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Human
2004-Nov-12, 07:10 AM
When you want to find out the truth about a myth or legend, wich sites do you usually use?

I often use http://www.snopes.com/ and http://www.howstuffworks.com/

I would like to know about more sites like that.

Wolverine
2004-Nov-12, 07:53 AM
Aside from the above, these are fun:

The Skeptic's Dictionary (http://www.skepdic.com/)
CSICOP (http://www.csicop.org/)
HistoryBuff.com (http://www.historybuff.com/)
The Straight Dope (http://www.straightdope.com/)

Avatar28
2004-Nov-12, 02:05 PM
You could also try the site for the Discovery Channel show Myth Busters. There are some pretty active forums there and a lot of myths are discussed there too.

pghnative
2004-Nov-12, 02:16 PM
I'm not convinced that "Myth Busters" always uses good science.

One myth they investigated was whether soda cans could explode in a car on a hot sunny day. To test this, they put a soda can in a toaster oven, and kept increasing the temperature. It exploded when the got the temp up to ~ 350. "Myth busted" they declared, since your car will never get to 350...

"**" I declared. They didn't seem to wait long enough to ensure the can was the same temp as the oven. I guarantee that the can will explode at ~ 212 when the water boils. If not cooler, depending on how much CO2 is given off during the heating.

Only one example, but I think they care more about putting on a good show then they do about carefully checking the science behind the myths.

BlueAnodizeAl
2004-Nov-12, 02:46 PM
"**" I declared. They didn't seem to wait long enough to ensure the can was the same temp as the oven. I guarantee that the can will explode at ~ 212 when the water boils. If not cooler, depending on how much CO2 is given off during the heating.



Wrong, boiling is a function of pressure not temperature, for instance water boils at 0`C in a vacuum. The can is under internal pressure, water boils at higher temps at higher pressure and at lower temps at lower pressures.

Edit: I can check the math, but over 300`F sounds about right for a soda can.

Argos
2004-Nov-12, 04:40 PM
What about this one about Urban Legends (http://www.snopes.com/)?

Wolverine
2004-Nov-12, 06:03 PM
What about this one about Urban Legends (http://www.snopes.com/)?

Already in the OP. :wink:

Sammy
2004-Nov-12, 06:14 PM
What about this one about Urban Legends (http://www.snopes.com/)?
(emphasis added)

The link goes to their reference page. Did you mean to say "to" instead of "about," or is the link wrong?

Argos
2004-Nov-12, 06:16 PM
No, no, the mistake is mine. I didnīt see the link in the OP. Been working too much lately... :oops:

Makgraf
2004-Nov-12, 09:30 PM
Well there's always this site (http://www.badastronomy.com/) :)

I don't know how accurate Myth Busters is, but whenever I've seen it I've found it very entertaining.

Normandy6644
2004-Nov-12, 09:44 PM
Another good one is truth or fiction (www.truthorfiction.com).

pghnative
2004-Nov-12, 10:03 PM
"**" I declared. They didn't seem to wait long enough to ensure the can was the same temp as the oven. I guarantee that the can will explode at ~ 212 when the water boils. If not cooler, depending on how much CO2 is given off during the heating.



Wrong, boiling is a function of pressure not temperature...300 F sounds about right.Well that's embarrassing -- my brain was not completely engaged when I wrote that. My assumption is that the can cannot hold much internal pressure, so once you have significant vaporization, the can would fail.

Now at 300F, water generates ~ 65 psi of pressure. Plus the evolved CO2. Could the can hold this?? Maybe I'm off base here too.

BlueAnodizeAl
2004-Nov-13, 01:12 AM
Probably, I did a little research on it and a can's internal pressure at room temperature is about 2.25 atm. I need to look into my old thermodynamics books to get some numbers for you, but I would say with a decent factor of safety (which all pressurized containers have) I'd say it could hold at that temperature atleast for a few minutes. The real question is at what temperature does water boil at under this kind of pressure? I'll be right back with that answer.

Still haven't found it, it's hard to find in five years worth of notes #-o , but I think this diagram shows the idea pretty well, that the boiling temperature will get very, very high under pressure.
http://www.uiowa.edu/~c004131a/f8_3.gif

Edit: Finally, one (http://chem.skku.ac.kr/~wkpark/tutor/mirror/www.martin.chaplin.btinternet.co.uk/images/phase.gif) with some numbers if small.

Edited: to clean it up.

Note that 10^3 Pa is 1kPa

BlueAnodizeAl
2004-Nov-13, 01:53 AM
After making some guesstimates at the numbers on that chart (I hate logarithmic scaling, looks nice, but getting meaningful numbers out of it is a pain)...
I'm looking at the point of 10^5 Pa (which is atmospheric pressure) and move up one notch (about 2 times atmosphere) which makes the boiling temp ~420K...which is approximately 295`F. Someone check me on this.

Enzp
2004-Nov-13, 09:09 AM
Sorta related, is the Museum of Hoaxes website. Fun stuff there. if you are not sure if something is straight or a hoax, check them out.

Eroica
2004-Nov-13, 10:50 AM
One myth they investigated was whether soda cans could explode in a car on a hot sunny day. To test this, they put a soda can in a toaster oven, and kept increasing the temperature. It exploded when the got the temp up to ~ 350. "Myth busted" they declared, since your car will never get to 350...
Surely the correct way to test this "myth" is to load a car with cans of soda, drive out to the Death Valley, and see what happens? :D

pghnative
2004-Nov-15, 02:18 PM
After making some guesstimates at the numbers on that chart (I hate logarithmic scaling, looks nice, but getting meaningful numbers out of it is a pain)...
I'm looking at the point of 10^5 Pa (which is atmospheric pressure) and move up one notch (about 2 times atmosphere) which makes the boiling temp ~420K...which is approximately 295`F. Someone check me on this.My numbers (60 psi at 300F) are accurate. Took them from a thermo book, but you can easily find references on the web, such as here. (http://www.efunda.com/materials/water/steamtable_sat.cfm)

This doesn't include all of the CO2, the majority of which will come out of solution as the can heats.

Can an aluminum can with a pop-tab opening withstand 60+ pounds of pressure? Or will it fail at much lower pressures. I would have rather seen "Myth Busters" take this kind of scientific approach, rather than stick a can into a toaster oven and turn up the heat until the can burst. Maybe they waited enough time to heat the entire can at each temperature setting, or maybe they didn't. But they didn't say it, so I was left unimpressed.

BlueAnodizeAl
2004-Nov-15, 02:49 PM
Can an aluminum can with a pop-tab opening withstand 60+ pounds of pressure? Or will it fail at much lower pressures. I would have rather seen "Myth Busters" take this kind of scientific approach, rather than stick a can into a toaster oven and turn up the heat until the can burst. Maybe they waited enough time to heat the entire can at each temperature setting, or maybe they didn't. But they didn't say it, so I was left unimpressed.

Sounds like a Solid Mechanics: Pressure Vessel problem to me, I can work it out tonight? They probably left it in long enough.

I just happened to think of this: that as the can's temperature increases so does the internal pressure, which inturn raises the boiling point. At some point you will reach the failure of the can, before the boiling point of the liquid inside. I imagine it can get very, very hot before that happens.

So if you're interested in figuring this out mathematically, we need to the internal pressure of the can at the oven temperature (edit: which you've done), then we need to do a pressure vessel problem to find out the critical pressure the can is able to maintain and see what comparison can be made.

Perhaps we can move this into it's own thread? Since it's straying from the original topic by quite a bit.

Human
2004-Dec-21, 01:23 PM
I have found 2 great sites to add to the list:

http://urbanlegends.about.com/od/internet/a/top_10_uls.htm

http://www.darwinawards.com/legends/