ROANOKE TIMES
Copyright (c) 1995, Roanoke Times
DATE: Tuesday, December 26, 1995 TAG: 9512260025
SECTION: VIRGINIA PAGE: C-1 EDITION: METRO
COLUMN: What's on your mind?
SOURCE: RAY REED
Q: I have a bet with a friend that hot water freezes faster than cold water. Who's right?
S.F., Buena Vista
A: Depends on the specifics of your bet. Did you mean hot water freezes solid first, or did you mean it's first to show ice on the surface?
The freezing rate can be demonstrated by this experiment, as outlined by Roanoke College physics Professor Robert Hudson.
Take two pie pans of the same size. Fill one with water cooled to about 50 degrees. Fill the other pan with water heated almost to boiling, say 200 degrees.
Put the pans in a freezer at the same time.
The pan of cold water will form a skim of ice first.
The hot water, though, will be first to freeze solid.
Here's why: The hot water will cool rapidly, evaporating all the while. By the time it falls to 32 degrees, there will be less water in the pan.
The evaporated portion of the pan's contents will be frost on the walls of the freezer. (Or, in the case of a frost-free model, water vapor blown out of the freezer.)
The hot water will reach a solid state first because less of it stayed in the pan to freeze.
Here's another possible condition: If both pans are covered, the cold water freezes solid first. The hot water, with no place to release its vapor, retains its mass and takes longer to reach 32 degrees.
Hudson said local plumbers have told him hot-water pipes can freeze before the cold lines.
This may happen because the heating process drives out dissolved substances in the water, Hudson said.
These substances can function as antifreeze, possibly lowering the water's freezing point a degree or so.
A water heater may drive out gases such as oxygen, and cause other matter to settle to the bottom of the tank.
With the dissolved substances gone, stationary water in a hot line could freeze first, Hudson figures.
But that's a theory, not a scientific experiment.
Q: Can you print an address so we can send a card or letter to servicemen and servicewomen in Bosnia?
K.D., Roanoke
A: The Army hasn't yet established a general address for Bosnia, but here's one to use in the meantime:
Any Soldier Mail
Operation Determined Effort
APO A E 09135
This zip code encompasses all of Europe and was established years ago so troops could receive holiday mail.
Soldiers deployed to Bosnia, and their families, have been given an APO zip code.
An Army spokesman said only about 1,000 U.S. troops have reached Bosnia, and Operation Determined Effort is still being set up.
While mail is a high priority, it won't be organized until the basic essentials are in place.
The Army expects to establish a zip code for Bosnia sometime after Jan.1.|
Got a question about something that might affect other people, too? Something you've come across and wondered about? Give us a call at 981-3118. Maybe we can find the answer.
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