Thermodynamics question

kojikun · Post by **kojikun** » 2003-01-14 11:49am

Is there an equation where you can find the required energy input in order to raise a material by a given number of degrees? Assuming, ofcourse, you know the specific heat and shit of the material etc.

Admiral Valdemar · Post by **Admiral Valdemar** » 2003-01-14 11:57am

kojikun wrote:Is there an equation where you can find the required energy input in order to raise a material by a given number of degrees? Assuming, ofcourse, you know the specific heat and shit of the material etc.

Yeah, but I haven't a clue what it is. Best ask someone like victorhadin if he posts here or Darth Wong, my physics knowledge has dwindled over the years somewhat in formulae terms.

Try Google first though.

Post by **Colonel Olrik** » 2003-01-14 12:07pm

kojikun wrote:Is there an equation where you can find the required energy input in order to raise a material by a given number of degrees? Assuming, ofcourse, you know the specific heat and shit of the material etc.

The procedure depends of the situation. The relation between temperature and the rate of increase of internal energy (in a solid) is very simple and given by

dE = ro*Cp*dT/dt

dE = energy variation
ro = density of the material
Cp= specific heat of the material
dT/dt = temperature variation / time

His Divine Shadow · Post by **His Divine Shadow** » 2003-01-14 02:31pm

You know, examples always help, maybe I could even make a calculator for it.

kheegster · Post by **kheegster** » 2003-01-14 03:15pm

Simple...

Q=m*C*theta (too lazy to type in the greek alphabet)

Q=heat input
m=mass of material
C=specific heat capacity of material
theta=change in temperature

If you know the mass and heat capacity of the material, as well as the temperature change required, just multiply them together, and you'll get your answer...

[EDIT]: This formulae only works well for solids and liquids which won't expand much on heating...if you want the formula for gases, it gets more complicated...

kojikun · Post by **kojikun** » 2003-01-14 05:49pm

kheegan, what is Q? i mean, what does heat input mean? change in internal energy??

kheegster · Post by **kheegster** » 2003-01-14 06:27pm

kojikun wrote:kheegan, what is Q? i mean, what does heat input mean? change in internal energy??

Q is heat input, i.e. the energy entering the material. For example, if you use a heating element of P watts to heat it up over a period of time t, the energy produced by the heating element is P*t joules, and this energy is transfered to the material. Hence, in this case, Q=P*t=m*c*theta. By conservation of energy, the heat input IS internal energy...whatever energy you put in goes into the material's internal energy. Again, this approximation is valid only for solids and liquids, since they are not subjected pressure and volume changes like gases. In the case of gases, Q does not necessarily go into the internal energy of the gas.

kojikun · Post by **kojikun** » 2003-01-14 08:20pm

ok so then for solids and liquids

Q/(mc) = θ

yes?

Post by **Darth Wong** » 2003-01-14 09:08pm

Keep in mind that specific heat is not constant. We usually approximate, or simpy use room-temperature specific heat; do not overestimate the accuracy of this type of calculation.

kojikun · Post by **kojikun** » 2003-01-14 09:30pm

oh yes i know that pressure changes specific heat great. i always thought it was funny how when youre at a higher altitude water takes longer to boil or something like that. LOL :p

the reason i was asking is because, say you have a stable wormhole (requiring no power input) with one mouth on the surface of a planet and the other mouth high above the planet. If you went in the ground entrance, youd come out at the top, and thus magically gain potential energy. Obviously you cant "get" energy from nowhere, so I figured maybe it would be extracted from kinetic/internal energy. So when you go to a higher altitude via a wormhole, you freeze solid

and if you go to a lower altitude, you exlpode. LOL

really the wormhole itself would probably gain or loose energy and such because theres a necessary amount required to open a wormhole. take too much energy, wormhole collapses, and you and it get turned into instant radiation

I figure that if a wormhole is opened, its exit mouth would form only in a spot with equal potential energy for any given mass as where its entrance mouth is.

Durandal · Post by **Durandal** » 2003-01-14 10:56pm

kojikun wrote:I figure that if a wormhole is opened, its exit mouth would form only in a spot with equal potential energy for any given mass as where its entrance mouth is.

Potential energy with respect to what? You've got potential energy with respect to the Sun, as well. Your gravitational potential energy is never exactly equal at two arbitrary positions.

The thing you have to remember about wormholes is that, to an external observer, it would appear to be in two places at once. Crossing the threshold of a wormhole wouldn't require any work per se, because according to the wormhole, you haven't changed location; it exists in both places. It's a bit difficult to explain and, quite frankly, way over my head.

kheegster · Post by **kheegster** » 2003-01-15 05:09am

Perhaps it should be noted that wormholes are still a theoretical concept...none have been observed yet...

StarDestroyer.Net BBS

Thermodynamics question

Thermodynamics question

Re: Thermodynamics question

Re: Thermodynamics question