Magnets can attract or repel other materials and have useful applications like holding items on refrigerators. The six simple machines - lever, screw, pulley, wheel and axle, inclined plane, and wedge - help do work and add force to move objects. A lever consists of a bar and fulcrum and can help lift weights with less effort. Matter exists as solids, liquids, or gases and can change forms through processes like melting, freezing, condensation, and evaporation.