For two masses x and y, its acceleration equals x minus y divided by x plus y times the acceleration due to  [*] gravity. The unequal gravitational forces acting individually 
For two masses x and y, its acceleration equals x minus y divided by x plus y times the acceleration due to  [*] gravity. The unequal gravitational forces acting individually on the two masses, combined with the requirement of structural continuity, yield a constant acceleration. Named for a reverend—for 10  points—name this device in which two unequal masses are attached to a flexible, ideally massless string passing over an ideally frictionless, massless pulley.
For two masses x and y, its acceleration equals x minus y divided by x plus y times the acceleration due to  [*] gravity.
Atwood machine