Could someone please help me to understand the difference between the concepts of Weak Isospin, Chirality and Helicity. In particular, I have the following questions to which I was unable to find answers so far: 1. Since both spin direction and momentum are vectors, would not their apparent direction depend on the observer's reference frame and would not the same particle appear to have different Chirality to two different observers? E.g. Earth has both spin and momentum, but would not those vectors appear to have the same direction to an observer on Mars, while appearing to have different direction to an observer on Venus? 2. Would not knowing the direction of a particle's spin imply measuring its orientation in space? If so, would not determining directions of both its spin and momentum violate Heisenberg's Uncertainty Principle? 3. How comes that all common quarks and leptons are considered "left-handed" (i.e. have the same chirality), but up-type quarks and neutrino have positive weak isospin, while this value is negative for down-type quarks and e-/μ-/τ-?