Day 98: Empirical Energy Experiment

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I’ve been doing a lot of thinking about the start of the Modeling Instruction Energy unit. We even talked about it for a significant part of one of our Physics teacher PLC meetings. I started Energy in regular physics about a week ago in regular physics, which started with a demo and then quickly moved on to energy pie charts. Energy pie chart whiteboarding was really fun, but I’m hoping to start my college level class off more empirically.

We did the same demo on day one, but then day two (today) we looked at the area under the Force vs. position graph as it relates to a cart being pulled up a ramp. A force detector is attached to the cart, and a string attached to the detector, and a motion detector is on the ramp pointing up. Today I asked students to pull the cart from point A to B (arbitrary), starting from rest, while graphing F vs. x, then to find the area. I had them do multiple different trials while qualitatively recording what they did while getting from A to B in different ways (speeding up, fast then slow, etc). I found out quickly that I had to have them write down whether they were moving or not when they got to point B, and in the second class I made them do trials first while not moving at B. Anyway, it didn’t take too long for them to notice that the area seemed to be the same no matter what they did if the ended at rest at B. They also noticed that the area seemed bigger if they were moving faster at B. All of this was qualitative.

We then moved on to try to establish a predictive variable for the area. Distance up the ramp didn’t work (hehe) as the same distance on different ramps doesn’t give the same area. Angle has a similar problem; the same angle with different pulling distances gives different areas. Eventually someone mentions height. So then we checked if using the same height with two different angled ramps still gives the same area, and low and behold, it does.

Tomorrow we will investigate the relationship between area and the change in height. I’ll be writing more about the differences between my two classes’ start of the Energy unit at my other blog soonish, I hope.

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