Laws of Thermodynamics?

Show 40 post(s) from this thread on one page
Page 2 of 3 First 123 Last
• 09-08-2012, 10:45 AM
hearthman
energy conversion
Take for example your car's brakes. When your car is in motion, there is kinetic energy that must be dissipated to stop. When you apply the brakes, pads contact the rotors or drums creating friction, which causes them to heat up quickly. Air flowing over the brakes cools the brakes thus transferring the heat by convection and the car stops. Now, think about going down a mountain. You keep riding your brakes until they overheat. What happens? You can't stop and make the headlines.

Back in the '60s, there were a growing number of motor vehicle accidents from brake failures. The cause was traced to hub caps restricting the flow of cooling air and wheels without adequate air slots. Spoked wheels and those with big spaces can move a lot of air thus often improving braking. If you coat the brakes and wheels with mud, you may not be able to stop hard because the mud insulates the brakes keeping them hot instead of allowing cooling. I've had this happen many times when 4 wheeling.

Now, think about your rotors and drums. It used to be we turned them down on a lathe to extend their life. However, the amount of allowance you have is so marginal it usually is not worth it. Nowadays, the rotor is ususally replaced out of hand. Why? Because you need a minimum mass of metal to absorb heat from the friction of the brakes without distorting the metal, which would break contact causing failure. It takes a critical minimum mass of metal to stop a car.

Does this help?
• 09-08-2012, 11:15 AM
Greend88
I'll throw a loop for you guys. Ask yourself if energy can not be created then how did it become to be? Did the initial energy of the universe just pop out of nothing?
• 09-08-2012, 12:01 PM
hearthman
energy is the potential between atoms created by God caused by the polar charge of electrons or the lack thereof. This results in bonds between atoms that, when broken, releases energy to be used to form new compounds. When you burn a molecule of methane, the bonds between the CH4 and oxyen reform into carbon dioxide and water with the evolution of heat and light.
• 09-08-2012, 08:02 PM
R Mannino
Quote:

Originally Posted by Greend88
I'll throw a loop for you guys. Ask yourself if energy can not be created then how did it become to be? Did the initial energy of the universe just pop out of nothing?

The Law of Conservation of Matter and Energy states it can not be created or destroyed............no the mass of the universe is finite and the energy in it is also finite. The Law just proves we can manipulate it.

A tree on the forest floor releases the same amount of carbon dioxide if it is left to rot or if it is burned in a fire, the Law in action.
• 09-09-2012, 12:45 AM
hvacrmedic
Quote:

Originally Posted by Greend88
I'll throw a loop for you guys. Ask yourself if energy can not be created then how did it become to be? Did the initial energy of the universe just pop out of nothing?

Maybe energy doesn't exist at all? That would resolve the paradox wouldn't it. If it never was, then it didn't have to be created.

A perception of a thing is not neccesarily a property of the thing. Take color for instance. If we say that some object is red, then this only means that it reflects red light and absorbs all other visible frequencies of em waves. But...we are hardwired by evolution such that we instinctively think of the color of an object as an intrinsic element of the object itself--something it "has". In reality, color is just something we percieve, and doesn't belong to the object at all, being light of some wavelength emitted from a source external to the object. To complicate matters, the "color" of an object will also change with relative motion to the object (due to the Doppler Effect.) It's no different with energy.

Suppose you're stationed by the railroad track and you're watching a train pass by. You have good info that the mass of the train is X kg, and you measure its speed at Y m/s. You calculate it's KE as

kg(m/s)^2 or XY^2

which in this case turns out to be a rather large number. A passenger on the train however measures the speed of the train as exactly 0 m/s. He calculates that the KE of the train is zero. It has no kinetic energy from his frame of reference. It should be obvious then that the KE that you attributed to the train is not an intrinsic property of the train, but rather just a perception, like color, relating to your particular frame of reference.

The bottom line is that our mode of thinking is tailored by evolution toward survival, and along with that came an aptitude for engineering, but not so much an ability to understand the true nature of the building blocks that we stack together. Anything beyond the engineering value of our physics is pure philosophy, which should be avoided for the sake of sanity (unless you're only speculating for personal amusement, or maybe for profit). Physics beyond the math is also called metaphysics.

I apologize for getting carried away with this. I've had this discussion with real physicists many times. The ideas above are not mine, just ideas that I was finally forced to accept.

What does this have to do with hvac anyway. ;)
• 09-09-2012, 08:42 AM
Saturatedpsi
Quote:

Originally Posted by hvacrmedic
What does this have to do with hvac anyway?

Thank you.:grin2:
• 09-09-2012, 09:44 AM
hydra
My brain hurts! Excellent explanations though.
• 09-14-2012, 11:12 PM
JNXMN
it's actually referring to energy, heat is just one form of energy.
• 09-15-2012, 10:09 AM
mgenius33
Quote:

Originally Posted by gregscott
So, can you think of anything that does not require the transfer of heat?

A form of energy that doesn't require the transfer of heat?
Potential Energy...
• 09-15-2012, 10:19 AM
mgenius33
Quote:

Originally Posted by hvacrmedic

Suppose you're stationed by the railroad track and you're watching a train pass by. You have good info that the mass of the train is X kg, and you measure its speed at Y m/s. You calculate it's KE as

kg(m/s)^2 or XY^2isn't this the formula for Force=ma, KE= 1/2mv^2

which in this case turns out to be a rather large number. A passenger on the train however measures the speed of the train as exactly 0 m/s. He calculates that the KE of the train is zero. It has no kinetic energy from his frame of reference. It should be obvious then that the KE that you attributed to the train is not an intrinsic property of the train, but rather just a perception, like color, relating to your particular frame of reference.

Sounds like we are touching on Einstein's theory, and Socrate's statement noted in my signature...
• 09-15-2012, 10:57 AM
hvacrmedic
Quote:

Originally Posted by mgenius33

Sounds like we are touching on Einstein's theory, and Socrate's statement noted in my signature...

I borrowed his train and referred to relavity of motion, but I wasn't necessarily referring to any of Einstien's original hypotheses, and don't in general subscribe to his version of relativity. The question here is whether energy can be created from nothing, and that's a question that's outside the realm of physics. It may even be a meaningless question.
• 09-15-2012, 12:23 PM
JBM1000
To even measure absolute zero or below takes a transfer of energy be it a crossover of dimensions of the 4th kind or staying inside our tiny barely able to compute reality. "That is one of my better lines of pure B.S. I must admit"!
• 09-15-2012, 06:38 PM
Andy Schoen
Quote:

Originally Posted by hvacrmedic
Maybe energy doesn't exist at all? That would resolve the paradox wouldn't it. If it never was, then it didn't have to be created.

Or perhaps more correctly, the total sum of energy in the universe is zero. http://en.wikipedia.org/wiki/Zero-energy_universe

No need to figure out where energy came from. And the First Law still applies. ;)
Show 40 post(s) from this thread on one page
Page 2 of 3 First 123 Last