 What is Tension?

The tension force is the force which is transmitted through a string, rope, cable or wire when it is pulled tight by forces acting from opposite ends. The tension force is directed along the length of the wire and pulls equally on the objects on the opposite ends of the wire.

Definition provided by Wikipedia The concept of tension in a string can be very difficult for beginning physics students to grasp. (Actually, it can be a very difficult concept for advanced physics students to grasp...)

If you hold a length of string taut between your hands, any force that you exert on one end of the string is transmitted through the string to the other hand. This "force" transmitted by the string is called the tension in the string. How does the tension in different parts of the string compare?

Suppose you hang a 5 Newton weight from a string, and hold the other end of the string in your hand. If the weight (and the string and your hand) is at rest, then the weight exerts a 5 Newton downward force on the lower end of the string, and you exert a 5 Newton upward force on the upper end of the string. What is the tension in the string? It is possible to build very plausible arguments that the tension in the string is 10 Newtons, or that it is 0 Newtons, or that it is 5 Newtons - but what is it, really, and why?

A key to the puzzle is the realization that tension is not force. A force always has a very definite direction - up, to the left, North, etc. The tension in a string or rope must follow the rope! The tension may have to extend around corners, over and under pulleys, etc. So, tension transmits a force through a string or rope, but tension is not force. Tension doesn't work exactly the way force does.

Definition and Picture provided by Batesville Community School Corporation  