Here's the excercise: A tensile test is carried out on a mild steel specimen of gauge length 40mm and cross-sectional area 100mm2. The results obtained for the specimen up to it's yield point are given below:
Load (kN) | 0 | 8 | 19 | 29 | 36 Extension(mm) | 0 | 0.015 | 0.038 | 0.060 | 0.072
I need to determine the gradient of the load / extension graph. When the data is plotted (in the book) on a graph it gives a straight line therefore the gradient should be any load (of the given values) divided by the corresponding extension gradient = load/(extension/1000) except e.g. the first one (8kN) gives 533*106 while the third one (19kN) gives 500*106.
Why and which one do I use for the calculations?