The physicist believed that because the two masses are connected, it would make sense to choose the coordinates based on the fact that the string length of | is constant. Is this reasoning flawed or does it make sense? Could it be beneficial? The physicist then concluded that the momentum associated with the center of the mass vector is conserved, and that they can move the Frame of reference to the center of mass. Is this correct? The diagram drawn represents m'l : m and m2 = M. Say there is a hollow can of radius R and length L with a small hole drilled through the center of the lid. A massless, taut string of length l is strung through the hole, and it connects two spiders. L>>l. One spider of mass m1 is confined to the outer/topside of the lid, while the other spider of mass m2 is confined to the inside walls of the can. A physicists approach to the question is to find the center of mass of the 2 spiders: The center of the 2 spiders is defined by: (x_c, y_c, z_c) (m1 + m2)x_c = m'l*x_'l + m2*x_2 (m1 + m2) _c = m1*y_1 + m2*y_2 (m1 + m2)z_c = m1*z_1 + m2*z_2 The separation of the 2 masses is defined by: x = x_2 x_1 y = y_2 - y_1 z = z_2 z_1