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13. Moments

From Mechanics

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== '''Key Points''' ==
== '''Key Points''' ==
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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.
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The moment of a force about the point <math>O</math> is the product of the force and the perpendicular distance to the line of action of the force from <math>O</math>.
[[Image:T13.1.GIF]]
[[Image:T13.1.GIF]]
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<math>\text{Moment }=Fd</math>
<math>\text{Moment }=Fd</math>
[[Image:T13.2.GIF]]
[[Image:T13.2.GIF]]
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<math>\text{Moment }=Fd\sin \theta </math>
<math>\text{Moment }=Fd\sin \theta </math>
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Anti-clockwise moments are positive.
Anti-clockwise moments are positive.
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The resultant moment about <math>O</math> is the sum of the moments about <math>O</math>.
'''[[Example 13.1]]'''
'''[[Example 13.1]]'''

Revision as of 13:42, 8 March 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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