Brian NEEDS to know why

Yesterday was a very exciting day during the morning in UE1. Throughout the class so far teachers have continually made comments about just wanting answers and feeling frustrated by these activities which leave all their questions hanging. Yesterday Brian officially declared his need for an answer stating "I NEED to know ... why heat moves from hot to cold." After doing the ET about putting an ice pack in water the class established that energy from the surrounding water moves into the ice until their is an equal distribution of thermal energy in the water and the ice pack. But why should the heat move to the cold to warm it up rather than the cold move to the hot to cool it down? This was what Brian NEEDED to know.

Here is the clip of Brian's question and the class's response.



Brian's question, directly mostly at Eleanor but also to the entire class, then sparked a discussion that lasted for the next half hour (approximately from 23:20 to 57:10 on movie UE1 110629 1144 T4.mp4). The entire class (or at least several active participants) actively worked through different ideas to come to an end conclusion. I thought this process as a whole was really cool because they had been saying the whole time that they wanted answers and here they got an answer, but they got it for themselves by working through the tough ideas together.

The first section of the discussion was somewhat of a random collection of different ideas being thrown out on the table trying to figure out how to approach Brian's question. Joan throws out her intuitive idea, claiming that when she as a person is too hot she just wants to spread out to cool down. Adria then mentions that she's heard the idea that molecules want to spread out to lower concentrations. And Heather brings up a ballistics example where a bullet is shot into gel and transfers all its kinetic energy into heat, waves in the gel, etc. However, Brian is not satisfied by any of these ideas and reiterates WHY hot to cold? At this point Eleanor brings in paper clips to do an experiment with the class that will (supposedly) show that energy moves from hot to cold. She has the class wiggle the paper clips and then put them on the lips to feel the heat. Then wait a few seconds and feel them again to see they've cooled back down. Eleanor explains that they put energy into the paper clip by wiggling it, then that motion energy of the wiggle turned into thermal energy they could feel. Then that thermal energy must have dissipated into the air because the paper clip was no longer warm. This showed that the energy they put IN went OUT to the cooler air. But Brian asked couldn't you also say the coldness of the air went into the paper clip?

And THIS is where it became clear what the issue was. Dorothy helped the class to see that it was equivalent to think of the coldness of the room going into the paper clip and to think of the heat from the paper clip going into the room. It all depends on your point of reference. Scientists have developed the convention that absolute zero exists and anything above that is heat. However, this convention directly contradicts our natural experience (which informs our intuition) because we have a natural point of reference at 98.6 degrees; anything above that feels "hot" and anything below feels "cold." The issue of cold to hot disappears when using the convention because cold doesn't exist in the same way, just less hot. Looking at it from that point of view there is only less hot and more hot. At this point Brian understand where his idea of "coldness" comes from and it finally satisfied with the explanation.


I think this whole progression is extremely interesting because it shows the struggle of the entire class the reconcile their intuition with a scientific convention. Most of the discussion was necessary just to reveal that the issue was a discrepancy in the reference frames being used. The entire time Eleanor and Lezlie were trying to explain the idea of hot to cold using the established convention of absolute zero, while the class was thinking of their natural reference frame at 98.6. Once this difference was realized then it became possible to expose it. Once the class understood the idea that you could pick any reference frame because one was just as valid as any other they became comfortable with the idea of arbitrarily choosing one and sticking with it to be able to communicate consistently about heat motion.