Im confused on what the significance of exact differentials are in physics, specifically in thermodynamics. In my book posted here it talks about how by requiring that $dU$ be exact it leads to equation (1.4). So my questions are, How and why do we have the requirement that $dU$ be exact? What do...

There is a box on the surface of earth. The earth exerts a force to the box (black arrow). The box exerts a reaction force to the earth(brown arrow). But this reaction force is exerted to the earth not the box, so where is the normal force? If the reaction is the normal force then why they put th...

The way I understand it, temperature is the average kinetic energy of the particles of a system. However, kinetic energy depends on the velocity of the particles, which is relative. If a cup of coffee were traveling at 99% the speed of light relative to an observer, its particles would have much ...

In the Standard Model, with the introduction of the CKM matrix, we have that quark mixing between different generations is possible via a charged current (W boson). My question is if this also implies that a given quark can change flavour (oscillate), auto-interacting with itself via a W boson. F...

If a body $A$ exerts a force over body $B$, $B$ exerts a reaction force over $A$. Is there an explanation of why this happens?