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13. Moments

From Mechanics

Revision as of 11:09, 18 September 2009 by Ian (Talk | contribs)
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       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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