Archimedes' Principle
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### Lecture Description

If a body is submerged in a fluid - a liquid or a gas - the body is buoyed up -lifted up - by a force equal to the weight of the fluid displaced. This is the Classic Principle of Archimedes. We show an array of DEMONSTRATIONS bearing on this Principle.

A - We weigh a body on a spring scale. It weighs "so much" . We now
submerge it in a vessel of water. The scale reads less. How much less? We discover this with another demonstration.

B - We now submerge the body in a vessel so the displaced water runs out a spout. We weigh this water which ran out - which was "pushed" out by the body. And what does it weigh? It weighs EXACTLY the very loss in weight the body experienced when submerged. A wonderful thing.

C - So the water in a vessel pushes up on a body submerged in it. Proof: We push a glass into a tank of water. The glass has a hole in the bottom. The water gushes up through the hole.

D - We show a dramatic demonstration of Archimedes' Principle with THE BUCKET AND CYLINDER.

E - As we all know: some bodies sink in water; others float. When does a body float? When it displaces a weight of water equal to its own weight BEFORE it is completely submerged. Thus it is that some wood sinks - other wood floats.

F - Mercury is fantastic stuff! It is very dense. We all know that steel will sink in water. What will steel do in mercury? Answer: Steel will float in mercury.
We show some exciting things in the Life of Archimedes.
1 - A mosaic depicting his death at the hands of a Roman soldier at the
Siege of Syracuse.
2 - A monument to him showing his Burning Mirror.
3 - The classic discovery of the relationship between the volumes of a
cylinder - a sphere - a cone.
4 - A sphere circumscribed by a cylinder - which is what Archimedes wished to have put atop his tomb.

The Life and Work of Archimedes should be read by every student.

### 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.