bending moments in elasticity

[swaha]

regarding the equations of bending moments in elasticity suppose we have a beam of length l fixed at both ends. at a disttance x from a fixed end o there is point c. regarding equilibrium of the length x ie oc we ignore the reaction force acting at the end other than o. why?

if the beam is fixed rigidly at both ends then we take the reaction couples into account but if placed on knife edges it is not taken into account why?

can anybody suggest me with books on general properties of matter in university level, bachelor's honours. thank you in advance.

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please suggest good books that would be available in India.

[swaha]

why no reply?