Hagen von Eitzen

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111 reputation
3
bio website von-eitzen.de/math/tntrep.xml
location Bonn, Germany
age 48
visits member for 1 year, 11 months
seen yesterday

I did study math and had a knack for it, but I am sooo out of that business now ...


Aug
10
comment Why does the Sun's (or other stars') nuclear reaction not use up all its “fuel” immediately?
I like this answer more than the other more technical ones because it focuses on the aspect of equilibrum. For example, the "velocity distribution of nuclei" is such that only the top speed nuclei can react because (simplified) a larger fraction of reactive nuclei would lead to more reaction, would lead expansion against the gravitational pressure, would lead to lower density, would lead to less reacton
Aug
10
comment Why does the Sun's (or other stars') nuclear reaction not use up all its “fuel” immediately?
In a way, the Sun is faster than a nuclear bomb. It emits the $E=mc^2$ equivalent of four million tons of matter per second, whereas a nuclear bomb converts only a tiny fraction of its mass (when we talk about a four megaton bomb, this refers to the chemical energy contained in 4 million tons of TNT).
Jul
10
comment Special relativity and electromagnets
The moving electrinns are cordially invited to be denser in the lab frame, but that would create forces driving them apart, thus "fleeing" from the wire along the current until neutrality is attained. Of course, with an infinite wire we may run into different theoretical trouble (we couldn't get the current running at the full length at once, we would have waves propagating, ...)
Apr
5
comment Why is jumping into water from high altitude fatal?
Even a "graceful diuver" entering vertically, toes ahead, will suffer from the following: The toes start accelerating with $770g$ about $0.01s$ before the head enters; per $\frac12at^2$ they have moved up (relatively) by $\approx 37cm$ then and move with $\approx 75m/s$ towards the head. That doesn't sound healthy.
Feb
16
comment Is it fair to judge this speedskating race by only 3 thousands of a second?
Don't forget the position of the sun which by its gravity influences time ...
Feb
16
comment Is it fair to judge this speedskating race by only 3 thousands of a second?
@JerrySchirmer A finish camera is in essence a continuous roll of film exposed through a slit aiming at the finish line while the film moves. This translates temporal order to spacial arrangement on the photo (and is responsible for the somewhat distorted shapes the runners get when moving their limbs while crossing the finish line). Not sure if this has changed in the digital ages, but maybe not (cause CCDs are read out sequentially).
Feb
14
comment What is the meaning of “background” in General Relativity?
There's no background, there's only background energy (aka. vacuum energy).
Jan
18
awarded  Informed
Jan
6
awarded  Supporter
Jan
6
comment Energy loss in pipe/hose with hot water (how its affected by pipe/hose size, temperature)?
From thermal loss, less surface seems to be the right thing to do. But note that the pressure needed to pump the water through smaller pipes is higher (Hagen-Poisseule law)
Sep
14
awarded  Autobiographer
Sep
13
answered Magnetic paradox in relativity?