sentences: a ramp is a kind of object & a block is a kind of object ->  a block and a ramp are kinds of objects  a block and a ramp are kinds of objects & sliding is a kind of moving & a block is sliding down a ramp & friction occurs when two object 's surfaces move against each other ->  friction occurs between the block and the ramp  friction occurs between the block and the ramp & friction causes the speed of an object to decrease & a block is a kind of object -> friction causes the speed of the block to decrease