Clarification of Answer by
25 Nov 2006 18:56 PST
Hi Geoff, nice hearing from you
Let me finish the section 2) first,
then we will stick with non-relativistic mechanics,
with thermodynamics really.
re 2) mc^c
PBS has a nice presentation on the famous eq. (search term) mc2
How do physicists explain Einstein's equation to curious non-physicists?
Listen online by selecting Play All or choose individual clips below.
Listen offline by downloading clips,
they asked 10 physicists to explain - and explanations differ
not because it is an open question, but because in 3 minutes it is not
possible to explain
What is energy?
what is matter?
we talk about that a bit in:
Pure Energy...Yes or No?
Part of the differences is in treating expression 'nuclear energy'
differently. Formula E=Mc^2 covers all processes, all energy conversions,
chemical, nuclear, etc. But it more useful in nuclear and elementary
particles (annihilation of positron and electron) then in case of
chemical reaction. That's why people, even physicist, quote in the
nuclear and particle
physics is if it would be specific to those processes.
re 1) Carnot's formula applies to the heat engines.
It is very practical (Carnot was an engineer) and is clever
since it pioneered the use of Carnot cycle. There are many different
substances, steam-water, freon, etc which can be used to build a heat
engine. One can go and try different substances, hoping to Find most
'efficient one' . Carnot reasoning did show that WITH ANY substance,
efficiency is limited by his formula.
That was the beginning of Thermodynamics. Today it applies to all
energy conversions, from heat to nuclear.
Today's answer to your question is the 2nd law:
Best conversion process you can invent, is the one in which entropy
does not change ( an isentropic or quasi-stationer process).
All other processes have entropy going up, more or less, and so are
'less efficient' The formulas for entropy may be complex. Carnot's
is a simple formula which applies to heat engines.
Second law applies to all processes, all conversions.
Expression 'forms of energy' is not exactly defined.
'Wind energy' can be a category in itself, or it can be kinetic
and internal energy of atmosphere gases.
Here are few 'official' lists:
When you have a rock on a high platform , at height h, in gravity field g ..
it has potential energy m*g*h right?
You kick it down, before it hits, it has kinetic energy corresponding
to m*g*h .. nothing is lost, because entropy did not change.
After it hits, most energy is dissipated (not LOST!!) and entropy
increased. That increase depends on the properties of the rock and
floor, and can be calculated. That's how it is.