Fabio you're not listening to me , the general relativity says that spacetime is torsionless it means that the spacetime has zero skew, imagine a rotating pendulum it has the same properties as a regular pendulum but now the rotational inertia and the elasticity of the string replaces the mass, this rotating pendulum can't exist in spacetime because the spacetime doesn't twist like that however you can still use the linear approach of SR in rotating matter, imagine the electron position annihilation which gives two photons, this means that these particles have the same structure, the electron has charge of -1 , the positron of +1 why is that? the only explanation is that their relative angle is fixed, it means that through natural selection certain matter evolved into what is the electron and proton like complex organism evolved, it also means there are other particles which we haven't explored and this may be true since there are 100s of particles unidentified yet in collision experiments, now the question is what is mass and what is stored in spacetime as mass , there is the rest mass and the relativistic mass or longitudinal mass but there's also transverse mass so in total there are 3 masses and if you count the inertial mass which is not always the same as rest mass there are 4 masses but mass is energy or better yet energy is mass, what is stored in spacetime is energy but like cogs in a clock these don't spin faster on their own, the only way to get the energy out is through fusion or fission it means that the matter waves of the nucleons drop to lower energy states, the matter waves of the nucleons have acquired their energy from creation or the big bang, this is the only spacetime energy you can harvest possibly, the elasticity of spacetime doesn't allow you to store more energy than what you put out, also in experiments if you use wires then the velocity of charges is ultra low some m/s because the wire has billions of atoms as charge carriers the same field creates all fields but with low speed the other fields are almost zero, everyone still things of induction of coils but there is also induction of charges which is what induction of coils is the curvature of the coil adds to induction which is why everyone thinks of induction of curved surfaces, if you do FEMM simulations which uses the 3 maxwell equations of EM but for infinitesimal regions you can get solutions which don't agree with what you get if you do them by hand so to finish with this instead of thinking about wires think about what each charge is doing then add all the fields together, the superposition principle applies to all fields so a cancelling magnetic field is never cancelled