"'Rolling Along' explores the benefits and uses of the wheel and axle. RobbO and RobbEE build a cart to make it easier to move a heavy load, and learn how the wheel and axle are also used for lifting and turning."--Provided by publisher.
'Pulling Up' explores the benefits and uses of the pulley. RobbO and RobbEE need to build a pulley to move the engine in a car. They find lots of other uses for a pulley too.
