Force, Moments , and Couple Study Materials
Force
Force is an agent which changes or tends to change the state of rest or of uniform motion of a body upon which it acts. A Force represents the action of one body on another. Force is a vector quantity (i.e, Force has got both magnitude and direction)
Characteristics of a force:
A Force is characterized by
- Magnitude
- Line of action
- Direction
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Moments of a Force:
Moment of a force about a point is defined as the product of the force and the perpendicular distance of the line of action of the force from that point.
In the above figure, F is a downward force applied at ‘A’ and r is the perpendicular distance of the line of action of the force from the point O.
The moment (μ) of the force F about ‘O’ is given by
μo= F x r (i.e. Force x Perpendicular distance)
Downward force applied at A1 will have a tendency to rotate OA about the point ‘O’. Hence moment may also be defined as the turning effect produced by a force.
Moment is classified into two types.
- Clockwise moment
- Anticlockwise moment
Couple:
Two forces F and –F having the same magnitude, parallel lines of action and opposite sense are said to form a couple.
Sum of the moment of couple forces about any point is same in magnitude and nature.
Moment of a couple = Force x arm of the couple.
M = F x a
Difference between Moment and Couple :
The couple is a pure turning effect which may be moved anywhere in its own plane or into a parallel plane without change of its effect on the body, but the moment of a force must include a description of the reference axis about which the moment is taken.
Types of couple :
- Clockwise couple
- Anticlockwise couple
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