Why does a bob eventually come to rest?

Why does a bob eventually come to rest?

The body eventually come to rest cause of balanced force. It is seem in figure that an object is suspended with a thread. The force of attraction of earth on the object i.e. the weight of the object W is acting vertically downward. The tension of the thread T is acting vertically upward. Here the two forces are equal is magnitude but opposite in direction thus cancelling each other's action and producing a balanced condition.

Only the attractive force of the earth i.e. the force of gravity will act on the object if the thread is cut. Then the object will fall down with acceleration due to gravity. Here, the force of gravity or weight of the object is the unbalanced force. If the body is displaced slightly along one side, the tension of the thread T and the weight W will not be in a straight line. Then a resultant force will act on the body without creating balanced condition. Due to this, the body will oscillate. This is an example of unbalanced force.