Evaporation, Boiling, Freezing: A Dramatic Adventure
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Video Lecture 25 of 46
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Date Added: February 5, 2015

Lecture Description

Some very strange things are here encountered. Indeed - some of it borders on witchcraft! But this is how NATURE behaves - in strange and wonderful ways!

A. We boil some water in a flask. We drive out all the occluded
gases and air. We stopper the flask. We take away the heat
source. The water STOPS boiling. Now we put our hands on
the flask. Mirabile dictu: the water begins to boil again —
with NO heat being added. Indeed - what we are doing is
TAKING HEAT ENERGY AWAY! The mechanism? The hands
are cold for the flask. Some of the water vapour condenses. The
pressure in the flask is reduced. The water can boil at lower pressure at a lower temperature. Strange indeed! And we can continue this operation for all of an hour. Try it - you will be enchanted.

B. If this is all true then we can do an astonishing thing. We can reduce the pressure above some water under a bell-jar. The water
can boil at lower and lower pressure and thus at lower and lower
temperature AND - mark this: it can boil at so low a temperature that it freezes! Hard to believe. This scheme of things
is known as THE TRIPPLE POINT since the water is in three phases:
liquid - solid - vapour. It is as dramatic an adventure as one
can see.

C. And here is an adventure for the dining table: Some ice resides
in a glass of ice water. We supply the guest with a short piece of
string. PROBLEM: get out some ice using the string. HOW? Lay
the string on the ice - gently - pour on some table salt. Wait
a bit. The salt melts some ice - the water which results freezes
again. The string is fixed to the ice. Strange business!

D. And all the while we are doing these wonderful things we can re¬
turn to the flask of water and BOIL IT AGAIN by laying on the
hands!

Course Description

Demonstrations in Physics was an educational science series produced in Australia by ABC Television in 1969. The series was hosted by American scientist Julius Sumner Miller, who demonstrated experiments involving various disciplines in the world of physics. The series was also released in the United States under the title Science Demonstrations.

This program was a series of 45 shows (approximately 15 minutes each) on various topics in physics, organized into 3 units: Mechanics; Heat and Temperature / Toys; and Waves and Sound / Electricity and Magnetism.

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