If the metric is a (0,2)-tensor then it transforms twice covariently under a basis transformation, but in special relativity the metric seems to be defined globally as: $$\eta_{\mu\nu}=\begin{pmatrix}-1 && 0 && 0 && 0 \\ 0 && 1 && 0 && 0 \\ 0 && 0 &&1&&0\\0&&0&&0&&1\end{pmatrix}$$ in most texts...

From this source, on average a rubber tyre loses $2$ atoms thickness per revolution due to the friction with the road. Do these atoms/molecules that were peeled off the tyre get absorbed by the road? Then would the road increase in thickness due to this? If so, why doesn't the road lose it's ...

I have a bit misconception about weight which I want to clarify. The air pressure is explained as the weight of the air column above our head acting per unit area. But since air is not continuous how can the weight of all the air molecules (above our head) be acting on our head. I mean we would...

we can define cross products mathematically like if we take two vectors then we can find another vector with certain properties but why do we use it in physics, if we consider a hypothetical physical quantity like a force which is equal to cross product of certain vectors (example force on a char...