Week 5- You can't win, You can't break even, and you can't get out of the game

http://www.google.com/url?q=http://popup.lala.com/popup/504684676488258962&ei=QlB4S8z5JJSwNpSFqJcP&sa=X&oi=music_play_track&resnum=1&ct=result&cd=2&ved=0CAoQ0wQoADAA&usg=AFQjCNEvLvu4GtwZmk9RIaLE_UX1bTyh2Q

The title expresses the 3 laws of thermodynamics.

You can't win.
The "can't win" law is that energy is neither create nor destroyed. This is the conservation of energy that we could initially and naively  be hopeful about. If someone did not  know about the second law, it would make them think that they could keep reusing the same energy. If someone tries to sell you a perpetual motion machine, keep your money in your pocket (even if that perpetual motion machine is a water fuel engine for your car.)

You can't break even
The big gotcha is the second law of "you can't break even". This is the law everyone would love to break. Here is where entropy steals your free lunch. Take the car example in the book. We take hydrocarbons that have energy in chemical bonds. We burn it causing little explosions in our engine. That explosion is coverting into kinetic energy.... the car moves. The burning has some waste heat. Heat is 2 things: radiant heat and the kinetic energy of molecules moving faster. Surrounding molecules are moving faster. As they move faster then bump into other molecules transmitting the heat (faster motion). It is sort of like a multi-dimensional billard game. The heat runs away in all directions never to be seen again. Radiant heat is also running away in all direction.  (Both are still energy but it is no longer useful, because it is randomized). One fast moving molecule distributed among millons of slow moving molecules cannot be harnessed. Ok but we still have the kinetic energy of the car, but on earth we lose that too. It is dissipated by friction of the tires on the surface and friction of the car body with air. Friction also turns into heat energy.

So what if we say this combustion is wasteful. It makes lots of heat. What if we could do something like our bodies, where we break chemical bonds in sugars to get energy without fast, hot combustion. Sorry; after useful chemical and mechanical energy is derived from the molecule, this energy is also eventually lost to heat energy . (otherwise you would not need to eat after you were full grown.)

Yes in machines, you can recycle a tiny percentage of this "waste" heat energy to derive some energy but only when the heat is concentrated. In that case, if you can move that concentrated heat from the hot area to a colder area or if you can use the heat to create expansion, you can extract some kinetic energy. HOWEVER, eventually the heat  will be dispersed and you can get no useful work from it. You cannot harvest random heat (1 hot molecule out of millions of colder one) to do work. You cannot derive work from disperse or random energy. And you cannot create non-random energy out of random energy without putting in more energy, which defeats the purpose of trying to get energy out of a system.


Physics for future presidents
For an excellent lecture on this topic, listen to lecture 2 of "Physics for Future Presidents"  http://webcast.berkeley.edu/media/common/media/ce0e2b00-c7c8-49de-bf13-15f4416a8674_opencast_audio_course_alldist.m4a

If you are interested in the entire series Physics for future Presidents lectures see
http://webcast.berkeley.edu/course_details_new.php?seriesid=2009-B-51905|2009-B-69390&semesterid=2009-B
On this page you can choose if you want audio for your ipod or video (with exciting demos) on your video ipod or computer. (Hopefully you have high speed internet with no RUP.

Look at this 2009 version not the 2010 version. Prior to 2010 this course was given by Dr Muller. He is the original designer of the Physics for Future Presidents course. This was voted the best class on the UCB campus.  For more information see: http://muller.lbl.gov/