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Comment: Re:58 Second Burn? (Score 4, Informative) 160

by HawkinsD (#44563981) Attached to: Easily-Captured Asteroids Identified

Well, let's consider the damage from the impact of a rocky asteroid, 60m in diameter. Plug this into the excellent Earth Impact Effects program at http://impact.ese.ic.ac.uk/ImpactEffects/. Assume a velocity of 17 km/s, which they say is "typical for asteroids," and an impact angle of 45 degrees.

The calculator says:

        The projectile begins to breakup at an altitude of 54000 meters = 177000 ft
        The projectile bursts into a cloud of fragments at an altitude of 4700 meters = 15400 ft
        The residual velocity of the projectile fragments after the burst is 4.77 km/s = 2.96 miles/s
        The energy of the airburst is 4.52 x 1016 Joules = 1.08 MegaTons.
        No crater is formed, although large fragments may strike the surface.

Clearly you wouldn't want to be right underneath it, but even as close as 20 km, the air blast effects seem rather anticlimactic:

        Peak Overpressure: 18900 Pa = 0.189 bars = 2.69 psi
        Max wind velocity: 41.4 m/s = 92.6 mph
        Sound Intensity: 86 dB (Loud as heavy traffic)
        Damage Description:
                Glass windows will shatter.
                About 30 percent of trees blown down; remainder have some branches and leaves blown off.

So it'd be like BOOM! But not like KA-FOOOM!

For comparison, the Chelyabinsk meteor was estimated at 17-20m, with an airburst energy of 0.4 MegaTons.

Comment: Re:What could possibly go wrong? (Score 3, Insightful) 171

by HawkinsD (#42481859) Attached to: NASA Considers Putting an Asteroid Into Orbit Around the Moon

No, they defintely mean 7 meters. 500,000 kg. Which seems like a lot, if it's hitting your house at several miles per second.

But that's only 90,000 kg more than the ISS (http://www.nasa.gov/mission_pages/station/structure/isstodate.html).

On the other hand, I bet the ISS would burn up a lot better on its way towards your house.

Comment: Re:Launcher barrels rifled! (Score 1) 117

by HawkinsD (#37021210) Attached to: Build Your Own Camera, Launch It Like a Grenade

Mr. Elm:

That's a good point about the rifling. It appears that the Defcon fellows are using flare launchers, which, anecdotally, are described as smoothbore.

I dunno why flare launchers aren't rifled. Maybe the need for accuracy in shooting a flare is low: if it goes UP, instead of sideways, it's probably considered a success. The energy expended on making it spin could arguably be better spent on making it fly.

Education

200 Students Admit Cheating After Professor's Online Rant 693

Posted by samzenpus
from the people-get-what-they-deserve dept.
Over 200 University of Central Florida students admitted to cheating on a midterm exam after their professor figured out at least a third of his class had cheated. In a lecture posted on YouTube, Professor Richard Quinn told the students that he had done a statistical analysis of the grades and was using other methods to identify the cheats, but instead of turning the list over to the university authorities he offered the following deal: "I don't want to have to explain to your parents why you didn't graduate, so I went to the Dean and I made a deal. The deal is you can either wait it out and hope that we don't identify you, or you can identify yourself to your lab instructor and you can complete the rest of the course and the grade you get in the course is the grade you earned in the course."

Comment: Re:I don't care about "most dictionaries"... (Score 3, Informative) 180

by HawkinsD (#30339660) Attached to: Google Launches Dictionary, Drops Answers.com

That's really interesting, thanks. The main dictionary (oed.com) is $295/year. I didn't know they had a concise one for free.

And it really is concise. One (really good) definition. Not 37 links, like the Google dictionary.

Not that there's anything wrong with 37 links. But sometimes I just want to want to know the definition of the word.

Comment: I dunno, man. Snow is heavy (Score 2, Insightful) 456

by HawkinsD (#30032022) Attached to: Vermont City Almost Encased In a 1-Mile Dome

A couple of years ago Burlington, VT received 25.7 inches (0.65 m) of snow in 24 hours. I don't know what the density of snow is (I imagine it varies wildly), but that seems like a lot of weight.

OK, maybe the warm air can support that... but if that were the case, then on days when there wasn't 89 grillion kg of snow on top, there would be some pretty huge upward forces on the tent-pegs.

OK, well, then, there are vents, to let our some of the hot air. But then you waste all that energy heating air that you're venting.

But maybe it all works out somehow.

Comment: Re:Thatcher and Argentina (Score 4, Informative) 392

by HawkinsD (#29898259) Attached to: Trojan Kill Switches In Military Technology

Wait! I retract my earlier assertion.

According to this article (cited elsewhere in this thread by acb) about French President Mitterand, PM Thatcher successfully pressured the French to reveal the "codes to make the Exocets deaf and blind" after the Sheffield was sunk.

Very interesting.

Disks travel in packs.

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