22 Sep 07
2 edits
Originally posted by coquetteThat's partially correct - but do evening breezes typically go country to city or city to country? Why?
Since the specific heat of concrete is higher than soil, the average temperature of the city is higher because solar radiation has heated both the sol and the concrete, but the concrete has much more energy stored and radiates it back longer as the evening air cools..
Here's the question again. While there are numerous of reasons why the city is warmer, explain why using just this fact.
11. Concrete has a higher specific heat than soil. Use this fact to (partially) explain why a city has a higher average temperature than the countryside around it. Would you expect the evening breezes to blow from city to country, or country to city? Explain.
22 Sep 07
Originally posted by Ramnedsecond part about the direction of the breezes was answered earlier .. evening breezes would head in toward the warmer city due to air rise and drawing cooler air in along the ground level into the city.
That's partially correct - but do evening breezes typically go country to city or city to country? Why?
Here's the question again. While there are numerous of reasons why the city is warmer, explain why using just this fact.
[b]11. Concrete has a higher specific heat than soil. Use this fact to (partially) explain why a city has a higher average tempe ...[text shortened]... you expect the evening breezes to blow from city to country, or country to city? Explain.[/b]
22 Sep 07
Laws of Thermodynamics
12. Imagine a gas in an insulated cyclinder with a movable piston. The piston has been pushed inward, compressing gas, and is now released. As the molecules of the gas strike the piston, they move it outward. From the point of view of energy principles, explain how this expansion causes the temperature of the gas to drop.
22 Sep 07
Originally posted by Ramnedexpanding gases cool because temperature is really an energy measurement of the mass X velocity of the gas molecules hitting against an object, transferring energy to that object . . .the object might a thermometer. The mass remains the same, but the expanding chamber spreads the molecules out so that there are fewer collisions with each other, and the measuring object or other objects. fewer collisions means lesser energy to transfer, lower temperature.
Laws of Thermodynamics
[b]12. Imagine a gas in an insulated cyclinder with a movable piston. The piston has been pushed inward, compressing gas, and is now released. As the molecules of the gas strike the piston, they move it outward. From the point of view of energy principles, explain how this expansion causes the temperature of the gas to drop.[/b]
22 Sep 07
Originally posted by coquetteNo...how do the molecules in question interact with the piston?
expanding gases cool because temperature is really an energy measurement of the mass X velocity of the gas molecules hitting against an object, transferring energy to that object . . .the object might a thermometer. The mass remains the same, but the expanding chamber spreads the molecules out so that there are fewer collisions with each other, and the meas ...[text shortened]... ng object or other objects. fewer collisions means lesser energy to transfer, lower temperature.
22 Sep 07
i dont understand your follow up. the question is about the temperature of the gas. the interaction of the gas molecules with the piston is the same as with the other walls of the chamber, the fact that the piston is moving is incidental, exept that it's where the energy is "going" . .but that's not about the "temperature"
22 Sep 07
2 edits
Originally posted by coquetteBut what is the interaction of the molecules with the piston? This is important because it causes ....
i dont understand your follow up. the question is about the temperature of the gas. the interaction of the gas molecules with the piston is the same as with the other walls of the chamber, the fact that the piston is moving is incidental, exept that it's where the energy is "going" . .but that's not about the "temperature"
That's what I'm looking for. Yes, the question is about the temperature of the gas, but from the point of view of the energy principles....what are the molecules doing to the piston? What is this called? What does it cause to the temperature?
That's about all the info I can give without giving the proper answer. You need to answer from the POV of the energy principles as the question directs, I don't think you are quite doing that...basically answer the questions in this post...
22 Sep 07
Originally posted by RamnedWhat you want us to say is that the molecules are transfering their momenta to the piston while colliding with it. And by doing that they're losing kinetic energy.
But what is the interaction of the molecules with the piston? This is important because it causes ....
That's what I'm looking for. Yes, the question is about the temperature of the gas, but from the point of view of the energy principles....what are the molecules doing to the piston? What is this called? What does it cause to the temperature?
That's ...[text shortened]... cts, I don't think you are quite doing that...basically answer the questions in this post...
Now, temperature is just the macroscopic measure of how fast the molecules of the gas are moving. The faster they move the hotter the gas. So, if the molecules are moving with an average lower speed the gas temperature decreases.
This was a good question btw. The kind of question I like to answer in physics.
22 Sep 07
Originally posted by coquetteI think that in this post :"expanding gases cool because temperature is really an energy measurement of the mass X velocity of the gas molecules hitting against an object, transferring energy to that object . . .the object might a thermometer. The mass remains the same, but the expanding chamber spreads the molecules out so that there are fewer collisions with each other, and the measuring object or other objects. fewer collisions means lesser energy to transfer, lower temperature." you were very close. But the last sentences were very confusing.
ok, all that is so true, i thought i said it in other ways, but i realize i guess i didn't actually say it clear
22 Sep 07
yeah, i understand that now. there could be fewer collisions and more energy if the molecules were bigger, or more mass, really, like heavier, but since the molecules were the same ones, then it was really that they were slowing down too, since the piston's movement was coming from the energy from the molecules.
gee, i gotta figure out how to say stuff better!
22 Sep 07
Originally posted by adam warlockGood, good. Coquette this is the perspective I was looking for - maybe I was confused by your post.
What you want us to say is that the molecules are transfering their momenta to the piston while colliding with it. And by doing that they're losing kinetic energy.
Now, temperature is just the macroscopic measure of how fast the molecules of the gas are moving. The faster they move the hotter the gas. So, if the molecules are moving with an average low ...[text shortened]... e decreases.
This was a good question btw. The kind of question I like to answer in physics.
22 Sep 07
Originally posted by mtthwWork - perfect -> that is describing the interaction with the molecules to the piston -> transfer of energy OUT of the gas => internal energy of the gas DECREASES => Temperature DROP.
Another way of putting the same point is to say that the gas molecules do work as they collide with the piston. (Work = force x distance)
Ok, good, looks like that mighta been challenging?
Next one to follow...