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13. Moments

From Mechanics

Revision as of 10:29, 17 February 2010 by Ian (Talk | contribs)
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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 (Nm)
5N at O 50=0
8 N 81.2=9.6
7 N 70=0
6 N 60.5=3
5 N 51.2=6
4 N 40.5=2
Total Moment 09.6+03+6+2=4.6 Nm