Pascal's Principle: The Properties of Liquids 
Pascal's Principle: The Properties of Liquids
by Prof. Miller
Video Lecture 14 of 46
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Date Added: February 5, 2015

Lecture Description

MATTER as we know it exists in three familiar "states": Solid-Liquid-Gas. Liquids have strange and wonderful properties one of these being incompressibiiity - they cannot be squeezed together very much. We show this enchanting business in a number of DEMONSTRATIONS.

A - PASCAL'S PARADOX: Three glass vessels have different shapes but the same base. We fill these to the same depth with water. And very strangely they have the same pressure on the bottom and the same force on the bottom. Pressure we define as a Force per unit area - that is
P = F/A.

B - The Hydraulic Press utilizes the dramatic property of the incompressibiiity of liquids and Pascal's Principle which says: A force communicated to a liquid is "felt" without loss in all parts of the liquid. The press is worked by a lever so this machine is a Compound Machine and it has enormous Mechanical Advantage.

C - A hypodermic needle has a very tiny point - a point of small area. If we push the piston with the thumb with a force say of ONE pound and the point has an area of ONE THOUSANDTH of a square inch we have at the point end a PRESSURE of ONE THOUSAND POUNDS PER SQUARE INCH. No wonder the needle goes in!

D - We show an array of demonstrations of a simple ordinary sort which point up the beauty of these properties of liquids:
1 - We squeeze a flask equipped with a glass tube; the liquid goes UP
and it goes DOWN. The glass is highly ELASTIC and the water is highly incompressible.
2 - The Cartesian Diver: The water is incompressible; the air IN the
Diver very compressible.
3 - A flask filled COMPLETELY with water can be broken apart by a
sharp blow on the stopper. WHY? The water is incompressible.
4 - A flask filled COMPLETELY with water can be used as a hammer
to drive nails. WHY? The water is highly incompressible.

E - A tin can is filled with water. The can has a TINY hole in the side near the bottom. With the stopper IN the water does not run out! Pull out the stopper and the water runs out! What holds the water IN? Answer: Atmospheric Pressure.

F - A U-Tube has mercury in it to a certain level. We add water to one arm. The mercury falls in that arm and rises in the other. A measure of the mercury and water columns reveals a wonderful thing: The ratio comes out to be 13.6 - which is the specific gravity of mercury.

We show a picture of Blaise Pascal - that genius of the 17th century who lived a very short life (1623-1662) but one filled with drama. He died as is said -with seven-fold immortality: as a mathematician - a physicist - an inventor -chief creator of his nation's great prose - a theologian - a philosopher - and a fanatic. His sister wrote a biography of him.

Course Index

  1. The Idea of the Center of Gravity
  2. Newton's First Law of Motion: Inertia
  3. Newton's Second Law of Motion: The Elevator Problem
  4. Newton's Third Law of Motion: Momentum
  5. Energy and Momentum
  6. Concerning Falling Bodies & Projectiles
  7. The Simple Pendulum and Other Oscillating Things
  8. Adventures with Bernoulli: Bernoulli's Principle
  9. Soap Bubbles and Soap Films
  10. Atmospheric Pressure
  11. Centrifugal Force and Other Strange Matters
  12. The Strange Behavior of Rolling Things
  13. Archimedes' Principle
  14. Pascal's Principle: The Properties of Liquids
  15. Levers, Inclines Planes, Geared-wheels and Other Machines
  16. The Ideas of Heat and Temperature
  17. Thermometric Properties and Processes
  18. How to Produce Heat Energy
  19. Thermal Expansion of Stuff: Solids
  20. Thermal Expansion of Stuff: Gases & Liquids
  21. The Strange Thermal Behavior of Ice and Water
  22. Heat Energy Transfer by Conduction
  23. Heat Energy Transfer by Convection
  24. Heat Energy Transfer by Radiation
  25. Evaporation, Boiling, Freezing: A Dramatic Adventure
  26. Miscellaneous Adventures in Heat
  27. The Drama in Real Cold Stuff: Liquid Nitrogen
  28. The Physics of Toys: Mechanical
  29. The Physics of Toys: Acoustic and Thermal
  30. Waves: Kinds of Properties
  31. Sound Waves: Sources of Sound & Pitch and Frequency
  32. Vibrating Bars and Strings: The Phenomenon of Beats
  33. Resonance: Forced Vibrations
  34. Sounding Pipes
  35. Vibrating Rods and Plates
  36. Miscellaneous Adventures in Sound
  37. Electrostatic Phenomena: Foundations of Electricity
  38. Electrostatic Toys, Part 1
  39. Electrostatic Toys, Part 2
  40. Adventures with Electric Charges
  41. Adventures in Magnetism
  42. Ways to "Produce" Electricity
  43. Properties and Effects of Electric Currents
  44. Adventures in Electromagnetism
  45. Further Adventures in Electromagnetism
  46. Miscellaneous and Wondrous Things in E&M

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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