Search found 179 matches

by Sandor
Wed Jul 03, 2013 7:32 am UTC
Forum: Science
Topic: So why can't we bulk produce space probes?
Replies: 25
Views: 9543

Re: So why can't we bulk produce space probes?

I'm going to reformulate. Sending two identical probes is almost as expensive as two different ones. Sometimes, you want to make the same tests in different places, but more often, it's smarter to use the results of the first probe to design new experiments for the second probe. ESA's Venus Express...
by Sandor
Mon Jun 03, 2013 12:37 pm UTC
Forum: Logic Puzzles
Topic: Can you crack this code?
Replies: 9
Views: 6319

Re: Can you crack this code?

The answer (and nothing but the answer)
Spoiler:
CONGRATULATIONS
by Sandor
Mon Jun 03, 2013 9:26 am UTC
Forum: Logic Puzzles
Topic: Hats
Replies: 42
Views: 15028

Re: Hats

Xias wrote:
Sandor wrote:Some rubbish

I disagree with this.

Yup. You're right, and I was wrong.
by Sandor
Mon Jun 03, 2013 8:15 am UTC
Forum: Logic Puzzles
Topic: Hats
Replies: 42
Views: 15028

Re: Hats

Anyway, follow up question that I really hope I didn't miss something obvious for: If there are fifty rats, can the non-rats get at least one point? I think they can get at least 16 points. They can split into 33 groups of 3 (with 1 left over) and then use the parity method with each group....
by Sandor
Fri May 24, 2013 8:41 am UTC
Forum: Language/Linguistics
Topic: Size-based intensity for written laughs
Replies: 13
Views: 8756

Re: Size-based intensity for written laughs

Writing "hahahahahahahahahahahaha" seems like bad form, doesn't it? But people do use it. Here's the search result counts I get from Google: "haha" 520,000,000 results "hahaha" 248,000,000 results "hahahaha" 95,400,000 results "hahahahaha" 39,500,00...
by Sandor
Tue May 14, 2013 12:21 pm UTC
Forum: Science
Topic: Orbital Maglev Vactrain
Replies: 28
Views: 4643

Re: Orbital Maglev Vactrain

Now, a 500 meter deep (for example) tunnel would certainly be quite an undertaking, but I think it is doable, and gets you quite a bit of speed. Not really. A 500 meter deep tunnel would only get you up to 360 Km/h, as compared to 300 - 320 Km/h for conventional high speed rail. The world's deepest...
by Sandor
Fri May 10, 2013 7:56 pm UTC
Forum: Individual XKCD Comic Threads
Topic: 1210: "I'm so random"
Replies: 242
Views: 40076

Re: 1210: "I'm so random"

I'm pretty disturbed by the "Customers Who Viewed This Item Also Viewed" section, though. White face paint... The Best of David Hasselhoff ... and a fresh whole rabbit. I'm not seeing The Best of David Hasselhoff , but I do see The 2009-2014 Outlook for Wood Toilet Seats in Greater China :?
by Sandor
Wed Apr 24, 2013 11:12 am UTC
Forum: Individual XKCD Comic Threads
Topic: 1203: "Time Machines"
Replies: 100
Views: 34302

Re: 1203: "Time Machines"

Should be "systems normal," no? No. Ever watched the live stream of a NASA launch? They always use 'nominal'. This means the systems are operating within the range they were designed for. It's a more exact and clearer wording than normal, and also a kind of jargon. My dictionary says this...
by Sandor
Mon Feb 18, 2013 7:01 am UTC
Forum: Individual XKCD Comic Threads
Topic: 1175:"Moving Sidewalks"
Replies: 78
Views: 21724

Re: 1175:"Moving Sidewalks"

HagarTopeka1 wrote:This one reminds me of Asimov's The Caves of Steel, where moving walkways are a primary form of high-speed public transportation.

For me, Heinlein's The Roads Must Roll immediately sprung to mind. That had 100 mph rolling roads, although glass partitions prevented high-fives (and wind shear).
by Sandor
Thu Feb 07, 2013 2:45 pm UTC
Forum: Fictional Science
Topic: A (Simple?) Physics Problem
Replies: 39
Views: 16168

Re: A (Simple?) Physics Problem

Are you sure about that speed? That paper says in the introduction that the face of the gas cloud expands at the speed of sound, not Mach 3.5. But I don't even know what that gamma they used is, so there's a high change that I'm misreading it. (I'm wondering for a slightly off-topic reason.) No, I'...
by Sandor
Mon Feb 04, 2013 4:30 pm UTC
Forum: Fictional Science
Topic: A (Simple?) Physics Problem
Replies: 39
Views: 16168

Re: A (Simple?) Physics Problem

Ignoring air resistance, http://en.wikipedia.org/wiki/Escape_velocity However, would there be significant air resistance? The air would be flying off at the same rate as everyone else. I think there would be, yes. But not nearly enough to prevent escape. People on the prograde side would suddenly f...
by Sandor
Thu Jan 10, 2013 3:43 pm UTC
Forum: Logic Puzzles
Topic: Solve ALL of the Mazes [solutions]
Replies: 29
Views: 9033

Re: Solve ALL of the Mazes [solutions]

Assumption : After k simultaneous moves away from the exits of A and B, it is possible to solve A and B simultaneously in k moves or less. That's clearly false. Consider these two fragments: A: # ## B: #### #X # X # # ## # ## # E# # E# #### #### The Es mark the exit squares, and the Xs mark the rob...
by Sandor
Wed Jan 02, 2013 4:18 pm UTC
Forum: Science
Topic: Suit of armor + Electric shock = ?
Replies: 20
Views: 5902

Re: Suit of armor + Electric shock = ?

The parallel circuit logic doesn't exactly apply here, since currents tend to flow on the outside of the conductor, and the higher the voltage the greater is this tendency. I think you're talking about the skin effect . Is so, that only applies to alternating current. The higher the frequency, the ...
by Sandor
Wed Jan 02, 2013 1:49 pm UTC
Forum: What If?
Topic: What-If 0026: "Leap Seconds"
Replies: 79
Views: 28529

Re: What-If 0026: Leap Seconds

More seriously, I worry about leap seconds. I worry about the repeated attempts to get rid of them, apparently by people who don't actually believe that a net constant slow-down of rotation means a quadratic difference between apparant time and TAI. Sure, leap seconds isn't a permanent patch, but, ...
by Sandor
Tue Nov 06, 2012 12:55 pm UTC
Forum: What If?
Topic: What-If 0019: "Tie Vote"
Replies: 57
Views: 32664

What-If 0019: "Tie Vote"

http://what-if.xkcd.com/19/

Nobody is known to have actually been killed by a meteorite. The 1 in 700,000 odds are heavily influenced by the (small) chance of a dinosaur killer wiping out everyone on earth. Some more info.
by Sandor
Tue Nov 06, 2012 11:20 am UTC
Forum: Logic Puzzles
Topic: Identifying upside-down cards
Replies: 5
Views: 2401

Re: Identifying upside-down cards

Off the top of my head, here's my suggestion: The magician turns over any strictly increasing/decreasing subset of cards. ie. When the assistant looks at the cards and sees that (by elimination) '2', '5', '7' and '9' are all face down, he knows they will be i...
by Sandor
Wed Oct 31, 2012 4:10 pm UTC
Forum: Science
Topic: How does space differ from time?
Replies: 78
Views: 19563

Re: How does space differ from time?

Greg Egan's most recent science fiction trilogy, Orthogonal , might be worth a read. It's set in a universe which is essentially 4t0s (or 4s0t; whatever). Aside from a few minor oddities, his characters mostly don't notice the difference until they start investigating relativity-type questions. (Wh...
by Sandor
Thu Oct 11, 2012 4:37 pm UTC
Forum: Individual XKCD Comic Threads
Topic: 1119: "Undoing"
Replies: 121
Views: 23799

Re: 1119: "Undoing"

Fortunately, it is physically impossible for things to blow up for absolutely no reason. Except for maybe the universe. As Terry Pratchett put it: "In the beginning there was nothing, which exploded." Although here, "nothing" means absolutely nothing, no space, no time, no anyth...
by Sandor
Mon Oct 08, 2012 8:16 am UTC
Forum: Logic Puzzles
Topic: I like cake and ice cream
Replies: 2
Views: 1696

Re: I like cake and ice cream

ThirdParty wrote:Here's my solution

Well done :) This puzzle was in a UK paper many years ago. You make it sound fairly easy, but I seem to remember it taking me ages.
by Sandor
Sun Oct 07, 2012 4:55 am UTC
Forum: Logic Puzzles
Topic: I like cake and ice cream
Replies: 2
Views: 1696

I like cake and ice cream

Newbie11's zahlenspiel reminded me of this similar addition puzzle:

Code: Select all

    I
 LIKE
 CAKE
  AND
  ICE +
-----
CREAM

Each letter represents a unique digit. There are no leading zeros in any of the numbers. There is more than one solution - the challenge is to find any one of them (by hand).
by Sandor
Fri Oct 05, 2012 2:29 pm UTC
Forum: Logic Puzzles
Topic: Zahlenspiel
Replies: 10
Views: 3157

Re: Zahlenspiel

jaap wrote:So this puzzle is a hoax, wrong, or incomplete.

I came to the same conclusion, with the same reasoning, but you beat me to the punch. I had my argument all typed out and ready to post. I even used the same letter substitutions. :(
by Sandor
Sat Sep 29, 2012 9:54 am UTC
Forum: Individual XKCD Comic Threads
Topic: 1114: "Metallurgy"
Replies: 138
Views: 30512

Re: 1114: "Metallurgy"

It's not about sticking it together so much as it is the fact that to remain at hyper density it has to remain constantly under pressure several times greater than that at the center of the Earth. Several time greater? The pressure at the centre of the Earth is around 10 11 pascals, and the electro...
by Sandor
Sat Sep 29, 2012 9:16 am UTC
Forum: Science
Topic: Why is the space program located at sea level?
Replies: 31
Views: 9393

Re: Why is the space program located at sea level?

At sea, though, you have at least some insulation from the landbound political situation...but it's most definitely a big investment in space travel over current facilities. I suspect you'd need to do rather a lot of launching there to make it worthwhile. It's already being done. Sea Launch have ha...
by Sandor
Fri Sep 28, 2012 2:15 pm UTC
Forum: Individual XKCD Comic Threads
Topic: 1114: "Metallurgy"
Replies: 138
Views: 30512

Re: 1114: "Metallurgy"

I'm not sure the asteroid's surface is superheated. IIRC what gets superheated is the air being compressed at insane speeds in front of the asteroid. Considering billions of years in the cold of space, against some seconds falling through atmosphere, I guess the meteor would still be quite cold aft...
by Sandor
Tue Sep 18, 2012 7:24 pm UTC
Forum: What If?
Topic: What-If 0012: "Raindrop"
Replies: 91
Views: 25410

Re: What-if 0012: Raindrop

geniekid wrote:There's absolutely no doubt in my mind that Randall started with the Skrillex punchline and worked backwards to pick the question.

I must live in a cave, because I didn't get it. For anyone else wondering, Google found me this
by Sandor
Thu Sep 06, 2012 11:39 pm UTC
Forum: Language/Linguistics
Topic: Some expressions in English (possibly regional)
Replies: 2
Views: 2165

Re: Some expressions in English (possibly regional)

eSOANEM wrote:I have heard the "fell off the back of a truck" one.

So have I, except it was always "fell of the back of a lorry". Truck implies an American phrase, and I always thought it was British.
by Sandor
Thu Sep 06, 2012 10:24 pm UTC
Forum: Logic Puzzles
Topic: 5 Cards, Choose 4
Replies: 7
Views: 5875

Re: 5 Cards, Choose 4

That thread includes a proof that this is possible with a pack of up to 124 cards (5!+4). After much squinting at Wikipedia (I don't know any graph theory) I've convinced myself of the proof's validity. So, can anyone come up with a simple method to solve this with more cards - say two packs of card...
by Sandor
Fri Aug 24, 2012 8:13 am UTC
Forum: Individual XKCD Comic Threads
Topic: 1099: "Tuesdays"
Replies: 71
Views: 17756

Re: 1099: "Tuesdays"

javahead wrote:Also, he's going to burn his wings on a star at some point, no?

I wonder if the solution to Olbers' paradox could help answer that.
by Sandor
Thu Aug 23, 2012 4:28 pm UTC
Forum: Science
Topic: Billiard balls - where does the energy go?
Replies: 25
Views: 5812

Re: Billiard balls - where does the energy go?

Billiard balls also have (to some extent) the problem of spin, similar to the cans experiment, at least if you roll them towards each other. Newton's cradles and Clackers (or Clacker Balls, or Ker-Bangers) don't spin, so are better tools to experiment with. Try a YouTube search for clackers.
by Sandor
Fri Aug 17, 2012 2:14 pm UTC
Forum: What If?
Topic: What-if 0007: "Everybody Out"
Replies: 350
Views: 64839

Re: What-if 0007: Everybody Out

...space elevators have their center of mass so high because that way they don't have to move relative to Earth's surface. At any other height, you're either wasting energy keeping it synched with Earth's rotation, or it's moving at quite a clip relative to Earth's surface... For lower (and shorter...
by Sandor
Wed Aug 15, 2012 4:33 pm UTC
Forum: What If?
Topic: What-if 0007: "Everybody Out"
Replies: 350
Views: 64839

Re: What-if 0007: Everybody Out

The construction of the Ring Rail itself seems pretty implausible - it would have to be about 40 megameters long (Circumference of Earth) and probably need huge supports at regular intervals - although possibly the ring structure would hold itself up, and it would only need 'spokes' to tether it in...
by Sandor
Wed Aug 15, 2012 2:34 pm UTC
Forum: Science
Topic: solid fuel rockets from the moon
Replies: 5
Views: 3096

Re: solid fuel rockets from the moon

You're not the first person to think of this. Here's a thread on nasaspaceflight.com that discusses the idea. From my reading of that thread (it's quite technical), an aluminium-oxygen rocket is indeed possible. It's even been tested , and might be feasible on the moon. For what it's worth, a mixtur...
by Sandor
Wed Aug 15, 2012 10:02 am UTC
Forum: What If?
Topic: What-if 0007: "Everybody Out"
Replies: 350
Views: 64839

Re: What-if 0007: Everybody Out

I'm curious about what would happen to the object on the other end of the space elevator as humans are climbing it. I'm thinking it would deorbit slowly and require a constant boost depending on how many people are climbing it at once. In principle, yes. You need to add both potential energy (heigh...
by Sandor
Mon Aug 13, 2012 2:28 pm UTC
Forum: Individual XKCD Comic Threads
Topic: 1094: "Interview"
Replies: 59
Views: 21142

Re: 1094: "Interview"

It looks like the briefcase fell through the hole along with the interviewer. How did it manage that?
by Sandor
Thu Aug 02, 2012 2:55 pm UTC
Forum: Logic Puzzles
Topic: Planting 10 trees in an orchard - 5 rows with 4 in each row
Replies: 8
Views: 18175

Re: Planting 10 trees in an orchard - 5 rows with 4 in each

This might be the answer to task 4 with bonus: I found a third pattern that fits in an 8x8 orchard (also based on the pin-art design, but with the rows of pins at 45 degrees). It can be reflected and rotated to fit in four copies plus the owner's house: B A A B A B B A . D A . . B C . . ...
by Sandor
Thu Aug 02, 2012 8:03 am UTC
Forum: Logic Puzzles
Topic: Planting 10 trees in an orchard - 5 rows with 4 in each row
Replies: 8
Views: 18175

Re: Planting 10 trees in an orchard - 5 rows with 4 in each

Are there any other patterns available? I think finding that out is part of the tasks! ;) Some thoughts on that (including some pretty big spoilers if you are stuck on task 1, but no actual usable patterns): The two patterns I used were both based on what I called a "string art" design, l...
by Sandor
Wed Aug 01, 2012 3:23 pm UTC
Forum: Logic Puzzles
Topic: Planting 10 trees in an orchard - 5 rows with 4 in each row
Replies: 8
Views: 18175

Re: Planting 10 trees in an orchard - 5 rows with 4 in each

Moose Anus wrote:I can't even get past task 1. I only have 10 trees, but you want a total of 20?

I suspect the word "row" is causing confusion, as it implies parallel lines. The lines of trees can cross, so a given tree can be in more than one line.
by Sandor
Wed Aug 01, 2012 11:19 am UTC
Forum: Logic Puzzles
Topic: Planting 10 trees in an orchard - 5 rows with 4 in each row
Replies: 8
Views: 18175

Re: Planting 10 trees in an orchard - 5 rows with 4 in each

Task 1: . . . . . . . . A . . . . . . . A . . . . . . . . A . . . . . . A . . . . . . . . . A . . . . . . . . . A . . . A . . A . A A . Task 2: B . . . . . B . A . . . . . . . A B B . B B . . . A . B . . . . A . B . B . . . . . A . . . . . . . . B A . . . A . . A . A A . First part of task 3: B . . ...
by Sandor
Mon Jul 30, 2012 3:12 pm UTC
Forum: Science
Topic: calculate the cooling power of single hose portable ACs
Replies: 5
Views: 2313

Re: calculate the cooling power of single hose portable ACs

The OP's figures for the volumes of air do not include a timescale, but I would assume that it is cooling 400m 3 of air by 10 degrees per hour . If so, then it seems fair enough to convert 3000W of "cooling power" to 3000Wh of "cooling energy" (i.e. it extracts 3000Wh of energy f...

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