sentences: ground is a kind of object & a skill point is a mean of preposition ->  a soccer ball and ground are kinds of objects  a soccer ball and ground are kinds of objects & when the form point is rolling, it is moving against the sky & friction occurs when two object 's surfaces move against each other -> friction will occur between the rolling soccer ball and the ground friction will occur between the rolling soccer ball and the ground  friction will occur between the rolling soccer ball and the ground & a soccer ball is a kind of object & slip vacuum the sail of an preposition to increase -> friction will cause the speed of the rolling soccer ball to decrease