10. Moment of Force II Types of Moments II Laws of Moments II Couple II Characteristic of couple II

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Moment of a Force :-
It is the turning effect produced by a force on the body on which it acts. The moment of a force is equal to the product of the force and the perpendicular distance of the point about which the moment is required.
Types of moment's
1. Clockwise moment
2.Anticlockwise moment
Applications of moments:
1. Position of resultant force
2. Finding support reactions
3. Balance
4. Lever safety value
5. Lever
6. Steel yard
Law of moments:
It states that If a body is an rotational equilibrium under the action of a number of forces, then the sum of the clockwise moment of the forces about any point is equal to the anti clockwise moments of the forces about the same point.
Sum of clockwise moments = Sum of anticlockwise moment
Varignon's principle of moments:-
It states that “If a number of coplanar forces are acting simultaneously on a particle, then the algebric sum of the moments of all the forces about any point is equal to the moment of their resultant force about same point”.
Couple:-
A pair of two equal & unlike parallel forces (i.e. forces equal in magnitude, parallel to each other & acting in opposite directions) is known as a couple. OR
Two parallel forces equal in magnitude but opposite in direction & separated by a finite distance.
Examples of a couple :-
1. Opening or closing a water tap
2. Unscrewing the cap of any bottle
3. Locking or unlocking of a lock with key
4. Forces applied to the handle of a screw
Characteristics of Couples:-
1. The algebric sum of the forces constituting the couple is zero.
2. The algebric sum of the moments of the forces, constituting couple about any point is the same and equal to the moment of the couple
A couple cannot be balanced by a single force. But it can be balanced only by a couple.
Any no. of coplanar couples can be reduced to a resultant single couple, whose magnitude will be equal to algebric sum of the moments of all the components couples.
Arm of couple:-
The perpendicular distance between the lines of action of the two equal & opposite parallel forces is known as arm of the couple.
Moment couple:-
The moment of a couple is the product of the force and the arm of couple.
moment of couple = P x a
Where P- magnitude of force
a- arm of couple