Processing Math: Done

From Mechanics

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.

Moment =Fd

Moment =Fdsin

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

Example 11.1 Find the moment of each force shown below about the point O.

(a) (b)

Solution (a) (b)

2008=16

1212=144

Moment is -16 Nm Moment is 14.4 Nm

Example 13.2 Find the moment of each force shown below about the point O. (a) (b)

Solution (a) (b)

403sin60=104

1002sin20=684

Moment is 104 Nm (to 3 sf) Moment is 68.4 Nm (to 3 sf)

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 50=0

8 N −812=−96

7 N 70=0

6 N −605=−3

5 N 512=6

4 N 405=2

Total Moment 0−96+0−3+6+2=−46 Nm