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.
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.