and a massless string) in textbooks to solve the dynamics problem of Atwood machine. The dynamical methods are

used to describe the motion of Atwood machine with a massive string. The effects on the system motion caused by

the mass of the pulley，the mass of the massive string and the initial position of the weight are analyzed. Furthermore，

the difference between the ideal model described in the text book and the motion of the Atwood machine under

the real conditions is discussed.