Pseudonymph

Hey everybody...
quick question...I was taught in biology that the 2nd law of thermo states that energy becomes more useless as it is used, eventually to end up as heat(the most useless form of energy.)
I have heard a lot of debate about this...is what I learned true? or not?
For the record i'm NOT debating evolution or anything, I'm just curious to see if what I learned was BS or not. I just want some clarification on this...thanks!

Oolon Colluphid

That's not too far wrong (though I wonder why you learned it in biology, not physics! ). THe last time the 2LoT came up was in <a href="http://iidb.org/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=58&t=000265" target="_blank">this thread</a>, and I did a long post there which hopefully explains what you're asking.

Cheers, Oolon

Wizardry

You're basically right.

The only thing that I'd correct is that heat isn't entirely useless. As long as you have an unequal distribution of heat, work can still be done. In fact, many common machines (think air conditioning, heaters, internal combustion engines) are actually heat engines.

The Second Law of Thermodynamics addresses the distribution of heat as well when it says that the amount of energy available for work always decreases to nothing.

Other than that, you're not too far off.

Peace out.

liquid

The 2LoT is not rubbish, it is a very fundamental law to the science of thermodynamics that engineers like myself (and the odd scientist )use in all sorts of analysis.

I would be very careful though, because it seems from the way you have stated it that you don't have quite a clear idea of what it is. Don't worry - that is not uncommon, because one of the main properties it concerns, entropy, is essentially abstract.

There are several ways of stating the second law, and several corollaries (i.e. direct consequences), but they all equate to the same thing.

The entropy of an isolated system will always increase. The fact that we always get heat transfer to the surroundings for all actions is a physical consequence of that.

In a sense, heat is the most useless form of energy - you cannot obtain energy from a latent heat source. However, it can also be the most useful, when there is heat difference. Passing heat down a temperature gradient allows some to be 'diverted' through a heat engine (basically a machine) and some useful work to be done. Examples are combustion engines, powerplants, you.

Pseudonymph

Thanks everybody!
this makes much more sense to me now...
Just wanted to be sure I had my facts straight.
and you know...I've had other people ask me why I learned that In biology class and not physics. i dont know excpet that I learned it in biology AP in 11th grade(which is a college level class) then I learned it again in Advanced Bio in college.
I just wanted to make sure I wasnt being taught something that wasnt true...thanks again!