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Comment Re:What do you expect? (Score 1) 247

Hell, if we're just wishing for things, why not have the old functionality of AdBlock Plus built-in? I thought this was free software...

I still put up with Firefox, but it has been sold out years ago when they broke the extensions, raped the GUI to immitate Chrome and pushed crap like Pocket that nobody liked.

At this day and age, the trust between the user and the browser is more important than ever. The Mozilla management has broken this trust when they started acting like a company (i.e., like everybody else) rather like a FOSS community.

Comment Re:Remember (Score 3, Interesting) 69

Indeed. My thermodynamics teacher at the university was very specific about calling it an "axiom" not a "law" (all of them, in fact, not just the 2nd). He also didn't find it elegant that pretty much all of thermodynamics is based on three unproven axioms (or four, if you count the 0th). He was a proponent of the idea that thermodynamics should be based on as few axioms as possible, because you shouldn't just declare stuff true left and right without rigorous proof. He was therefore a fan of the single-axiom formulation of thermodynamics by Hatsopoulos and Keenan, where all three "standard" laws of thermodynamics can be derived from that one axiom. Needless to say, you had to do a lot of study to pass his class.

Comment Re:Drag force, coefficient of drag negative? (Score 1) 200

When the vehicle moves faster than the wind, the drag force *is* pointing backwards and it *does* try to slow down the vehicle.
The coefficient of drag is not a vector, it's just a scalar coefficient that's always positive. The sign of the drag *force* results from the sign of the *relative* speed (U_fluid - U_body), which will point backwards when the craft is moving faster than the air around it. You can choose the positive and the negative direction arbitrarily, but be *consistent*.

The fact that the vehicle is not brought to a stop by the drag force is because the vehicle has a propeller (*not* a turbine!) that is driven by the wheels. From a standsstill, as soon as the wind pushes the vehicle forward (drag force pointing forward), and the vehicle moves relative to the ground, the wheels will drive the propeller that will push the vehicle forward a bit more. The force of the wind and the propeller are both pointing forward and have the same sign. As the vehicle accelerates, the wind force will decrease down to zero when the vehicle velocity becomes equal to that of the wind. The drag force will be zero, but the drag coefficient is not defined at this point! But while the vehicle was accelerating, the force of the propeller was increasing, and as the drag was dropping its net effect was also increasing. At the point where U_fluid=U_body you still have the force of the turbine and no drag, which will accelerate the vehicle faster than the air around it. After that the drag force vector will switch sign and will point backwards, trying to slow the vehicle down. Eventually I suppose a terminal velocity will be reached where the force of the propeller will be equal to the drag force. No further acceleration will be possible beyond that point.

Comment Re:Ground speed? (Score 1) 146

Well, if we want to be pedantic for the sake of argument, the train is still bound to the ground, since it "hugs" the rail. Also, I think a hovercraft needs its skirts to extend all the way to the ground, which they touch sometimes if it is uneven. I would define a "non-ground" vehicle as such if its operator can change the altitude at will within the atmosphere. Or, let's say, if the operational altitude can exceed the height of the vehicle?

Comment Remarkable progress since the 60ies (Score 2) 23

It seems to me that all we achieved in the meantime was add three zeros to the budget. From John D. Clark's "Ignition!":

This was to get a computer, and to feed into it all known bond energies, as well as a program for calculating specific impulse. The machine would then juggle structural formulae until it had come up with the structure of a monopropellant with a specific impulse of well over 300 seconds. It would then print this out and sit back, with its hands folded over its console, to await a Nobel prize. The Air Force has always had more money than sales resistance, and they bought a one-year program (probably for something in the order of a hundred or a hundred and fifty thousand dollars) and in June of 1961 Hawkins and Summers punched the "start" button and the machine started to shuffle IBM cards. And to print out structures that looked like road maps of a disaster area, since if the compounds depicted could even have been synthesized, they would have, infallibly, detonated instantly and violently. The machine's prize contribution to the cause of science was the structure [ASCII-art filter does not accept chemical forumlas!], to which it confidently attributed a specific impulse of 363.7 seconds, precisely to the tenth of a second, yet. The Air Force, appalled, cut the program off after a year, belatedly realizing that they could have got the same structure from any experienced propellant man (me, for instance) during half an hour's conversation, and at a total cost of five dollars or so. (For drinks. I would have been afraid even to draw the structure without at least five Martinis under my belt.)

On a more serious tone, as someone that runs simulations on a computer cluster for a living, it's actually beneficial that we're using the technology for more than lolcat videos. But it's also hilarious how such stories have remained essentially unchanged for 60 years.

Comment Re:Why not go to the source? (Score 2) 122

The Challenger disaster, as Feynman discovered, was more due to a culture discrepancy between the political management and the pragmatic engineers. Concerning the notorious O-Rings, the upper management was operating under a distorted notion of the term "safety factor" where, in fact, there was none.

Alas, what you describe is closer to what happened with Columbia. Here we have a case where the problem was known and investigated, but the ball was dropped at the last critical minute of decision-making where the risk warnings were watered-down in the PowerPoint slides. It seems that managers have evolved to be so incompetent that they can't even take in a few bullet-points. They just read the final "executive summary" point. Although pretty much the whole slide was trying to warn of the risk, the final point was contradicting everything above it and was giving the go-ahead for the return.

You can read more about it here (scroll a bit down):
https://www.edwardtufte.com/bb...

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