Day 4: Specific Heat and Robots

I really wish I could some how store the energy, enthusiasm and excitement that is just so palpable in both me and my students and the beginning of the year. I’m pretty sure a couple of teaspoons would be all I need to make power my way through February.

In Intro Physics, we are making progress with the battery and peanut question. We made a bit of a side venture to identify various units of energy, and perhaps more importantly, talk about what units aren’t energy. I was trying to stay away from giving definitions to the kids, so when the idea than a volt might be a unit of energy came up, I pointed out that AA, AAA, C and Db batteries all have the same voltage, and my students were able to conclude quite quickly that a volt couldn’t be a unit of energy, since they thought a D cell battery must have more energy than a AA.

After some more calorimetry experiments we returned to the classroom to try to calculate just how much energy it took to raise the the temperature of the water by the amount they measured. At this point, students wanted to know a formula, but we started with the definition of a calorie, which a number of students already knew

1 calorie of energy will increase the temperature of 1 g of water by 1°C

From there, I asked what would 5 calories do to 1 gram of water, and students quickly saw that it would raise the temperature of the water by 5°C. And then we started to think about other things 5 calories might do to a different amount of water. One student suggested it would raise 5 g by 1°C, and then someone realized it would raise 10g by 1/2°C, and we continued to put up different ideas, and one then suggested that it would raise 2 grams of water by 10°C, and this led to an argument, as some could see that this combination didn’t follow the pattern, and others saw that it didn’t make sense for 5 calories to raise the temperature of more than 1 gram of water by more than 5°C. Soon enough, we started talking about dividing that energy equally into 1 gram boxes, and then a student proposed a pattern that the mass multiplied by the temperature change must equal the energy, which led to a great discussion of units, and that while the numbers might work in that equation, the units did not, bringing us back around to the specific heat of water, 1 cal/(g°C), that when multiplied by the mass and the temperature change gives you energy.

Screen Shot 2014 09 05 at 9 26 23 PM

Overall, I think this was one of those lessons where I felt like I was getting more understanding as we were talking, and students were picking up an insight here or there, but I wish I’d had more time to have them do some of this pattern discovery on their own, rather than have me lead them through it.

One other tidbit that I need to make a habit—stopping class with 4-5 minutes to go at the end and simply asking “What did we learn?” and “How did we learn it?” Today, I had to set an alarm on my phone to remind me to have this conversation, and I was so glad that we did—students could clearly acknowledge that they had figured out how to calculate the energy required to increase the temperature of the water, and they had done this through discussion, and without the need for a formula.

In honors physics, we had a great moment where we challenged the students to take the robots that we’ve been using to study constant velocity, and program them such that they all arrived at a position of 2 meters from the origin after 20 seconds, while each robot also had to have a different set velocity while moving. I’m going to try to write up in much more detail how incredible the change to robots from crazy expensive PASCO carts has been for our kinematics work thus far, but for now, I’ll let this video speak for itself.

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About John Burk

The ramblings of a physics teacher.
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