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Physical Reasoning

Estimating Absolute Zero

Characterize the following:

The following experiment can be used to estimate absolute zero using household objects. Prepare a pot of boiling water and a pot of ice water. Take a graduated baby bottle and hold it (using tongs) in the boiling water. After a few minutes, when it has stopped bubbling, remove it and plunge it rapidly into the ice water. Water will then stream into the baby bottle through the nipple, as the gas contracts. (Actually, the nipple collapses: to allow the flow of water, you have to manipulate the nipple.) When the flow of water stops, the volume of the water that has entered the bottle may be measured by holding the bottle right-side up; the final volume of the gas at 0 degrees C may be measured by holding the bottle upside down. The initial volume of the gas at 100 degrees C is the sum of the final volume of the gas plus the volume of the water. By doing a linear extrapolation between these two values to the point where the volume of the gas would be zero, one can find the value of absolute zero.

What would happen: If the bottle is immersed only very briefly in the hot water? Or only very briefly in the cold water? If it is laid on top of the pots of water rather than immersed in them? If the bottle is left in the outside air a long time between being in the hot water and being in the ice water? If the bottle has an open end with no nipple? If the bottle has other holes besides this nipple? If the bottle is opaque? If you use containers with air at 100 degrees and 0 degrees rather than water? If the quantity of ice water in the second pot is very small? very large? or if the quantity of hot water in the first pot is very small or very large? If the bottle is coated with styrofoam? If the bottle is not graduated? Why is the following not a reasonable experiment: "Take a volume of gas in your hands; cool it; see how much it shrinks."

Contributed by Ernie Davis (, New York University, U.S.A. (18th September 1997)

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