- #1

eneacasucci

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- TL;DR Summary
- Variation of air temperature with altitude, considering the approximation of perfect gas, which transformation explains this phenomena?

Considering the approximation of perfect gas, I don't understand why at higher altitude the temperature is lower.

Intuitively it is clear to me, but I do not understand the kind of transformation that takes place; the gas is free to expand and the pressure too is not constant, since it decreases at higher altitudes. Then also the temperature decreases but I don't understand if we can see this decrease of temperature from this formula PV=nRT or if it is an isothermal transformation so the temperature of a certain mole of gas doesn't change due to the free expansion but for other mechanisms of heat transfer (like conduction and convection).

I've also tried to think about the ocean, when we go deeper the pressure increases but there is a liquid, and a liquid is not compressible, so the pressure there is not associated to a change in temperature, which is due mainly to convective motion.

Intuitively it is clear to me, but I do not understand the kind of transformation that takes place; the gas is free to expand and the pressure too is not constant, since it decreases at higher altitudes. Then also the temperature decreases but I don't understand if we can see this decrease of temperature from this formula PV=nRT or if it is an isothermal transformation so the temperature of a certain mole of gas doesn't change due to the free expansion but for other mechanisms of heat transfer (like conduction and convection).

I've also tried to think about the ocean, when we go deeper the pressure increases but there is a liquid, and a liquid is not compressible, so the pressure there is not associated to a change in temperature, which is due mainly to convective motion.