13. Moments
From Mechanics
(Difference between revisions)
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== '''Key Points''' == | == '''Key Points''' == | ||
| - | The moment of | + | 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. | ||
| - | + | 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 \displaystyle O is the product of the force and the perpendicular distance to the line of action of the force from \displaystyle O.
\displaystyle \text{Moment }=Fd
\displaystyle \text{Moment }=Fd\sin \theta
Clockwise moments are negative.
Anti-clockwise moments are positive.
The resultant moment about \displaystyle O is the sum of the moments about \displaystyle O.
For the rectangular lamina shown below, find the total moment of the forces acting, about the corner marked O.
Solution
| Force | Moment (Nm) |
| 5N at O | \displaystyle 5\times 0=0 |
| 8 N | \displaystyle -8\times 1\textrm{.}2=-9\textrm{.}6 |
| 7 N | \displaystyle 7\times 0=0 |
| 6 N | \displaystyle -6\times 0\textrm{.}5=-3 |
| 5 N | \displaystyle 5\times 1\textrm{.}2=6 |
| 4 N | \displaystyle 4\times 0\textrm{.}5=2 |
| Total Moment | \displaystyle 0-9\textrm{.}6+0-3+6+2=-4\textrm{.}6\text{ Nm} |
