# Why do we need to take distance of center gravity of a distributed load to a point in order to calculate moment?

From the picture above, in order to calculate the moment of load acting on the beam we take moment $M=\frac{W}{L}×L×\frac{L}{2}$.

Why can't we calculate the moment as $M=\frac{W}{L}×L×L$?

Why do we need to take the distance from center of gravity to a point as the distance?

However, beware that the moment you gave in your question is valid for a cantilever beam with uniform load, and that's not what is in your drawing shows. Your drawing shows a simple supported beam, that is, supported at both ends. The maximum moment in a simple supported beam is $M=\frac{W}{L}\times\frac{L^2}{8}$.