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Nov
16
comment Physical meaning of the angular momentum
@DavidHammen: but just choosing a different point of reference will not affect linear momentum - in contrast to angular momentum, you need to introduce relative motion for that to happen; that aside, your point is of course a valid one
Nov
15
revised Is a photon really massless?
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Nov
15
comment Is a photon really massless?
@kstb: a photon indeed has no rest mass; if you chose to do so (I do not), you could assign a relativistic mass that depends on the photon's frequency
Nov
15
comment Is a photon really massless?
@kstb: $E=mc^2$ is incomplete if $m$ denotes rest mass; the general formula is $E^2=m^2c^4+p^2c^2$ with special cases $E=\gamma mc^2$ for massive and $E=h\nu$ for massless particles; in principle, you could assign a 'relativistic mass' of $m_r=h\nu/c^2$ to photons, but personally, I wouldn't recommend doing so
Nov
15
revised Is a photon really massless?
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Nov
15
answered Is a photon really massless?
Nov
3
comment What is a rocket engine thrusting against in space?
the rocket doesn't push against empty space, but against its exhaust gas
Oct
28
awarded  Enlightened
Oct
19
answered How can one derive Schrödinger equation?
Oct
19
comment How quickly does gravity extend from created mass?
@LDC3: it's a theoretical prediction consistent with the orbital decay of binary pulsars, most famously PSR 1913+16 (cf Nobel price 1993, arXiv:1011.0718)
Oct
19
revised Reconciling Units in Classical System Analogies: Why Does Torque Have Units of Energy?
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Oct
19
answered How quickly does gravity extend from created mass?
Oct
19
revised Reconciling Units in Classical System Analogies: Why Does Torque Have Units of Energy?
added 148 characters in body
Oct
19
revised Reconciling Units in Classical System Analogies: Why Does Torque Have Units of Energy?
added 148 characters in body
Oct
19
answered Reconciling Units in Classical System Analogies: Why Does Torque Have Units of Energy?
Oct
16
comment Are Lockheed Martin nuclear fusion claims realistic?
see also en.wikipedia.org/wiki/Magnetic_mirror
Oct
16
revised What is divergence?
make answer easier to digest
Oct
16
revised What is divergence?
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Oct
16
answered What is divergence?
Oct
16
comment What is divergence?
The divergence of a vector field is the infinitesimal relative change in volume when transporting a volume element along its flow. The abstract definition in terms of Lie derivative and volume form is quite intuitive here.