sentences: sliding is a kind of movement & a rock is slided across the frozen pond ->  a rock is moving on the frozen pond  a rock is moving on the frozen pond & friction occurs when two objects move against each other & a rock is a kind of object & a frozen pond is a kind of object ->  friction will occur between the rock and the  frozen pond  friction will occur between the rock and the  frozen pond & a rock is a kind of object & friction causes the speed of an object to decrease -> friction will cause the speed of the rock to decrease