what is couple?what is physical meaning of torque and how to apply it in physical sense

Dear Krish Mishra,

A Couple is a system of forces with a resultant (a.k.a. net, or sum) moment but no resultant force.^[1]Another term for a couple is a pure moment. Its effect is to create rotation without translation, or more generally without any acceleration of the centre of mass.

The resultant moment of a couple is called a torque.

Simple couple

The simplest kind of couple consists of two equal and opposite forces whose lines of action do not coincide. This is called a "simple couple".^[1] The forces have a turning effect or moment called a torqueabout an axis which is normal to the plane of the forces. The SI unit for the torque of the couple isnewton metre.

If the two forces are F and −F, then the magnitude of the torque is given by the following formula:

where

τ is the torque

F is the magnitude of one of the forces

d is the perpendicular distance between the forces, sometimes called the arm of the couple

The magnitude of the torque is always equal to Fd, with the direction of the torque given by the unit vector , which is perpendicular to the plane containing the two forces. When d is taken as a vector between the points of action of the forces, then the couple is the cross productof d and F.

The direction of the torque comes from the right hand rule, which is a mathematical convention based on the fact that most humans are right handed.  Torque doesn't "stick out" in that direction.  You could do all your math with the proper signs using a left-handed coordinate system and do physics just fine.  It doesn't mean anything physically, it's a mathematical tool we use to keep signs and directions consistent. 

             

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Dear Krish Mishra,

Couple,  in mechanics, pair of equal parallel forces that are opposite in direction. The only effect of a couple is to produce or prevent the turning of a body. The turning effect, or moment, of a couple is measured by the product of the magnitude of either force and the perpendicular distance between the action lines of the forces.

The steering wheel of an automobile is turned by hand forces that constitute a couple, and a screwdriver is twisted by the equivalent of a couple. A wrench, on the other hand, is actuated by a force applied at one end only, and, in addition to the turning moment, it creates an unbalanced force on the element being tightened.

Torque is nothing but a twisting force that tends to cause rotation of something !!

Hope you understood now..

All the Best & Good Luck !!

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