Most of the stuff in Nature expands when heated. And we have some wonderful and exciting demonstrations of this. In some cases some enchanting questions arise
A. The classical ball-and-ring demonstration: We have a metal ring
- brass - and a metal sphere - also brass. At room temperature we show that the ball does not go through the ring. So we say the ring is too small OR the ball is too big! Now we heat the ring and presto - the ball now goes through. We say the ring got bigger OR the hole got bigger! We must UNDERSTAND exactly what is going on here!
B. We now have some metal plates - round ones - square ones -
rectangular ones - and in each is a hole - a tiny tiny hole in
some. Now we heat these plates uniformly - as we could do in
an oven - and we ask: What does the tiny hole do? There are
only three cases: The hole does nothing.
The hole gets smaller.
The hole gets bigger. And I leave it as an enchanting exercise for you all to contemplate! I might give a HINT: The ring which we first used in the ball-and-ring demonstration is really a plate with a big hole! Got it now?
C. We have a metal ring - no need to say EXACTLY CIRCULAR. And
this ring has a diameter of its own stuff. We now heat this ring uniformly - as in the oven of my stove. Question: does the ring preserve its circularity or does it warp? Good question! Suggestion!
Those of you who think one thing should try to convince those who
think another! This is real intellectual inquiry.
D. A bimetallic strip consists of two metals fixed to each other along
their length. We heat the strip. Let us say one metal is iron -
the other brass. We see the strip bend. Question: does it bend
toward the iron or toward the brass.
A question for mathematical proof: If both strips are of equal thickness d the straight bimetallic strip will bend into a circle
E. We have two rods - both look like glass. One - we say - IS
glass; the other is quartz. We heat these to red-hot in a flame.
NOTE: while heating we see a color in the flame. Color is a
thermometric process. Then we immerse them both in a beaker of
COLD water. The glass shatters. The quartz does not. The quartz
has a very small temperature coefficient of expansion.
F. We introduce an interesting question: Consider one rail of the RR
track between Los Angeles and San Francisco. Let it be 400 miles
long - in one continuous strip. No breaks. Let this rail suffer an
overall change in temperature of - say 25°C. QUESTION: How
much expansion does this 400-mile rail suffer? ANSWER: Nearly
600 feet! Hard to believe but easy to prove:
G. Why does popcorn pop? A kernel of un-popped corn looks dry -
lifeless - inert - dead! But it is not dry! and it is not dead!
When we heat it the very tiny - very minute - bit of water which
is in it EXPANDS enormously - some 1700 times! The forces are
staggering!
