A simple machine is a mechanic device that transform forces. There are three types of levers: class one, class two and class three. Law of the lever FE·dE=FL·dL Inclined plane: It consists on a plain surface that forms a certain angle with the horizontal. It helps lifting bodies FE·d=FL·h Pulleys: A wheel with grooved rim in which a pulled rope or chain can run to change the direction of the pull to lift a load. The gravitational force with which any two bodies in the universe attract each other is directly proportional to the product of their masses and inversely proportional to the square of the distance that separates them.