Difference between moment and couple

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Moment and couple are two important concepts found in mechanics. They both terms describe the effect and cause of rotation in the system of forces, particle systems, and rigid bodies too. 

What is a moment of a force?


The turning effect produced by a force applied to a rotational system or on the body at a distance from the axis of rotation is called the moment of force. The moment of a force is the product of the force and the perpendicular distance of the point, about which the moment is required and the line of action of the force.

What is a couple OR moment of a couple? 


In mechanics, a couple refers to two equal and opposite forces, whose line of action is different from a couple. The couple also called a force couple or pure moment. 

Points of difference between moment and couple are discussed below. So let us check out some key differences between them to know more about it. 

Difference between moment and couple:

  • The moment is the measure of the turning effect of a force about the point whereas a couple is equal and opposite forces acting with two different but parallel lines of action. 
  • The moment is dependent on the distance from the pivot and the force while the couple is a net effect of the two moments of the forces. 
  • The couple is independent of the location of the point considered while the moment is dependent on the location of the point. 
  • The moment is produced by a single force and the couple produced by two forces. 
  • The moment may have a resultant force but in case of a couple resultant force is zero. 

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