Heat Energy Transfer by Conduction 
Heat Energy Transfer by Conduction
by Prof. Miller
Video Lecture 22 of 46
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Date Added: February 5, 2015

Lecture Description

How do we get heat energy or thermal energy from one place to another? ANSWER: ONE of the mechanisms is CONDUCTION. In this mechanism energy only gets from here to there. That is - there is no transfer of heated stuff. Heat is applied to one end of a conductor - say - and the resulting higher agitation of the elemental parts is felt by collision along the conductor.

A. We do a classic experiment first done by Ben Franklin. A copper
rod and an iron rod are tightly joined at one end. The common
junction is placed in some hot STUFF - boiling oil - say - and
the remote ends are held in the hands. After a time we FEEL some¬
thing. And we feel it sooner - quicker - faster on the copper
rod. Copper has roughly ten times the thermal conductivity of iron.
It is also a better electrical conductor.

B. A metal rod and a wooden rod are smoothly fitted end-to-end.
Over the common junction we wrap a sheet of paper - tight.
We now hoW the system over a flame at the junction. And what
do we see? The paper is scorched where the wood is but not
where the metal is. REASON: the metal being a good conductor
takes the heat energy away before the paper has a chance to heat
up high enough to kindle.

C. We put a flame under a paper cup. The paper cup burns - as we
might expect! Now we fill another cup with water - still paper
- and we can boil the water in the paper cup without any injury
to the paper! Indeed - we can boil the water all away! MORAL: why not do all our cooking in paper pots?

D. A thermometer reads room temperature. We quickly immerse the
bulb in a vessel of HOT water. What do we see FIRST? Answer:
A DROP in the reading. And after a time the mercury column
climbs. Any why is the thermometer bulb cylindrical? To expose
greater surface for quicker response to mercury. Remember the
beautiful properties of spheres. Which is why raindrops are spher¬
ical. The energy of a system tends toward least.

E. A burning cigarette on a glass ashtray is likely to go out when the
hot end gets to the glass. Why? The glass conducts the heat away.

F. A burning cigarette on the edge of a wooden block? IT scorches
the wood. See B again.

G. A dinner table TRICK? Wedge a spoon and a fork together with a
match properly lodged and balance the whole thing on the edge of
a glass. Add to the dilemma by having another match uniquely
placed giving the idea that this second match is NECESSARY for
stability! Now we propose to light all the matches. What will
happen? Take a wager!

H. And how to bake BIG potatoes QUICK? Trivial - Watson -says Holmes: just lodge some big nails in them. The metal is a good conductor!

I. And how about a roast in the oven - a BIG one? With a bone in it the heat conduction is very rapid. And bone is a wonderful thing - very wonderful! A blood factory!

J. Is it not better to put your feet out of bed on to a deep matted rug rather than on to a bare floor? And remember: They are both at the same temperature - remember this. But the matted rug is a poor thermal conductor — which is to say - it is a good thermal insulator.

K. And when you touch the metal faucet it FEELS COLD. It is no colder than the table top!

L. A more formal demonstration can be done with a device having a metal hub - like the hub of a wheel - from which spokes emanate - and the spokes are different metals.

Thus we see in these various demonstrations how heat energy or thermal energy isCONducted from a place of higher temperature to a place of lower temperature - and there is no transfer of heated stuff.

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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