina shown below, find the total moment of the forces acting, about the corner marked O.


Image:ex13.3.GIF

Solution

Force Moment
5N at O 50=0
8 N −812=−96
7 N 70=0
6 N −605=−3
5 N 512=6
4 N 405=2
Total Moment 0−96+0−3+6+2=−46 Nm
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