Seven Medical Myths Busted - Fantasy Football Cafe 2014 Fantasy Football Cafe


Return to General Talk

Seven Medical Myths Busted

Moderator: Football Moderators

Re: Seven Medical Myths Busted

Postby eagles21 » Sat Dec 29, 2007 12:56 am

bagobonez wrote:Does hot water freeze faster than cold? Like... if you're filling up an ice cube tray to stick in your freezer? I've heard hot water freezes faster than cold water, but have never tested it. Anyone know?


Sometimes, called the Mpemba effect.

http://math.ucr.edu/home/baez/physics/G ... water.html

Hot water can in fact freeze faster than cold water for a wide range of experimental conditions. This phenomenon is extremely counter- intuitive, and surprising even to most scientists, but it is in fact real. It has been seen and studied in numerous experiments. While this phenomenon has been known for centuries, and was described by Aristotle, Bacon, and Descartes [1-3], it was not introduced to the modern scientific community until 1969, by a Tanzanian high school student named Mpemba. Both the early scientific history of this effect, and the story of Mpemba's rediscovery of it, are interesting in their own right -- Mpemba's story in particular provides a dramatic parable against making snap judgements about what is impossible. This is described separately below.

The phenomenon that hot water may freeze faster than cold is often called the Mpemba effect. Because, no doubt, most readers are extremely skeptical at this point, we should begin by stating precisely what we mean by the Mpemba effect. We start with two containers of water, which are identical in shape, and which hold identical amounts of water. The only difference between the two is that the water in one is at a higher (uniform) temperature than the water in the other. Now we cool both containers, using the exact same cooling process for each container. Under some conditions the initially warmer water will freeze first. If this occurs, we have seen the Mpemba effect. Of course, the initially warmer water will not freeze before the initially cooler water for all initial conditions. If the hot water starts at 99.9° C, and the cold water at 0.01° C, then clearly under those circumstances, the initially cooler water will freeze first. However, under some conditions the initially warmer water will freeze first -- if that happens, you have seen the Mpemba effect. But you will not see the Mpemba effect for just any initial temperatures, container shapes, or cooling conditions.

This seems impossible, right? Many sharp readers may have already come up with a common proof that the Mpemba effect is impossible. The proof usually goes something like this. Say that the initially cooler water starts at 30° C and takes 10 minutes to freeze, while the initially warmer water starts out at 70° C. Now the initially warmer water has to spend some time cooling to get to get down to 30° C, and after that, it's going to take 10 more minutes to freeze. So since the initially warmer water has to do everything that the initially cooler water has to do, plus a little more, it will take at least a little longer, right? What can be wrong with this proof?

What's wrong with this proof is that it implicitly assumes that the water is characterized solely by a single number -- the average temperature. But if other factors besides the average temperature are important, then when the initially warmer water has cooled to an average temperature of 30° C, it may look very different than the initially cooler water (at a uniform 30° C) did at the start. Why? Because the water may have changed when it cooled down from a uniform 70° C to an average 30° C. It could have less mass, less dissolved gas, or convection currents producing a non-uniform temperature distribution. Or it could have changed the environment around the container in the refrigerator. All four of these changes are conceivably important, and each will be considered separately below. So the impossibility proof given above doesn't work. And in fact the Mpemba effect has been observed in a number of controlled experiments
Image
eagles21
General Manager
General Manager

User avatar
CafeholicCafe RankerGraphics ExpertMock(ing) DrafterEagle EyeCafe Blackjack Weekly Winner
Posts: 4613
Joined: 7 Jun 2006
Home Cafe: Football
Location: State College, PA

Re: Seven Medical Myths Busted

Postby Lofunzo » Sun Dec 30, 2007 1:17 pm

Does hot water freeze faster than cold? Like... if you're filling up an ice cube tray to stick in your freezer? I've heard hot water freezes faster than cold water, but have never tested it. Anyone know?


Even if it does, it tastes like crap.
"There is no bad beer. Some are better than others."
Image
Lofunzo
Head Coach
Head Coach

User avatar
Baseball ModHockey Mod
Posts: 1287
Joined: 9 Jul 2003
Home Cafe: Baseball
Location: 2008 GOM: 6

Re: Seven Medical Myths Busted

Postby Metroid » Sun Dec 30, 2007 2:23 pm

eagles21 wrote:
Metroid wrote:Oh and Santa isn't real. :-b


Wha??? :,-(

Sorry man. :-b
Image
Metroid
Moderator
Moderator

User avatar
ModeratorCafeholicCafe RankerGraphics ExpertEagle Eye
Posts: 22544
Joined: 9 Oct 2005
Home Cafe: Football
Location: Bringing the funk in P-Town!

Re: Seven Medical Myths Busted

Postby Tiki » Sun Dec 30, 2007 6:22 pm

Metroid wrote:
eagles21 wrote:
Metroid wrote:Oh and Santa isn't real. :-b


Wha??? :,-(

Sorry man. :-b

Crushing a Dream...And you're not even Treat!
Keep it lit.
Tiki
Hall of Fame Hero
Hall of Fame Hero

User avatar
Graphics ExpertMock(ing) DrafterPick 3 ChampionSweet 16 SurvivorLucky Ladders Weekly Winner
Posts: 7020
Joined: 25 Nov 2003
Home Cafe: Football
Location: '08 DOM-35.

Re: Seven Medical Myths Busted

Postby josebach » Sun Dec 30, 2007 6:41 pm

The only two I really found suprising were the turkey one and the fingernails one. They were to myths I've personally perpetuated over the years. Good thread, Knapp!!! ;-D
Image
josebach
General Manager
General Manager

User avatar
Cafe Ranker
Posts: 4611
Joined: 27 Aug 2003
Home Cafe: Football
Location: Tallahassee, FL

Previous

Return to General Talk

Who is online

Users browsing this forum: No registered users and 1 guest

Forums Articles & Tips Start & Sit Sleepers Rankings Leagues


Get Ready...
The 2014 NFL season kicks off in 23:41 hours
(and 57 days)
2014 NFL Schedule


  • Fantasy Football
  • Article Submissions
  • Privacy Statement
  • Site Survey 
  • Contact