When trying to turn a key into a lock, following is applied?
When two forces of equal magnitude are opposite in direction and acting along parallel straight lines, then they are said to form a couple. The perpendicular distance between the two forces forming a couple is called the arm of the couple.
Practical Application of a Couple:
To turn a car the driver applies a couple to the steering wheel
To wind the spring of an alarm clock, it is applied by the fingers
To open or close a water tap
To turn a key of a lock:- In order to turn a key in the keyhole of a lock, forces are applied by fingers. These forces form a couple.