An equation for the acceleration can be derived by analyzing forces. Assuming a massless, inextensible string and an ideal massless pulley, the only forces to consider are: tension force (T), and the weight of the two masses (W 1 and W 2). To find an acceleration, consider the forces affecting each individual mass. Using Newton's second law (with a sign convention of m 1 > m 2 ) derive a system of equations for the acceleration (a).