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-	Find the moment of each force shown below about the point O.
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-	Solution
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-	<math>20\times 0.8=16</math>
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-	Moment is -16 Nm
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-	<math>12\times 1.2=14.4</math>
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-	Moment is 14.4 Nm
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-	Find the moment of each force shown below about the point O.	+	Example 13.3
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-	<math>40\times 3\sin 60{}^\circ =104</math>
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-	<math>100\times 2\sin 20{}^\circ =68.4</math>
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-	Moment is 104 Nm (to 3 sf) Moment is 68.4 Nm (to 3 sf)
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-	Example 13.3
	For the rectangular lamina shown below, find the total moment of the forces acting, about the corner marked O.		For the rectangular lamina shown below, find the total moment of the forces acting, about the corner marked O.
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	Solution		Solution

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Revision as of 19:22, 17 September 2009

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.

\displaystyle \text{Moment }=Fd

\displaystyle \text{Moment }=Fd\sin \theta

Clockwise moments are negative. Anti-clockwise moments are positive.

Example 13.1

Example 13.2

Example 13.3

For the rectangular lamina shown below, find the total moment of the forces acting, about the corner marked O.

Solution

Force Moment 5N at O \displaystyle 5\times 0=0

8 N \displaystyle -8\times 1.2=-9.6

7 N \displaystyle 7\times 0=0

6 N \displaystyle -6\times 0.5=-3

5 N \displaystyle 5\times 1.2=6

4 N \displaystyle 4\times 0.5=2

Total Moment \displaystyle 0-9.6+0-3+6+2=-4.6\text{ Nm}