A new Atwood's machine attachment has been designed in which one side of the system consists of a drum around which the string is wrapped so that the drum rotates as it falls. The other side of the system consists of a falling body, whose mass can be varied. Two sparktimer records are taken, one for the drum, and one for the falling body. Data taken are used to verify the law of motion of the mass center and the law of motion about the mass center.