From Mechanics

Revision as of 10:50, 26 June 2010 (edit) Ian (Talk | contribs) ← Previous diff		Revision as of 10:58, 26 June 2010 (edit) (undo) Ian (Talk | contribs) Next diff →
Line 47:		Line 47:
	| valign="top"|Moment (Nm)		| valign="top"|Moment (Nm)
	|-		|-
-	|5N at O	+	|5N at <math>O</math>
	| valign="top"| <math>5\times 0=0</math>		| valign="top"| <math>5\times 0=0</math>
	|-		|-

---

Revision as of 10:58, 26 June 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.

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 (Nm)
5N at \displaystyle 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}