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### What-if 0035: "Hair Dryer"

Posted: Tue Mar 05, 2013 9:56 am UTC
http://what-if.xkcd.com/35
What would happen if a hair dryer with continuous power was turned on and put in an airtight 1x1x1 meter box?

### Re: What-if 0035: "Hair Dryer"

Posted: Tue Mar 05, 2013 10:09 am UTC
Yeah, if it was STP in the box before it started, and the box was sealed, wouldn't the box give way at some point?

### Re: What-if 0035: "Hair Dryer"

Posted: Tue Mar 05, 2013 10:20 am UTC
Just one more, then we'll stop.

Why did I even bother reading that bit

### Re: What-if 0035: "Hair Dryer"

Posted: Tue Mar 05, 2013 10:21 am UTC

If the hair dryer was entirely inside the box then it wouldn't make a difference. It would only matter if the intake was outside the box and the output inside it, or vice versa.

What worries me is a) what's the hair dryer plugged into, and what kind of extension cord is allowing for all this flying around, and b) who's adjusting that dial?

Although given that it's a sealed box, I suspect the answer to the latter question is Schrodinger's cat.

### Re: What-if 0035: "Hair Dryer"

Posted: Tue Mar 05, 2013 10:30 am UTC
Does a higher-power hair dryer move more air, or just heat the air more? If the former, at higher settings could there be enough of a pressure difference between the front and back of the hairdryer to deform the box? Is the air inside the box going to approach 0.9c?

### Re: What-if 0035: "Hair Dryer"

Posted: Tue Mar 05, 2013 10:48 am UTC
jalohones wrote:

If the hair dryer was entirely inside the box then it wouldn't make a difference. It would only matter if the intake was outside the box and the output inside it, or vice versa.

What worries me is a) what's the hair dryer plugged into, and what kind of extension cord is allowing for all this flying around, and b) who's adjusting that dial?

Although given that it's a sealed box, I suspect the answer to the latter question is Schrodinger's cat.

I highly doubt that it would be Schrödinger's cat, because you have information while the box is closed, you could say something about lack of poisonous vials, but the heat would substitute for that. Lets say we do have Schrödinger's cat in there. Then the cat is alive so long as the dial is being changed, which can be determined by leaving the equilibrium state after having achieved it.

Not only by this information "leak" you could claim this (could be solved by having the cat turn it on 11 immediately, but then the cat is useless anyway), but the cat also manages to survive heat that normally vaporizes any metal. So the cat is indestructible, which is a fatal flaw for Schrödinger's experiment.

### Re: What-if 0035: "Hair Dryer"

Posted: Tue Mar 05, 2013 10:50 am UTC
This innocent fact about the volumetric power output of the sun at its core, due to Wikipedia always creeped me out:

Wikipedia wrote:The power production by fusion in the core varies with distance from the solar center. At the center of the Sun, theoretical models estimate it to be approximately 276.5 watts/m3, a power production density that more nearly approximates reptile metabolism than a thermonuclear bomb. Peak power production in the Sun has been compared to the volumetric heats generated in an active compost heap. The tremendous power output of the Sun is not due to its high power per volume, but instead due to its large size.

EDIT: It did NOT creep me out due to Wikipedia - I am, and have - with exceptions - always been, fairly comfortable around Wikipedia!

### Re: What-if 0035: "Hair Dryer"

Posted: Tue Mar 05, 2013 10:58 am UTC
But what if we tried more power?

### Re: What-if 0035: "Hair Dryer"

Posted: Tue Mar 05, 2013 11:20 am UTC
Regarding the nuclear-potato-manhole-cover: I think no amount of debate would conclusively settle the actual fate of that poor manhole cover, so the unescapable next step is clear as daylight: WE MUST DO IT AGAIN! FOR SCIENCE! This time with a proper high-speed camera, of course. I propose submitting the idea to the Mythbusters - what say you? Although I guess they might have to go a few notches higher than Frank Doyle for clearance this time - but how badass would that be, huh...?

### Re: What-if 0035: "Hair Dryer"

Posted: Tue Mar 05, 2013 11:23 am UTC
Wooloomooloo wrote:Regarding the nuclear-potato-manhole-cover: I think no amount of debate would conclusively settle the actual fate of that poor manhole cover, so the unescapable next step is clear as daylight: WE MUST DO IT AGAIN! FOR SCIENCE! This time with a proper high-speed camera, of course. I propose submitting the idea to the Mythbusters - what say you? Although I guess they might have to go a few notches higher than Frank Doyle for clearance this time - but how badass would that be, huh...?

My thoughts exactly.

### Re: What-if 0035: "Hair Dryer"

Posted: Tue Mar 05, 2013 11:55 am UTC
jalohones wrote:

If the hair dryer was entirely inside the box then it wouldn't make a difference. It would only matter if the intake was outside the box and the output inside it, or vice versa.

Heating a gas while keeping the volume and the number of moles present fixed increases the pressure of the gas. If the temperature inside the box gets high enough, then you start getting fusion taking place. Higher still, and you get a quark-gluon soup. Higher still and you break known physics...

### Re: What-if 0035: "Hair Dryer"

Posted: Tue Mar 05, 2013 11:58 am UTC
rmsgrey wrote:Heating a gas while keeping the volume and the number of moles present fixed increases the pressure of the gas. If the temperature inside the box gets high enough, then you start getting fusion taking place. Higher still, and you get a quark-gluon soup. Higher still and you break known physics...
An entirely unexplored line. At what point do we have a fusion reactor in the box - and if the ionising radiation can escape directly, for how far around is it deadly?

### Re: What-if 0035: "Hair Dryer"

Posted: Tue Mar 05, 2013 12:07 pm UTC
rmsgrey wrote:Higher still, and you get a quark-gluon soup.

I think that's on the menu at Heston Blumenthal's latest restaurant.

### Re: What-if 0035: "Hair Dryer"

Posted: Tue Mar 05, 2013 1:44 pm UTC
Wooloomooloo wrote:Regarding the nuclear-potato-manhole-cover: I think no amount of debate would conclusively settle the actual fate of that poor manhole cover, so the unescapable next step is clear as daylight: WE MUST DO IT AGAIN! FOR SCIENCE! This time with a proper high-speed camera, of course. I propose submitting the idea to the Mythbusters - what say you? Although I guess they might have to go a few notches higher than Frank Doyle for clearance this time - but how badass would that be, huh...?

Given that the only ones setting off nukes these days are in North Korea, I think Adam and Jamie will have to book a flight to Pyongyang

### Re: What-if 0035: "Hair Dryer"

Posted: Tue Mar 05, 2013 1:56 pm UTC
Ahh... not going to lie, I sure missed these catastrophic 'what-if's.

### Re: What-if 0035: "Hair Dryer"

Posted: Tue Mar 05, 2013 1:59 pm UTC
Screw an indestructable hair dryer, I want an exponential time travelling hair dryer. Even though, given its power surplus, it'd probably only go a few trillion years before the beginning of the universe.

### Re: What-if 0035: "Hair Dryer"

Posted: Tue Mar 05, 2013 2:43 pm UTC
Reecer6 wrote:Screw an indestructable hair dryer, I want an exponential time travelling hair dryer. Even though, given its power surplus, it'd probably only go a few trillion years before the beginning of the universe.

Ah, but what if we tried more power? Could we trigger a Big Bang?

### Re: What-if 0035: "Hair Dryer"

Posted: Tue Mar 05, 2013 2:51 pm UTC
rmsgrey wrote:
Reecer6 wrote:Screw an indestructable hair dryer, I want an exponential time travelling hair dryer. Even though, given its power surplus, it'd probably only go a few trillion years before the beginning of the universe.

Ah, but what if we tried more power? Could we trigger a Big Bang?

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`INSUFFICIENT DATA FOR MEANINGFUL ANSWER.`

### Re: What-if 0035: "Hair Dryer"

Posted: Tue Mar 05, 2013 3:23 pm UTC
Yes, but how quickly will 1.87 gigawatts dry my hair?

### Re: What-if 0035: "Hair Dryer"

Posted: Tue Mar 05, 2013 3:29 pm UTC
Daggertrout wrote:Yes, but how quickly will 1.87 gigawatts dry my hair?

Let's put it this way: remember back in 1985, when your hair wasn't wet?

There you go.

### Re: What-if 0035: "Hair Dryer"

Posted: Tue Mar 05, 2013 3:43 pm UTC
Ah, but on Back to the Future they didn't use gigawatts, they used something called jiggawatts.

### Re: What-if 0035: "Hair Dryer"

Posted: Tue Mar 05, 2013 3:54 pm UTC
Which they retconned when they realised it was mispronounced. Oh and it was 1.21Gw. Also, the pronounciation used in the film is an acceptable way to pronounce Gigawatt anyway.

### Re: What-if 0035: "Hair Dryer"

Posted: Tue Mar 05, 2013 4:05 pm UTC
jalohones wrote:

If the hair dryer was entirely inside the box then it wouldn't make a difference. It would only matter if the intake was outside the box and the output inside it, or vice versa.
.

No, you forgot P*V = n*k*T

Since the volume is fixed, the temperature rise means the pressure is rising too. Maybe the box will explode before it melts. But I guess Randall's uber-box here is not only melt-proof but explosion-proof.

### Re: What-if 0035: "Hair Dryer"

Posted: Tue Mar 05, 2013 4:07 pm UTC
Jackpot777 wrote:
rmsgrey wrote:
Reecer6 wrote:Screw an indestructable hair dryer, I want an exponential time travelling hair dryer. Even though, given its power surplus, it'd probably only go a few trillion years before the beginning of the universe.

Ah, but what if we tried more power? Could we trigger a Big Bang?

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`INSUFFICIENT DATA FOR MEANINGFUL ANSWER.`

yeah, thanks Mr. Asimov.

### Re: What-if 0035: "Hair Dryer"

Posted: Tue Mar 05, 2013 4:10 pm UTC
Now my hairdryer has also about 1875W (1800W to be exact).
I measured I need about 23 seconds to dry my hair with it.
I wonder if there is a time measuring unit small enough to tell how much time that 11 petawatt dryer would need.

### Re: What-if 0035: "Hair Dryer"

Posted: Tue Mar 05, 2013 4:12 pm UTC
Just going to mention one nit: he wrote a bit about being unable to touch a box made of metal once it gets above a certain temperature. This is a function of the material's thermal conductivity as well as its temperature. I saw a neat demo of the extremely small thermal conductivity (Tc) of the Space Shuttle's tiles once. You can heat them until they are glowing red ( the spectral radiant output is a function of temperature and all sorts of weird physics that get summarized into how much unlike a 'black body radiator' the material is) and hold them in your hands without injury. That's because the rate of energy flow via conduction is miniscule.

### Re: What-if 0035: "Hair Dryer"

Posted: Tue Mar 05, 2013 4:35 pm UTC
cellocgw wrote:Just going to mention one nit: he wrote a bit about being unable to touch a box made of metal once it gets above a certain temperature. This is a function of the material's thermal conductivity as well as its temperature.

Isn't that why he specified a metal box, and went on to compare that with a wooden box?

### Re: What-if 0035: "Hair Dryer"

Posted: Tue Mar 05, 2013 5:00 pm UTC
jgh wrote:Ah, but on Back to the Future they didn't use gigawatts, they used something called jiggawatts.

jigga what?

### Re: What-if 0035: "Hair Dryer"

Posted: Tue Mar 05, 2013 5:01 pm UTC
Jackpot777 wrote:
rmsgrey wrote:
Reecer6 wrote:Screw an indestructable hair dryer, I want an exponential time travelling hair dryer. Even though, given its power surplus, it'd probably only go a few trillion years before the beginning of the universe.

Ah, but what if we tried more power? Could we trigger a Big Bang?

Code: Select all

`INSUFFICIENT DATA FOR MEANINGFUL ANSWER.`

Let there be heat!

### Re: What-if 0035: "Hair Dryer"

Posted: Tue Mar 05, 2013 5:17 pm UTC
Now I want a lava box. For Christmas.

### Re: What-if 0035: "Hair Dryer"

Posted: Tue Mar 05, 2013 5:21 pm UTC
And that, Jimmy, is why we use circuit breakers.

### Re: What-if 0035: "Hair Dryer"

Posted: Tue Mar 05, 2013 5:44 pm UTC
rhomboidal wrote:Now I want a lava box. For Christmas.

This is kinda creepy considering the hidden alt text on one of the pictures:

"it's warmer than my parents! It's my new parents."

### Re: What-if 0035: "Hair Dryer"

Posted: Tue Mar 05, 2013 5:47 pm UTC
Plasma_Wolf wrote:So the cat is indestructible, which is a fatal flaw for Schrödinger's experiment.

It is well known that cats have nine lives.
Administering one fatal dose of poison (D) will only expend one of the cat's lives.
Hence, in order to actually kill the cat, you need nine fatal doses (9D)
Therefore a cat can be killed with a dose of 9D
Hence the fatal dose for a cat is 9D, by definition of fatal dose.
But cats have nine lives...
By induction, the fatal dose for a cat is infinite.
An infinite amount of poison would occupy an infinite volume.
Hence any finite size of vial will not contain a fatal dose.
Therefore, the cat is indestructible.
QED.

### Re: What-if 0035: "Hair Dryer"

Posted: Tue Mar 05, 2013 5:59 pm UTC
jalohones wrote:

If the hair dryer was entirely inside the box then it wouldn't make a difference. It would only matter if the intake was outside the box and the output inside it, or vice versa
There is a myth in the Malaysian area that if a circulating fan is left in a room while someone is sleeping in it and the doors and windows are closed then they will suffocate. Complete bunk but believable knowing anything about basic plane mechanics and faster moving air simulating lower pressure (i.e. bad science).

### Re: What-if 0035: "Hair Dryer"

Posted: Tue Mar 05, 2013 6:01 pm UTC
Klear wrote:
rhomboidal wrote:Now I want a lava box. For Christmas.

This is kinda creepy considering the hidden alt text on one of the pictures:

"it's warmer than my parents! It's my new parents."

Oj freaking site won't let me put in my shock at the what if images having alt text

### Re: What-if 0035: "Hair Dryer"

Posted: Tue Mar 05, 2013 6:11 pm UTC
Icalasari wrote:
Klear wrote:
rhomboidal wrote:Now I want a lava box. For Christmas.

This is kinda creepy considering the hidden alt text on one of the pictures:

"it's warmer than my parents! It's my new parents."

Oj freaking site won't let me put in my shock at the what if images having alt text

Whatever it was you just said, Pfhorrest came up with this javasript to enable it:

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`javascript:(function(){ h = document.getElementsByTagName("img"); for (i=0; i<h.length; i++) h.item(i).title = h.item(i).alt; })()`

Paste this into your address bar while viewing a what-if page and then hover your mouse above pictures as usual.

Or better yet, add this line to your boookmarks and use it whenever new what-if comes.

### Re: What-if 0035: "Hair Dryer"

Posted: Tue Mar 05, 2013 6:23 pm UTC
This was a good one. Hysterical. Like the one about stopping a freight train with machine guns one, it is truly worthy of reading to my brother.*

*: My brother, for some odd reason, doesn't like the xkcd comics, so when the What Ifs started, I said they were just from some random blog I found, and he of course loves them.

### Re: What-if 0035: "Hair Dryer"

Posted: Tue Mar 05, 2013 7:49 pm UTC
Klear wrote:...

Code: Select all

`javascript:(function(){ h = document.getElementsByTagName("img"); for (i=0; i<h.length; i++) h.item(i).title = h.item(i).alt; })()`

Paste this into your address bar while viewing a what-if page and then hover your mouse above pictures as usual.

Or better yet, add this line to your boookmarks and use it whenever new what-if comes.

Then you would miss out on the jokes because all the alt-texts seem to be converted to title-texts on the site already.

### Re: What-if 0035: "Hair Dryer"

Posted: Tue Mar 05, 2013 8:08 pm UTC
Klear wrote:Whatever it was you just said, Pfhorrest came up with this javasript to enable it:

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`javascript:(function(){ h = document.getElementsByTagName("img"); for (i=0; i<h.length; i++) h.item(i).title = h.item(i).alt; })()`

I what? When did this happen? Have I been coding in my sleep?

### Re: What-if 0035: "Hair Dryer"

Posted: Tue Mar 05, 2013 8:15 pm UTC
Pfhorrest wrote:
Klear wrote:Whatever it was you just said, Pfhorrest came up with this javasript to enable it:

Code: Select all

`javascript:(function(){ h = document.getElementsByTagName("img"); for (i=0; i<h.length; i++) h.item(i).title = h.item(i).alt; })()`

I what? When did this happen? Have I been coding in my sleep?

Oops... it was huangho. Turns out that somebody misattributed the script in a quote. That somebody was me.