Hello, I am currently studying how to find the centroid of shapes. And I understand that to find the location of the centroid, we must analyze the distribution of the mass over the x and y axis (i.e calculating Qx and Qy). However what baffles me is that, given an L shaped beam, the centroid does not necessary need to lie on the mass itself? I thought the centroid was the location where all the mass is concentrated. How does it make sense that , say the force of gravity, acts outside the shape? Thank you !