How can forces be used to make objects move, change direction, or stop?
An unbalanced force (that is, a force where the net force is not zero) can cause a change in the speed or direction (or both) of an object. According to Newton's second law of motion, an applied force provides acceleration to an object. The law can be stated as:
F = m x a
where F is the applied force, m is the mass of the body, and a is its acceleration.
Depending on the magnitude and direction of the force, it can cause an object to move, stop or change direction. For example, in baseball a pitcher throws the ball with a certain speed towards the hitter, who hits it, thus applying a force to it. In the process, the ball changes direction and attains a certain speed (which is possibly different from its initial speed). It is also possible that a player manages to catch the ball, thereby stopping it completely. Riding a bicycle and speeding it up or down, turning it—all are examples of how forces can be used to change the speed and/or the direction of an object.
Hope this helps.