质量中心简称质心，指物质系统上被认为质量集中于此的一个假想点，质心的位置矢量是质点组中各个质点的位置矢量根据其对应质量加权平均之后的平均矢量。质心不一定要在有重力场的系统中才会有意义，而重心则否。值得注意的是，除非重力场是均匀的，否则同一物质系统的质心与重心通常不在同一假想点上。对于密度均匀、形状对称分布的物体，其质心位于其几何中心处。

在一个N维空间中的质量中心，坐标系计算公式为：

其中：

In physics, the center of mass of a distribution of mass in space is the unique point where the weighted relative position of the distributed mass sums to zero or the point where if a force is applied causes it to move in direction of force without rotation. The distribution of mass is balanced around the center of mass and the average of the weighted position coordinates of the distributed mass defines its coordinates. Calculations in mechanics are often simplified when formulated with respect to the center of mass.