Atmospheric Pressure 
Atmospheric Pressure
by Prof. Miller
Video Lecture 10 of 46
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Date Added: February 5, 2015

Lecture Description

Put out your open hand - grab hold of a handful of air - there is NOTHING there! Or so it seems! But there is - there's a powerful lot of STUFF there -an enormous array of it! The ATMOSPHERE is a massive thing. The pressure of the air is about 15 pounds per square inch at sea level. On every square inch of everything there is a load of 15 pounds - very nearly. The average human being bears a load of some TWENTY TONS! The whole blanket of atmosphere which envelops the Earth weighs some 5000 million million tons! Fantastic! We show an array of enchanting DEMONSTRATIONS on THE PUSH OF THE AIR.

A - We boil water in a tin can. We drive out all the air. We now stopper up the can. The water vapor in the can condenses - that is - it goes back into the liquid state. The pressure in the can is reduced. The atmosphere squeezes the can! The PUSH of the air is terrific.

B - We do the same thing with another can but in this case we evacuate
the can - we take out SOME of the air - with a vacuum pump. Again the great push of the air squeezes the can.

C - A funnel has its open end covered with a stout rubber sheet. We take out some of the air. The atmosphere PUSHES the sheet in — the more air we take out the more it pushes in - and suddenly BANG - the sheet is burst apart by the PUSH of the air.

D - "Suction" cups! This is bad language! There is NO SUCTION! We
squeeze the "suction" cups together; we drive out the air between them. Then what? The atmosphere OUTSIDE pushes them together! And very strongly.

E - We do the classic experiment of Otto von Guericke with the Magdeburg Hemispheres. In the original demonstration in the Public Square SIXTEEN HORSES pulled the hemispheres apart. But only eight were really necessary. See why?

F - On a sheet of newspaper about 20" by 30" - that is - on an area of 600 square inches - there rests a load of atmosphere of some 9000 pounds. Fantastic! Now we wish to put this enormous load - this massive MASS - into motion by a short-lived impulsive blow. Remember the Sack of Bricks in Inertia? Newton said: "A body at rest wishes to remain at rest". And 9000 pounds - over FOUR TONS - has just too much inertia to be put into motion suddenly. So BANG! The board is broken because the great load of air does not wish to move.
When the air is quiet the PUSH of the air is something to think about. Imagine what happens when this massive air is on the move - as in a hurricane or in a tornado. Cities are destroyed!

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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