Critical Thinking 101

[ArcticDiver]

The ability to sift facts and arrive at a correct solution is a basic skill in scuba diving. So, I thought this conversation which was overheard on my flight from the Mainland to Hawaii would provide some grist for the analytical grinder. For what it is worth the airplane was a nearly new B-767-300.


Diver? A (at about half way across the pond): Boy if it wasn't for burning so much fuel this airplane would be heavier when we land in Honolulu that when we left Los Angeles.
Diver? B: Why do you say that?
Diver? A: Have you seen all the people using the lavatories? They must have peed gallons, and gallons. That is all going into the holding tanks. You know they don't drain them overboard in flight any more.
Diver? B: No you ninnie; the airplane will be lighter. In addition to the fuel burned those people now have lighter bladders. And, have you seen the passsengers chowing down? The galley must be empty by now.
Diver? A: Of course, you are right, I should have known. The airplane will be lighter! You always were smarter than me.

So; what say you: Lighter? Heavier? Why?





Who is correct?

 

[H2Andy]

lighter, of course

no weight is added to the plane while en route*, and tons of weight is removed by burning fuel


*--assuming no icing

 

[apemb]

Lighter because less fuel. All fecal matter, urine, food, and water is the same on landing as it was on take-off. The only difference in the flight is fuel weight.

Final answer is Lighter!!

 

[MXGratefulDiver]

Depends on whether more people are peeing ... which weighs the plane down ... or farting ... which buoys the plane up. Overall, it's probably a wash ...



... Bob (Grateful Diver)

 

[JahJahwarrior]

Should be lighter. All the food that goes through the body has the same mass as it did before it went through the body.

Even if there was some icing, since the pressure is lower and the temperature is lower, the density of the ice would be lower than that of water (if the pressur ewas very very very high, as in millions of atmospheres, then you could have ice denser than water...but that stuff is just freaky), jet A fuel weighs about 6.8 pounds per gallon, 1 gallon of water at room temperatur eis about 8 pounds. You could figure out how much water would have to freeze on the wings for the weight to be equal, based on how much fuel is burned, but that is relatively moot since most planes have ways to deice the wings, so ice buildup isminimal. And if the plane lost altitude, temperature would rise and so would pressure, so ice would begin to melt.

Both divers need to redo their OW course, I have a feeling they don't understand gasses or partial pressures very well, if they can't do simple subtraction.

 

[jeckyll]

OMG, how could the plane possibly get heavier. The doors are closed aren't they? No way to get anything more onboard.

Do the lavatories vent to the atmosphere? In that case you have an one way weight reducing function.



If the lavatories do were not discharging anything, then the thing is exactly the same weight except for fuel.

 

[WesTexDiver]

Lighter...food being metabolised and turned into heat energy that well weighs nothing. Burning calories = weight loss regardless of how little.

 

[Thalassamania]

Forgetting about fuel for the moment, as one respires carbohydrates are changed to Carbon Dioxide (which is exhaled) and water (which is exhaled and excreted). Substantial water is also lost to the very dry. All that is exhaled is ultimately lost thought the ventilation system, so the plane is lighter.

 

[AXL72]

post a tougher one

 

[ItsBruce]

Funny that you are talking about airplane weight, but I've got a corollary question:

Assume an airplane is sitting on an infinately accurate scale. Assume that the door is open and a bird flies into the plane but does not land while inside. Does the weight, as measured by the infinately accurate scale, increase or decrease?