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13. Moments

From Mechanics

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The resultant moment about <math>O</math> is the sum of the moments about <math>O</math>.
The resultant moment about <math>O</math> is the sum of the moments about <math>O</math>.
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'''[[Example 13.1]]'''
'''[[Example 13.1]]'''
[[Image:ex13.1whole.GIF]]
[[Image:ex13.1whole.GIF]]
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'''[[Example 13.2]]'''
'''[[Example 13.2]]'''

Revision as of 10:50, 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 09.6+03+6+2=4.6 Nm