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Video Lecture 26 of 46
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### Lecture Description

The subject is filled with DRAMA. NATURE is wonderful to contemplate.

A. We do an old classic - boil water in a tin can - stopper it up -
and the atmosphere does its stuff! Incredible really. I suppose I
have done this very adventure ten thousand times and it never fails
to stir me. What do we do? We condense the water vapour in the
can - the pressure is reduced - the atmosphere pushes the can in.
And - if we listen carefully we can hear the water boiling in the
can. Now try to pull out the stopper; it is fixed in very firmly.

B. We lodge a silver coin in a block of dry ice - solid CO2. And a
wonderful thing ensues. The coin oscillates and sings. Why? The
heat energy in the coin "melts" some of the dry ice. Gas arises.
This pushes the coin over to one side. Conduction is better on
closer contact and gas arises on this side. Silver is a good conductor. Moreover - the pitch of the note emitted gets higher as
the coin gets colder. Watch for this. We shall see more of this in
the demonstrations on sound as well as in the next adventures on
REALLY COLD STUFF.

C. For the housewife: To cook hamburgers fast cook 'em slowly! Why?
When cooked FAST they are likely to be burned on the outside. Carbon is a good thermal insulator. So the meat is burned on the outside but not cooked on the inside! Thus PHYSICS plays an important
role in the kitchen!

D. Does peeling onions make you cry? Solution: Chill them. The vapour pressure is lowered and they do not trouble you so much. Again
PHYSICS.

E. VISCOSITY: how easily - how readily - how swiftly - do things
FLOW? We have heard the phrase: As slow as cold molasses. So
the viscosity of liquids goes DOWN with rise in temperature. Just
what the oil in the crankcase of your car does. And so when you
pour cold molasses the "glubs" are slow and sluggish. When warm
they are faster.

F. A strange thing indeed! A very carefully designed copper sphere
- hollow - has a very special volume and a very special weight.
It has some lead or copper "shot" inside it to give it EXACTLY the
weight we wish. We put this sphere in a beaker of warm water.
IT SINKS. Add ice - cool the water - the sphere comes UP. OR - start again. Put this sphere in a beaker of COLD water. It floats. As time goes by the water warms up - as we say. And now the sphere sinks. WHY IS THIS? The density of water varies with its temperature.

G. We have discovered that the viscosity of liquids goes DOWN with
rise in temperature. How about the viscosity of gasses? Or gases?
Strangely enough the viscosity of gases goes UP with rise in temperature. And we show this with an un-symmetric T-tube. When the
matter is more fully explored and we know enough mathematics we
can prove all these things by Kinetic Theory arguments or by Quantum Mechanics.

As a closing adventure we play with the silver coin on the dry ice once again. This device has its historical origins in a mechanism called THE TREVELYAN ROCKER - which you might look up.

### 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.