Hagen von Eitzen

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111 reputation
bio website von-eitzen.de/math/tntrep.xml
location Bonn, Germany
age 48
visits member for 1 year, 10 months
seen 6 hours ago

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

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, ...)
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.
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 ...
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).
comment What is the meaning of “background” in General Relativity?
There's no background, there's only background energy (aka. vacuum energy).
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)