My son came with this "idea" to "exceed the speed of light" (he is still in school):
Imagine a disc of radius $R$ that is rotating so fast [with angular speed $\omega$ so large] that at a radius $r; r<R$ the [tangential] speed is the speed of light. Therefore the [tangential] speed at $R$ will be larger than the speed of light.
The blocks inside square brackets are mine as he was not even familiar with those specific concepts / notations.
I am an engineer, so my knowledge of physics is pretty much limited to mechanics, but I tried to explain to him the various reasons that would make his idea not possible. Besides explaining the impossibility of attaining such a high angular speed and the inability of any known material to withstand the forces caused by such high rotation, I tried to explain that it was not possible because the time will have to slow down and also because something has to happen to the mass of the outer portion of the disc so that the speed of light is not exceeded at $R$. I really do not feel comfortable with my explanations about time and mass, as I do not really understand how that works.
I would like to provide a more complete explanation to him as why is not possible (or what will happen), provided that the two big assumptions (a material with infinite resistance and the ability to create a very fast rotation) could hypothetically be done (if the second is not possible because of a physical constrain, I would appreciate your explanation for me as well!).
