OMG! Now I understand why we invaded Iraq!

[Amianthus]

(Note: modified. shouldn't post before drinking morning coffee. replaced all occurances of "second law of thermodynamics" with "first law of thermodynamics".)

I don't see that as fanciful in the least.

The theory is fanciful, because it violates the First Law of Thermodynamics.

You cannot get a pressure increase into the cup after the lid is put on it to cause enough of a pressure drop to cause boiling, without adding thermal energy after the cup is sealed. I mean, it's pretty simple to understand, as well. The pressure increase is caused by evaporation of the coffee. Evaporation of the coffee causes a temprature drop in the liquid. Removing the lid will then cause a temporary decrease in the vapor pressure above the coffee. However, the First Law of Thermodynamics says that the total energy transfer will always be at a loss - so therefore the initial temperature drop will never be overcome by the decrease in vapor pressure caused by the removal of the lid.

You're ignoring some pretty basic chemistry and physics.

If only we didn't have that pesky First Law of Thermodynamics. Then we'd have perpetual motion machines.

[Xavier_Onassis]

The bottom line in the McDonalds coffee case was whether the woman was seriously burned, and she was.

All she asked for in the beginning was the cost of visiting her doctor: under $200. If Mc Donald's has paid this small amount, the later lawsuit would not have occurred, and they would have saved a fortune in legal bills.
 

[Amianthus]

The bottom line in the McDonalds coffee case was whether the woman was seriously burned, and she was.

I can understand McDonald's point, however. The lady should have know that coffee is hot and would burn her if she spilled it on herself.

All she asked for in the beginning was the cost of visiting her doctor: under $200. If Mc Donald's has paid this small amount, the later lawsuit would not have occurred, and they would have saved a fortune in legal bills.

I agree. However, the result of the lawsuit is that now McDonald's has signs up at the cash register and on their coffee cups saying that coffee is hot and you can burn yourself if you spill it on yourself. And they're pretty much insulated from lawsuits now.

[Michael Tee]

Here's the First Law of Thermodynamics from Wikipaedia:
The increase in the internal energy of a thermodynamic system is equal to the amount of heat energy added to the system minus the work done by the system on the surroundings.

Basically, it's a restatement of the law of conservation of energy, that in a closed system energy can neither be created nor destroyed.  This does not prevent a transformation of energy from one form to another.

In the closed coffee cup, the heat energy of the liquid molecules acts to evaporate surface water into vapor, effectively converting the kinetic energy of the liquid into the kinetic energy of the vapor (increasing the atmospheric pressure inside the system) until an equilibrium is reached - - because of the interior atmospheric pressure, no more evaporation is possible.  (Since the cup is not a perfect insulator, heat will be lost to the exterior over time, but we are talking of a very short interval here where that factor should be ignored for the purposes of the discussion.)

Of course the evaporation requires energy, which cools the contents; but the energy which evaporated water from the surface was not lost - - it was converted to the kinetic energy of the vapor, so that as the temperature dropped, the internal atmospheric pressure rose.

An exterior force then acts upon the system - - the lid is dislodged, the vapor escapes, the pressure drops, the boiling point lowers and (theoretically, depending on the numbers) the liquid boils.  The First Law of Thermodynamics remains intact as does its broader incarnation, the law of conservation of energy, Stella suffers terrible burns and the law of torts now comes into play.

Q.E.D.

BTW, to XO as well:  bottom line was that a simple governor available at a cost of under $200 per unit could have prevented the superheated water which did so much damage to poor old Stella; and to Ami, EVERYBODY knows coffee is hot but that still doesn't stop the statistically inevitable spill.  It was for failing to take reasonable consequences against that inevitabilty, and in fact condemning the most careless fractional percentage of its customers to suffer otherwise avoidable third-degree burns, that McDonalds was eventually nailed.

[Amianthus]

Of course the evaporation requires energy, which cools the contents; but the energy which evaporated water from the surface was not lost - - it was converted to the kinetic energy of the vapor, so that as the temperature dropped, the internal atmospheric pressure rose.

An exterior force then acts upon the system - - the lid is dislodged, the vapor escapes, the pressure drops, the boiling point lowers and (theoretically, depending on the numbers) the liquid boils.  The First Law of Thermodynamics remains intact as does its broader incarnation, the law of conservation of energy, Stella suffers terrible burns and the law of torts now comes into play.

Q.E.D.

First of all, adding kinetic energy (removing the lid) only acts on the lid, it will not add thermal energy to the rest of the system. If there was not enough energy in the system to boil the liquid before the lid was put on, there will not be enough energy in the system when the lid is removed to boil the liquid because of inherent energy losses. The liquid may have been hot, but it was no closer to boiling when Stella removed the lid than it was when it was poured originally - actually, it is required to be further from the boiling point. Superheating does not apply (is not possible) in this situation.

Q.E.D.

[Amianthus]

and in fact condemning the most careless fractional percentage of its customers to suffer otherwise avoidable third-degree burns, that McDonalds was eventually nailed.

Stella did not have third-degree burns. Had she had third-degree burns (characterized by skin charring and the destruction of nerve endings in the skin) she would not have been in pain. Third-degree burns involve a loss of feeling the area.

Her testimony included the intense pain associated with scalding and second-degree burns.

[Michael Tee]

<<Stella did not have third-degree burns. Had she had third-degree burns (characterized by skin charring and the destruction of nerve endings in the skin) she would not have been in pain. Third-degree burns involve a loss of feeling the area.>>


from the Wikipedia article on Stella Liebeck-

<<Liebeck was wearing cotton sweatpants; they absorbed the coffee and held it against her skin as she sat in the puddle of hot liquid for over 90 seconds, scalding her thighs, buttocks, and groin.[5] Liebeck was taken to the hospital, where it was determined that she had suffered third-degree burns on six percent of her skin and lesser burns over sixteen percent.[6] She remained in the hospital for eight days while she underwent skin grafting. Two years of treatment followed.>>

[Mucho]

<<Stella did not have third-degree burns. Had she had third-degree burns (characterized by skin charring and the destruction of nerve endings in the skin) she would not have been in pain. Third-degree burns involve a loss of feeling the area.>>


from the Wikipedia article on Stella Liebeck-

<<Liebeck was wearing cotton sweatpants; they absorbed the coffee and held it against her skin as she sat in the puddle of hot liquid for over 90 seconds, scalding her thighs, buttocks, and groin.[5] Liebeck was taken to the hospital, where it was determined that she had suffered third-degree burns on six percent of her skin and lesser burns over sixteen percent.[6] She remained in the hospital for eight days while she underwent skin grafting. Two years of treatment followed.>>

Michael- You see what I mean. The idiot savant, Ami , knows facts , but not the meaning. It never occurs to these anal retentives that there can be more than one degree of anything. They dont do nuance, remmber? That means that they dont do thinking . Probly since they are incapable of any of that needless thinking stuff.

[Michael Tee]

<<First of all, adding kinetic energy (removing the lid) only acts on the lid, it will not add thermal energy to the rest of the system. >>

Nice reasoning, but kind of a waste since I did not argue that the removal of the lid added kinetic energy to the system.  The lid in place was a nice illustration of Newton's Third Law - - the kinetic energy of the vapor and hot air pressing up on the lid was met with the downward pressure exerted by the lid on the combined gases.  When the lid was removed, the kinetic energy of the gas molecules was transferred to the ambient air molecules outside the cup and there was significantly less kinetic energy to provide atmospheric pressure on the surface of the liquid.

<<If there was not enough energy in the system to boil the liquid before the lid was put on, there will not be enough energy in the system when the lid is removed to boil the liquid because of inherent energy losses. >>

Forgetting that in theory at least, the decrease in atmospheric pressure on the surface of the liquid lowers the boiling point so that less thermal energy is required to bring it to a boil.  

<<The liquid may have been hot, but it was no closer to boiling when Stella removed the lid than it was when it was poured originally - >>

Sure it was - - because of the decrease in atmospheric pressure.

Q.E.D.  

[Michael Tee]

<<No MT, actually Amianthus is right, a stirofoam coffee cup cannot withstand enough pressure differential to cause the effect you are talking about, if you ever find one that seals at all you have found an unusual one .>>

You don't need a perfect seal for the heated gases inside to increase the atmospheric pressure.

<<If you were to place a bit of dry ice into a styrofoam cup and place a lid on it the CO2 would sublime and raise the pressure on the cups interior untill the lid would come off with a pop, this pop would represent less than one half of one LbPSI.>>

Meaningless test unless conducted on the actual cup and lid used by McDonalds and given to Stella.  Remember, plane, the debate was (on my side)  only about the theoretical possibility.  I had no idea how much pressure would be exerted on the lid from within.


<<Lets assume that when the cup was filled with hot coffe the liquid was ten degrees cooler than boiling, then the lid would be applied, a well designed lid will vent , but assumeing that the lid would not vent ,the sealed hot liquid and vapor would tend to develop a reduced pressure as it lost heat and the vapor condensed .>>

Again you're assuming without any factual basis that the liquid will lose heat faster than the vapor condenses.


<<I recall my mother canning tomato , beans , jelly etc.  The usual procedure is to bring the liquid in the jars up to a high tempreture and then apply a lid loosely , when the heat is removed the contraction of the vapor and air and the liquid within the jar causes the lid to pop down in a vacuum seal.>>

No one is denying the eventual result, plane, but that says nothing regarding how long the lid can stay in place while the gas mixture inside the cup is still hot.

<<There are a few things that can be done that seem like the effect that you are speaking of , but they canot be done with a coffee urn.>>


Check out what happens when you drop three "Mentos" into a two liter diet drink.

http://video.google.com/videoplay?docid=-1450915772177922792

<<Note that water holds almost no disolved gas at 190 degrees.>>

Dissolved gas was my error, but recall that I backtracked and the argument still works on the classical definition of boiling - - which is a simple change-of-state process depending for each liquid only on temperature and atmospheric pressure.

<<Water brought to the boiling point will not necessacerily boil if undisturbed. Then when it is disturbed it can boil suddenly.>>

Thanks for pointing that out - - another argument in favour of Stella.

http://www.snopes.com/science/microwave.asp


<<Note that this couldn't be done with a coffee urn .>>

I don't know about that but all of this was happening in a cup anyway.

[Xavier_Onassis]

The fact is that this old lady was burned becausae McDonald's failed to take proper precautions and give proper warnings, and they should pay. The effing laws of thermoeffingdynamics have nothing to do with the case.

On the other hand, drive-through food is idiotic. I never buy food at the drive-through. The odds of beihng overcharged or served the wrong thing are far too high to diddle with drive-through food.

Anyone who thinks they need drive-through coffee is too lazy to deserve any coffee.

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I have noticed that because people have slipped and fell on wet floors, nearly every dry floor in every public place in Florida has clusters of those annoying yellow "slippery when wet" signs scattered all over the place.

I slipped and fell at the Auto Show three years ago and had an aching back for about a week. I failed to sue the bastards. Last year they raised the parking fee from $5 to $10 and I wished I had.

The Law Firm of Cohen and Cohen was advertising every night on TV, and I guess I just coiuldn't decide which Cohen to call.

[Amianthus]

Sure it was - - because of the decrease in atmospheric pressure.

When did the atmospheric pressure decrease? Was there a sudden pressure drop between the inside of the McDonalds and the car?

[Michael Tee]

<<When did the atmospheric pressure decrease? Was there a sudden pressure drop between the inside of the McDonalds and the car?>>

No, the atmospheric pressure inside the cup dropped after the lid came off. 

[Amianthus]

No, the atmospheric pressure inside the cup dropped after the lid came off. 

Perhaps you want to re-evaluate your terms? "Atmospheric pressure" is pressure related to the atmosphere. "Partial pressure" or "vapor pressure" is the term you're looking for.

And when you release the lid holding in the vapor pressure, the pressure will only lower to atmospheric pressure - which is unchanged.

[Amianthus]

Thanks for pointing that out - - another argument in favour of Stella.

Not really. That can only be done with distilled water - any impurities prevent superheating from happening.

Unless you want to ammend your statement and claim that McDonalds handed her a cup of superheated distilled water instead of coffee?