Coulomb's Law- Why the Coulomb's law is valid only for point and static charges? Why the coulomb's law is valid only for point and static charges?
Is there is any definite reason?
 A: It is really valid for distributions too, but you need to use the integral form.
To see why it is only "valid" for point charges, take a look at the equation (for a point particle, the one you have probably been looking at). It refers to the distance from the source, which is only defined for a point, not a distribution.
It is however not valid for moving charges. This is because the information about the position of the charge (the field caused by the charge) can only travel at the speed of light. See this link if you're interested in moving charges.
A: Coulomb's law does not apply to two charged bodies of finite sizes, say two charged spheres. It is because, the distribution of charge does not remain uniform, when the two bodies are bought together.$_1$  

Credits: $_1$ Modern's abc of Physics-Satish K Gupta, 23rd edition, pg.14.
A: The "traditional" form of Coulomb's law, explicitly the force between two point charges. To establish a similar relationship, you can use the integral form for a continuous charge distribution and calculate the field strength at a given point.
In the case of moving charges, we are in presence of a current, which generates magnetic effects that in turn exert force on moving charges, therefore, no longer can consider only the electrostatic force.
A: Say you have two point charges separated at some distance in a particular medium. You can simply use the equation and calculate the force between them because you know here the exact distance between two exact point charges.
Now, take a large scale body having so many electrons embedded in it, and say, the charge is $-15\ \mu C$. Now, take an electron, can you calculate the force between the body and the electron using your simple Coulomb's equation? Simple No, because you don't know here the exact distance between the electron and that $-15\ \mu C$ charge. If it were $-1.6 \times 10^{-19} \ C$, you can easily calculate that(electron-electron force). Hence, in distribution of charges, we can't apply Coulomb's law. If a charge is uniformly distributed over a line, a surface or a volume, you can easily calculate the force due to it on a point charge using integration.
I hope this clears your doubt!
A: If apply in moving charge then no. Of forces act on them so we can't calculate position of charges but in case of static it is possible so it applicable only for point charge or static
