I am having a hard time grasping contact curvature sums. Can someone give me a link to where there is a guide or a youtube video? or can someone help me here please. Here are the equations: 1/Rx = 1/rax + 1/rbx 1/Ry = 1/ray + 1/rby 1/R = 1/Rx + 1/Ry The question is this: The ball-outer race contact of a deep groove ball bearing has 10mm ball diameter, a 5.5 mm outer race concave groove radius and a 45 mm radius from the bearing axis to the bottom of the groove. The load on the ball is 500 N and the race and the ball are made of steel (E=206 GPa, v = 0.30). Apply Hertzian Contact Analysis to determine. (a) - Curvature Sum (Include diagrams to define contact geometry). From this I reckon it is talking about a rolling element bearing? I know how to do the rest of the questions but I really don't understand how to find the curvature sum. I have searched on google and youtube but all I find is reports and simulations, none of which actually explain anything.