AP Physics: Pushing Blocks
Students worked on a problem I’ve come to really like where three blocks of different masses are being pushed along by a certain force. Based on some of the struggles a few groups were having, I think it would be worthwhile to pause sometime soon to do a model summary. I loved the moment when students figured out how to use the 3rd Law to think about the normal forces between each pair of blocks. The best thing I overheard, though, was a student who said “You need to convince me you’re right! If you can explain your idea and your evidence, then I’ll believe you.”
Earth Science: Kepler’s 2nd Law
Students plotted the position of Mars along its orbit, then cut out some wedges that represent the same amount of time. We used the mass as a stand-in for area to show that an orbiting object sweeps out the same area in the same amount of time. We got really nice results; the class average for the mass was within 0.01 g for the two wedges. I think students lost track of what they were plotting, however, so I need to think about how I can reinforce what the numbers they are plotting has to do with the actual path of Mars.
5 thoughts on “Day 38: Pushing Blocks & Kepler’s 2nd Law”
I really like both of these activities. I haven’t really done that AP problem before but I can see how it’d be really powerful with students. I like how it brings unbalanced forces and Newton’s Third Law pairs in one nice extending think. For the Earth Science activity, it might make more sense if you started with a perfectly circular orbit and ended with something crazy like Halley’s Comet. Mars isn’t a circular orbit but it’s pretty close. I wonder if it’d work out. I like reading your blog. It gives me ideas. Thank you for writing it. #NaBloCoMo
Thansk for the comment! I really like the idea of repeating the Earth Science activity with a comet. When we do comets soon, one of the characteristics we’ll chwck out is the shape of their orbits, which would be a great time to see if Kepler’s Laws still apply. Now to find a scale diagram of a comet’s orbit!
Here’s an HTML app for drawing ellipses, complete with divisions to represent equal time! http://www.uwgb.edu/dutchs/Geometry/HTMLCanvas/Kepler2Law5.htm
That. Is. Amazing. I gotta do this activity!
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