Force can change a number of things about an object. These include:
- both speed and direction
Note that unbalanced forces can do any of these, since the net total of forces is not zero. In the case of balanced forces, nothing about the object will change.
When we apply a force to an object, we can change the direction of motion of an object. For example, a tennis player receives the ball from the other player, applies force on it (through his racquet) and returns it, thereby changing the ball's direction. We can also speed up an object by applying the force in the direction of motion. Imagine teaching a 4-year old how to ride a bicycle. We give the initial force to propel the bicycle in addition to the force the kid is applying on it, thereby speeding it up. We also stop the bicycle by applying force in the other direction, thereby reducing its speed, when needed. We can change both speed and direction at the same time by the proper use of force. Imagine slowing down your bicycle while taking a turn. The shape of an object can also be changed by applying force on it. An example is modeling clay, which can be given different shapes by the application of force on it.
Hope this helps.