I'll move quickly through harmonic motion, as always. The new pace will mean spreading out the problem sets so there's generally only one short question per night, and probably doing an extra full-on linearization experiment with springs. My plan for now is to move through the first contact with energy at a bit slower pace than normal - say, three weeks rather than two. Thanks for the question, Matt! I'm sorta in the same place - only difference is I've done momentum but not energy. Any commentary on whether I should finish those units as scheduled and then have extra extra time to study for the test, or should I slow those units down significantly, or should I delay starting them, and for the first 3 weeks or so discuss the previous units? I suppose this is a good problem to have. So as I look at things, all I have left is momentum and collisions, and rotational dynamics. Anyways, before the news, I had gotten through the basics of motion, kinematics, force (including centripetal fore), and energy. I'm the stereotypical "Long time listener, first time caller," guy. I read your material here and other places often, though I rarely post. Matt Freeze writes, in the comments section of the post about how AP Physics 1 will cover mechanics-only from now on: We each tested the questions in the "come and show me" exercise, and they all seemed to work fine!) (If you have operation requests or if you find bugs, please post a comment or email me - I can ask the author for changes. The main benefit of Milo's simulation over the others I've seen online is that it's easy and fast to make quick quantitative changes to the initial speed, radius, and mass values to check whether an orbit is circular. Please explore - just as on the original PHET, it's possible to drag the velocity arrow, to add additional planets, and generally to explore trajectories. It works well for me on either my windows PC or my iPhone in chrome. Milo's Solar System works best with chrome as your browser. (Or most likely, they ask for help from a classmate.) If their solution was incorrect, they find out for themselves! They either redo their prediction, or they come back to ask for help. The student brings me a screenshot of a circular orbit with their new values of mass and/or speed and/or planet position. I check that they've used Newton's law of gravitation and circular motion methods then whatever their answer, I have the student use the simulation to check whether they in fact get a circular orbit with their result. They come to my desk to show me their solution. I use it as a "come and show me" exercise - I give one randomly to each student. I've written out twelve different versions of this question in this file. But, we know that the speed has to be root-2-times bigger than before to keep a circular orbit! So, click on "undo motion", and change the vy value from 100 to 141. Change that to 200,000 and hit play - the yellow planet glides off the screen, obviously not in a circular orbit. You'll see its mass as "100,000" arbitrary units. To solve the "double the central planet's mass" problem I posed above, click on the big blue central planet. Open it and press play - you'll see the yellow planet in a circular orbit. We have one.įor his senior community service project, Milo Jacobs has essentially replicated "my solar system." I'll call it " Milo's Solar System" for now. Now that flash is gone, we need a replacement for the phet simulation. You can see me performing several calculations and experiments as quantitative demonstrations in this College Board video. And the gravitational force is too weak to set up a small-scale solar system in the lab.įor years, I've used the free PHET simulation linked above to show, if not real experimental evidence, at least something that has the look and feel of an experiment. How to do that? I can't very easily double the mass of the Earth, then speed up the moon by 40% to see if it still orbits in a circle. My students expect that the next step after any mathematical solution is to provide experimental evidence. * Also known as the Factor of Change method So by Bertha's Rule of Ones*, doubling the mass means the factor of change for the speed is root(1*2/1) = root 2. Solve for speed v - you get root ( GM/d). I can *predict mathematically* how to retain a circular orbit when the mass of the central planet is doubled: Set the formula for gravitational force equal to the centripetal force. See, I can't do live experimentation with gravitation. Here's a link to the 2021 replacement: Milo's Solar System. I only care about two sites that will no longer be functional after flash is deprecated:, and PHET's " my solar system" orbit simulator (screenshot shown).
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