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  • 0 posts edited
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Jan
25
comment Weightlessness in Satellites
@MartinJames: If the passenger is inside the satellite, the gravitational pulls from different parts of it will tend to cancel out even if he is not at its exact center. (Famously, they cancel out completely everywhere inside a uniform spherical shell). And even if they don't cancel out exactly due to irregularities of shape or density, the sum will not tend to pull him towards the center-of-mass.
Jan
21
revised How many neutrinos would it take to accelerate a 75kg human?
A few additional engineering numbers
Jan
21
revised How many neutrinos would it take to accelerate a 75kg human?
deleted 8 characters in body
Jan
21
revised How many neutrinos would it take to accelerate a 75kg human?
deleted 18 characters in body
Jan
21
revised How many neutrinos would it take to accelerate a 75kg human?
oops, the 12 came from nowhere
Jan
21
comment How many neutrinos would it take to accelerate a 75kg human?
Yes, I know $N_A$ is supposed to be dimensionless, but remembering it as "baryons per gram" seems to be easier for back-of-the-envelope calculations.
Jan
21
answered How many neutrinos would it take to accelerate a 75kg human?
Jan
21
comment How many neutrinos would it take to accelerate a 75kg human?
Relevant what-if, though it doesn't provide sufficient hard numbers to answer this one.
Jan
21
awarded  Guru
Jan
19
revised How am I able to stand up and walk down the aisle of a flying passenger jet?
added 9 characters in body
Jan
19
comment How am I able to stand up and walk down the aisle of a flying passenger jet?
@Aron: That parenthesis was meant to forestall unproductive discussion about how one even counts the chemical energy released by the muscles in the relativistic case. There's at least an argument that the chemical energy is subject to relativistic mass increase by a factor of $\gamma$, such that in the ground frame we should say the energy released by the passenger's muscles is $\gamma$ times what it is in the comoving frame.
Jan
18
revised How am I able to stand up and walk down the aisle of a flying passenger jet?
make it a bit harder to misunderstand
Jan
18
comment How am I able to stand up and walk down the aisle of a flying passenger jet?
@ejrb: The question here was "where does the passenger's increase in kinetic energy (as measured by the observer on ground) come from, given that it's not all supplied from chemical energy in his muscles?" My answer is that the same amount of energy is removed from the plane. Once the passenger stops (wrt the plane), this kinetic energy goes back into the plane.
Jan
18
awarded  Mortarboard
Jan
18
awarded  Good Answer
Jan
18
awarded  Nice Answer
Jan
17
revised How am I able to stand up and walk down the aisle of a flying passenger jet?
the factor of 1/2 gets eaten by the product rule when we differentiate ...
Jan
17
answered How am I able to stand up and walk down the aisle of a flying passenger jet?
Nov
4
comment How is hydrostatic pressure overcome when a star is formed?
Squares and cubes are not "exponential"!
Nov
1
comment Why is the energy stored in a driven oscillator equal to the product of friction dissipated power $P_\text{fr}$ & decay time $\tau$ at resonance?
How sure are you that only $e^{-1}$ of the energy is dissipated during time $\tau$? Usually "decay time $\tau$" would mean that $e^{-1}$ of the energy will be left after time $\tau$, so $1-e^{-1}$ of it -- which is most! -- will have been dissipated by then.