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13. Moments

From Mechanics

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| valign="top"|Moment (Nm)
| valign="top"|Moment (Nm)
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|-
-
|5N at O
+
|5N at <math>O</math>
| valign="top"| <math>5\times 0=0</math>
| valign="top"| <math>5\times 0=0</math>
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|-

Revision as of 10:58, 26 June 2010

       Theory          Exercises      


Key Points

The moment of a 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.

The resultant moment about O is the sum of the moments about O.


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 0−9.6+0−3+6+2=−4.6 Nm
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