质量中心简称质心，指一个物体的质量被认为集中于一个假想点。与重心不同的是，质心不一定要在重力场的系统中。要特别指出，除非重力场是均匀的，否则同一物体的重心和质心是不重合的。

The center of mass,  means that the mass of an object is thought to be concentrated at an imaginary point.Unlike the center of mass, the center of mass does not have to be in a system of gravitational fields.In particular, the center of mass and the center of mass of the same object do not coincide unless the gravitational field is uniform.