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General Science / What freezes first, hot or cold water ?

« on: 13/03/2005 17:12:32 »

This is a continuation of the "ice cube" thread, but I started
a new thread because the old one does not belong to me.

I decided to do the hot/cold water freezing experiment myself.
The water samples were from my tap. GH = 187 ppm. KH = 68 ppm.
The cold sample was prepared first. 232 g of tap water was put
into a 1 pint Corningware dish. The hot water was boiled, then
232 g was poured into another 1 pint Corningware dish. Both
samples were carried to a chest freezer at -24 C, and placed
on a wire rack in the freezer. The first temperature reading
was taken at this time, which would have been about 5 minutes
after the boiling water was poured from the kettle.

Temperature data was taken after 20 minutes in the freezer,
with a type K thermocouple. After the surface ice became too
thick to poke the thermocouple wire into, I stopped measuring
that sample.

Temperature Data

• TIME __HOT T COLD T


• 00 min  66.0 C  16.8 C


• 20 min  23.1 C  06.1 C


• 30 min  14.7 C  03.4 C


• 40 min  09.3 C  01.0 C


• 50 min  04.5 C  00.7 C


• 60 min  01.8 C  00.7 C


• 72 min  00.8 C  00.8 C


• 82 min  00.8 C  thick ice

Freezing Observations

The cold sample had a thin layer of ice form at 40 minutes.
The hot sample had a thin layer of ice form at 60 minutes.

Post-freezing Mass

The cold sample contained 232 g of water.
The hot sample contained 215 g of water.

Conclusions

Hot water does not freeze faster than cold water, but it is
apparent why one could come to the opposite conclusion. First,
the volume of hot water needed to add 232 g to the Corningware
dish was noticably larger than the cold water. If one were using
a volume measurement, one would start with less hot water. Then
the hot water lost most of its heat in the first minutes of the
experiment, even before I could transfer the containers to the
freezer. Most of this heat loss was carried by evaporation, and
that showed up in the mass measurement of the frozen water. If
one were performing this experiment using a shallow pan, such
as an ice cube tray, that would cause a large amount of mass to be
lost to evaporation. The remaining hot water could freeze before
the more massive cold sample.

The observed freezing temperature of the cold sample was 0.8 C,
and the hot sample at 1.8 C. It is tempting to say that was caused
by loss of GH due to boiling in the hot sample, but my observation
intervals are too large to be sure.

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Physics, Astronomy & Cosmology / Have the Pioneer Spacecraft Discovered Dark Matter

« on: 30/12/2004 00:27:31 »

http://story.news.yahoo.com/news?tmpl=story&cid=2026&e=9&u=/latimests/gravitymayloseitspull

Tracking data from the Pioneer 10 and 11 spacecraft shows thay are slowing down faster than gravitational theory predicts. There have been many theories to explain it, but I think the best is that the mass of the solar system is greater than we think. The extra mass would be dark matter. I think it makes perfect sense, since large amounts of extra mass are present in the galaxies, some of it must be right here at home.

What do you think?

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Famous Scientists, Doctors and Inventors / Thomas Gold has died.

« on: 28/06/2004 21:04:35 »

Physics has lost one of its great. Thomas Gold, 84, died Tuesday of heart disease in Ithaca, NY. He was profesor emeritus of astronomy at Cornell University.

He was best known for the steady-state theory of the universe. That theory has fallen into obscurity, but his theory that pulsars were rotating neutron stars was proven correct. In the 1940s, Dr. Gold theorized that the inner ear hears tones using resonating hair cells. He was dismissed as a meddling outsider by the medical profession until the 1970s, when they were discovered.

He is survived by his wife, 4 daughters, and 6 grandchildren.

4

General Science / Why did a piece of sticky tape on the magnetic strip bring my card back to life?

« on: 12/06/2004 17:08:46 »

My wife has worn out the magnetic strip on her debit card. Now, I would have been perfectly happy if she had just stopped spending money, but noooo, she went to the bank for a new one. The guy at the bank put a piece of tape over the magnetic strip, and gave it back to her. Now it works again. Why would this be? I would have guessed that a larger space between the magnetic strip and the reading head would have made the induced signal weaker, and more difficult to read, not easier. What's your theory?

5

Physics, Astronomy & Cosmology / The dipole problem.

« on: 16/03/2004 02:57:51 »

The cosmic background radiation (CBR) has a dipole moment clearly measured to great precision. It corresponds to a blue-shift, and a matching, equal and opposite red-shift in the opposite direction. The only reasonable explanation is that this is a Doppler-shift caused by the earth's velocity with respect to the CBR of about 220 miles/sec., or 0.0012 c, if memory serves. The exact number is not the issue, just the fact that this is a rather pedestrian velocity by cosmological standards.

Now the cosmological principal states that observers in all parts of the universe should see the same universe when they look out at the sky.

When we look at distant galaxies, we see large recesional velocities, relativistic velocities, numbers on the order of 0.5 c.

What do astronomers on these distant galaxies see when they measure the CBR? The cosmological principal implies it should be a low number, on the order of 0.0012 c. I'm having some trouble understanding why this is true. I know that relativistic velocities add according to the special theory of relativity, but in that theory, if one train measured 0.0012 c velocity, relative to an embankment, and a second train measured 0.5 C relative to the first train, the second train would not measure 0.0012 c relative to the same embankment. This is more complicated, and involves general relativity, and expanding space issues.

If somebody knows of a paper that has treated this problem, I'd like to hear about it. Thanks.