What is a couple?

Hint: We need to understand the different types of forces and their applications. There are different kinds of forces depending on the method, direction, number, and nature of the application. A couple is such a type of force which has special properties.

Complete step-by-step solution
A force is the amount of energy spent on an object of mass ‘m’ per unit length with an acceleration ‘a’. From Newton's second law of motion. The force is defined as the rate of change of momentum with time.
\[\begin{align}
  & \dfrac{dp}{dt}=ma \\
 & \Rightarrow F=ma \\
\end{align}\]
There are different types of forces depending on the properties of the force applied. The thrust, tension, couple, normal reaction, weight are examples of a few forces in our daily life. The thrust is the force experienced by a floating body. The tension is the force experienced by a rope hung with a weight. The weight is the force due to the mass and the gravitational force. The normal reaction is the reaction or opposing force due to the weight.
We can discuss the couple in detail. The couple is a pair of equal and opposite forces separated by a distance. We know that according to Newton's third law of motion. Two equal and opposite forces will result in the mutual cancellation of the forces. But the couple forces are separated by a distance, which becomes an inevitable force required in our daily life.

The couple enables the rotational motion of a substance. The opening of bottles and other containers is possible by the application of couple of forces.

Note: We use the couple forces almost always in our day-to-day life. The forces to cause a cap of a bottle to open required balance from both sides for opening as a single force will not allow the opening on the cap as effectively as we do.