Quick trick!

Classical Mechanics Level 1

What is the driest area in your house?

The living room The fridge The bathroom The oven The balcony

1 solution

Prasun Kumar
Dec 22, 2015

Clearly, it can't be the bathroom. It can't be balcony as it get moistured by dew. Neither could be the living room since humans moisten it by respiration. It can't be the oven because water is vaporized from the food inside it. So it is the fridge which is the driest because it condenses all the humidity inside it.

There is some ambiguity to this solution. In terms of the relative humidity, the inside of the fridge may be very near 100% RH. Where as the RH of a heating oven may be close to 0% RH. In terms of total amount of water vapor held in a volume of air your solution may be correct in terms of the ratio of water in the air relative to the maximum holding capacity of that volume your solution is not correct.

My point is most of the time when a reference is made to how dry air is, it is relative humidity level that is the used to describe or measure the dryness not total volume of vapor in the air. It is far more common, in fact routine, to refer to dryness of air in terms of RH and not the absolute water vapour held in the air. Dryness of air is almost always a reference to as RH%. Try to find a weather report or reference to the dryness of the air in a living space, which is typically measured using a humidistat, that is quoted in terms of absolute water vapor, it is always RH.

Why should anyone assume that in this question "most dry" (an ambiguous term) is a reference to anything but the typical and commonly used meaning, when describing the dryness of air.

So I completely disagree with your solution.

Darryl Dennis - 5 years, 5 months ago

Well I just spilled water all over my fridge. now the jokes on you.

Michael Livanos - 5 years, 5 months ago

Nice explanation! Thank you!

Noel Lo - 5 years, 5 months ago

Its certainly the fridge because vapor cool down and turn into ice! I wander why did you use the "Exclusion" principle

jafar badour - 5 years, 5 months ago

Just to remove any doubts about the other options!

Prasun Kumar - 5 years, 5 months ago

Using your definition of "most dry" which is of these location would you consider most dry today? The current temperature outside on my open deck today is -12.1 degrees C. the relative humidity outside today is 91%. The dew point is -13° C. The temperature in my living room is 19° C with a relative humidity of 32%. These are the actual conditions here this morning.

If the temperature in my frig is 4° C are you saying that you believe that the inside of my fridge it will be the "most dry" when compared to the other two location no matter what the RH value is there? Have you any legitimate reason to say this? What do you mean by most dry?

You certainly did not remove any doubts about the other options.

Darryl Dennis - 5 years, 5 months ago

@Darryl Dennis – -13 the temperature out side your house >>> so weird , here In Syria It never goes under 2degree in the coldest winter night

jafar badour - 5 years, 5 months ago

@Jafar Badour – Well! I realize that the weather here, where I live, in western Canada may not be typical for most of the densely populated areas of the planet. But it is far from unique. I have experienced -50° C. Temperatures of -40° C will be a occur several times every winter. We typically experience more then four months each year where, if the outdoor temperature gets up as high as +5° C even for a few hours, that would be considered very pleasant and mild conditions. There is still moisture in the air even at extreme temperatures. The notion that all the moisture will condenses out of the air or turn to ice at refrigerator temperatures is simply incorrect. The water vapor holding capacity is very low compare to room temperatures but without a RH value no one can make any meaningful statement about "most dry".

I am only pointing this out because part of the point of this entire Brilliant site is to foster an understanding of basic principles in the math's and sciences. In my opinion the accepted answer and certainly the explanations for that answer actually may lead to some very incorrect ideas about how moisture is held in a air mass.

The solution to the question is, at best, unclear because of the ambiguity of the term "most dry" or simply wrong if we use the commonly accepted and widely used RH% value to define how dry air is.

I do not mean to be overly fussy or argumentative. I am simply attempting to clarify the principles of moisture in air and point out that it is not a simple mater of how warm the air is.

Darryl Dennis - 5 years, 5 months ago

@Darryl Dennis – Sir, I agree with you. I didn't consider the RH value. So, my solution is flawed. I just tried to get away with a casual solution. Next time , I will consider all the technical details. Thanks for your remarks .

Prasun Kumar - 5 years, 5 months ago

Quick trick!

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