A reference frame where Newton’s second law is valid is called an inertial frame of reference. Force is absolute, so is mass(for sufficiently small speeds), so if a frame is to measure an acceleration $a_1=\frac{F}{m}$, given a frame $F_1$ measures acceleration $a$, there will always be such a f...

What this question is about (the 4 nomenclatures in short): Nielsen, M.A. and Chuang, I.L. state in their famous book (see http://dx.doi.org/10.1017/CBO9780511976667, p. 87 ff.) that there are 4 alternative definitions (or variants, nomenclatures) of projective measurements. 1)) Usually they are ...

When I look at pictures of the sun shield on the James Webb Space telescope (JWST), I see something that looks highly reflective (and hence must have a very low emissivity). My intuition tells me that this is no accident. On the NASA website (https://webb.nasa.gov/content/about/innovations/coatin...