Intriguingly, Sid and later Allie see a causal connection that it is the increasing hitting and collisions of particles that contribute to the increasing temperature/thermal energy, not the increased average speed.
We have found similar lines of reasoning in a study where preservice teachers were asked to generate their own analogies for adiabatic expansion/compression of an ideal gas (which is what the teachers also simulate here) (http://link.springer.com/article/10.1007/s11191-013-9630-5). Also Risto Leinonen describes the line of reasoning: (http://iopscience.iop.org/0143-0807/30/3/016).
We speculate that this idea that "collisions are required to keep the heat up" comes from our own personal experiences of keeping the warmth or even psychologically that we relax after we have stopped arguing with somebody and "cool down."
In the video, there is also an interlude where Stamatis points out that we tend to say heat when we refer to temperature. Tamer Amin has written a paper on how we use the words "heat" (as a verb and noun) and "temperature" in everyday language, using a cognitive linguistics framework ( http://tameramin.webs.com/Amin_csdl-4_paper.pdf), arguing that they are used in different ways structured in a "minimal cognitive model".
I have a learner question here:
ReplyDeleteDebra's question to start the clip is "How is kinetic energy transformed into thermal energy?" I have the same question. I do know that temperature is not the same as heat; my understanding is that temperature is simply the measurement of how fast the molecules are moving. That still leaves the question to me of why faster moving molecules result in something being "warmer" to us, if not because of collisions. Or am I missing something?
KD, I'm interpreting your question to be: "I get that increased KE of particles means increased temperature, but why is that?" I have two answers, but neither satisfies me. The first one is that this is true, by definition. (Blah. Not really an answer.) The second is that I know that hotter things transfer energy to colder things, and that has to do with entropy and energy. (I wrote this out once. If you want me to send you my solution, I'm happy to.) But I bet there's some kind of intuitive answer that connects faster-moving particles to the sensation of higher temperature. Anyone know it?
DeleteAttempt to intuitive answer: Count Rumford's reasoning that boring a hole seems to generate an infinite amount of heat, which led to the idea that heat or thermal energy in essence is motion of particles, might be helpful.
DeleteSimilarly, rubbing your hands converts (bulk) kinetic energy to microscopic kinetic/thermal energy through friction and heating, and therefore leads to higher temperature.
In this example of compressing an ideal monoatomic gas (for instance, helium gas), I would say that the kinetic energy of the gas is identical to the thermal energy. When the wall compresses the gas, bulk kinetic energy is transformed into random kinetic energy through the mechanism of work being performed on the gas.
ReplyDeleteMicroscopically, imagine as a particle being hit by a wall that approaches you. Regardless of your initial speed, your speed is likely to increase in the moment you are hit by the wall. Therefore, as the wall moves, the average speed and average kinetic energy of the particles increase. This is the cause of the increased thermal energy and temperature (which as you say in this context is a measure of how fast the molecules are moving).
Another effect is that the particles get more crammed and therefore collide more with the walls and each other. This leads to an increase in the pressure (force per area unit), but not in itself to increased average kinetic energy of the particles. No energy is added to the system in the collisions once the wall has stopped moving. At fixed volume, energy is only exchanged between the particles during collisions.
Does that help or just confuse?
Jesper - This is a great clip showing Sid's ideas about the PhET sim. I agree that Sid is trying to tell a causal story, but when I listen to Allie, I am not as convinced that she has bought that idea. I hear her say first that both an increase in temperature and collisions is occurring. Then, she questions whether or not one is causing the other (I don't necessarily interpret her as agreeing with that idea). What do you think?
ReplyDeleteAt about 2.25, Allie says "So that an increase in collisions increase our thermal energy?", with a bit of an asking tone in the end, but without really challenging it, I would say.
ReplyDeleteRight, I don't buy that she "sees" it as true or that she buys it. I would say she is questioning it and is unsure based on her tone.
DeleteIn E1 something similar happened. They were writing down (in a whole class discussion) the different types of energy, and then they turned into a very engaged discussion on whether kinetic and thermal energy were the same or not.
ReplyDeleteI was thinking on going back to that, but now I am definitely going to look for those episodes tomorrow! I think having different perspective in the same concerns can be very rich for analysis.
I really like what Stamatis said about words. I am very interested in using professional terminology by students vs. their understanding of what these word actually mean. Great clip!
ReplyDeletePhysics talk: I feel like there's a chicken and egg phenomenon going on here. The two sides of the story I see are these: Is it the increase in avg speed of particles that leads to more collisions (and higher temperature)? Or is it more collisions leads to higher average speed (and higher temperature)?
ReplyDeleteMy thought: Are they linked so tightly that we can remove the idea of causality and consider these two ideas as simultaneous occurrences? If container of particles is exposed to an extreme temperature, the particles in the box will "heat up" and move faster, therefore colliding with the walls more often. But if instead, the volume of the container is reduced, more collisions will occur, increasing the average speed of each particle and thereby increasing temperature (assuming a non-adiabatic compression, I think?). So it could be either one.
Clearly there are incorrect ways to talk about this PhET, and confusion with words such as heat. But is there a single correct way to describe these processes in all cases, or does the phrase "it depends..." apply here?
I'd say it's one direction only:
DeleteMore speed/kinetic energy leads to more collisions and higher impact collisions.
The other way around: When two particles collide, energy is exchanged, but the average kinetic energy (and speed) does not increase.