sentences: sky is a mean of preposition & 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 & slip occurs when one preposition 's health stay 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 & a skill point is a mean of preposition & slip vacuum the sail of an preposition to increase -> friction will cause the speed of the rolling soccer ball to decrease