In the following example, try to identify the number of times the velocity of the ball changes :
"A football player kicks a football to another player of his team who kicks the football towards the goal. The goalkeeper of the opposite team collects the football and kicks it towards a player of his own team.
Also identify the agent supplying the force in each case.

Explanation

First time, the velocity of the ball changes when the football player kick the football to another player of his team.
Second time, the velocity of the ball changes when another player of the same team kicks the ball towards the goal.
Third time, the velocity of the ball changes when the goalkeeper of the opposite team collects the ball Fourth time, the velocity of the ball changes when the goalkeeper kicks the ball towards the player of his own team.
Thus the velocity of the football change four times.
The agents applying the force are the different players.