Consider a bowling ball (or some other heavy object that moves with little resistance). If you want the ball to move, you have to exert a force on it in the direction you want it to move. If you want the moving ball to turn, you have to exert a force on it toward the side you want it to turn toward. If you want the ball to stop moving, you have to exert a force opposite to its velocity.  To change the motion of the bowling ball, you will probably apply a force by using your hands or feet or some object you push against the ball. There are other kinds of forces, however. The earth, for example, can alter the ball's motion through the invisible action-at-a-distance of [gravity], often represented as a gravitational field acting on the body at the site of the body.