Morning Coffee Physics: The Physicist’s Toolbox: Thought Experiments
Physics is an empirical science which means that you can do all the thinking and theorising you want, but at the end of the day, if it doesn’t match the real world experimental results, it’s wrong.
I’ve harped on this before. If you manage an unphysical result or contradiction in your thought experiment, it means your thought is wrong.
See also The Physicist’s Toolbox: Symmetry
EGNOS ‘Open Service’ available
EGNOS is the European Geostationary Navigation Overlay Service, which looks to be the European equivalent of WAAS, the Wide-Area Augmentation Service. Ground stations and geostationary satellites give corrections to GPS satellite position, timing and atmospheric time delay, which improves the positioning … if your receiver is compatible.
Satellite positioning and timing errors correspond pretty directly to positioning errors, so constant updating reduces errors. The atmospheric delay is a variable; if you have two frequencies you can figure out the ionosphere delay (it’s dispersive, so having two frequencies give two delays) but commercial GPS units only currently use 1 frequency; this will change with GPS III.
It’s only a model.
Found one of these in our group’s mailbox one recent morning.
Building a Model Block IIR(M) Satellite
Best result with titanium and space-hardened electronics heavy card stock.
The Boy Who Harnessed the Wind: Persistence, Jury-Rigging, and Ingenuity Against All Odds
A Malawian youth, whose family could not afford his school tuition, learns some physics and builds a windmill to generate electricity for his village.
William scoured trash bins and junkyards for materials he could use to build his windmill. With only a couple of wrenches at his disposal, and unable to afford even nuts and bolts, he collected things that most people would consider garbage-slime-clogged plastic pipes, a broken bicycle, a discarded tractor fan-and assembled them into a wind-powered dynamo. For a soldering iron, he used a stiff piece of wire heated in a fire. A bent bicycle spoke served as a size adapter for his wrenches.