This read-only variable will return the y position of the instances center of mass. This is calculated automatically based on the density, inertia and mass of the instance as defined by the appropriate functions
Real (single precision floating point value, or undefined if the instance is not physics enabled)
xx = phy_com_x;
yy = phy_com_y;
The above code sets two variables to the x and y position of the instances center of mass.