सुरक्षा गुणांक (Factor of safety) को गणितीय रूप से किसके बराबर परिभाषित किया गया है?

When a bar of length l and uniform cross-section is rigidly fixed at the upper end and hangs freely, the total elongation produced in the bar due to its own weight is given by (where w = weight per unit volume and E = Modulus of Elasticity):

The hoop stress set up in a thin cylinder subjected to internal fluid pressure is: