Key Concepts to Remember while Solving Problem

Key Concepts to Remember while Solving Problem

1. To find moment of force about a point, either find the perpendicular distance or resolve the force into two mutually perpendicular components for which perpendicular distances are known.

2. To produce maximum moment with a given force to produce some given moment with minimum force, force must be applied at maximum distance from the point about which moment is taken and the force must be applied perpendicular to the line joining the point of application of force to the point about which moment is taken.

3. The resultant force for a couple is zero. Couple has only resultant moment.

4. To find resultant of non-concurrent force system, find resultant force in magnitude and direction using.

If R = 0, resultant can be a moment which can be obtained by taking moment about any point in the plane.

If R ≠ 0, the line of action of resultant can be obtained using Varignon's theorem.

5. Two force systems are equivalent or equipollent when they have the same magnitude, direction and line of action of resultant force. This can be used to replace a force by two parallel or two non-parallel forces acting at different points. 

6. If moment of force has same sense of rotation about two points, the line of action of that force must lie outside the two points. For opposite sense of rotation, the line of action must be somewhere between the two points.

7. Moment of force is larger about that point from which the perpendicular distance is larger.

8. If line of action of force passes through the point about which moment is taken, the moment of force is zero.