Heat Energy Transfer by Convection 
Heat Energy Transfer by Convection
by Prof. Miller
Video Lecture 23 of 46
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Date Added: February 5, 2015

Lecture Description

In this mechanism of heat energy transfer there is an actual motion of heated stuff - a motion which results from differences in density and by the action of gravity. A look at the Latin origins of the words conduction and convection will make their meanings clearer. So - as I like to say - knowing Latin - and Greek - is good for knowing Physics!

A. We show two smoke stacks in a glass-walled box. Under one stack
is a lighted candle. By observing the behavior of smoke in the box
we see clearly the flow of heated stuff. Thus we see too why it is
that huge smoke stacks have such a good "draft:. And - strangely
enough - we learn that "wet" air is lighter than dry air. Which
is NOT what we might first think!

B. In a framework holding water which we color a bit with food dye
we see how great the convection forces due to change in density.
Thus in A and in B we encounter convection in FLUIDS - the
generic name for liquids and gases. We have an actual transfer
of STUFF. ~

C. A candle resides in a dish. We bring down over the burning candle a glass cylinder. In a short time the candle flame must certainly
"expire" - the flame is wanting air to breathe. Now we introduce a partition which provides TWO channels - one for the cold
air to fall down into - and another for the hot air to come up.
Remember: it is not good to say that HOT AIR RISES. Nothing
can RISE! It must be pushed up.

D. We show more of DEMONSTRATION L in LESSON 7 - with a
wheel equipped with hub and spokes. An interesting inquiry a-
rises: TWO bars are of the same stuff - iron - but one is twice the
diameter of the other. So some geometry Js necessary. Double
d - we make A four times. We make S - the surface twice as much. So although conductivity is made four times greater the heat loss due to radiation is doubled. Hence the net gain is only twice.

E. A "gag" can be done with a clean silver coin and a handkerchief.
But be careful. The fit must be tight and the coin clean or you'll
end up with a hole in the handkerchief.

F. Since the action of the mercury column in a mercury-in-glass thermometer is not too easily seen we can witness things better by fitting up a "whiskey" flask with a stopper and glass tube. And a bit of color in the water gives the matter some prettiness. Now immerse the flask in hot water. What do we see FIRST? The column FALLS!

The mechanisms of conduction and convection constitute TWO important actions for the transfer of thermal energy. For these we need some STUFF. The question arises: How can heat energy get from place to place with nothing in between?

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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