Monday, July 23, 2012

NYC Modeling Workshop: Day 11

Today was a bit of a blur: We zoomed through both projectile motion and circular motion. I'm working up my store of questions to ask students when they present whiteboards, along with potential modifications to the standard problems and labs. Watching Mark's patter as he leads us through the labs is really fun. I hope to be half as good as he is within the next five years.

Some standout (but not necessarily new) ideas:

  • Explicitly relate the x-t graph to the motion of the projectile's shadow on the floor (when illuminated from directly overhead) and the y-t graph to the projectile's shadow on the wall (when illuminated directly from the positive/negative x-direction).
  • As an extension, have advanced students make a video of something with significant air resistance being tossed instead of a nice, aerodynamic ball.
  • Tie all 'errors'/'limits to precision' back to 'tools, techniques, and environment'.
  • The spinning-track CFPM demo apparatus is awesome.
  • Use a video of the whirling stoppers lab done badly to discuss safety and reliability issues with students.
  • To help students visualize force diagrams, build 3D versions out of straws and putty.
There was some debate about whether tangential velocity increases when you increase the centripetal force and radius is free to change, or if it just looks faster because the angular velocity increases. Anyone know?

2 comments:

Brian said...

I think the answer depends on whether in the process you do work on the object. If you are doing work, then the speed changes because there is a change in KE. If you aren't doing work in the process, then the speed must remain the same. To do no work, your force must be perfectly perpendicular to the path at every point. The question then is this, "What is the shape of path of an object that spirals inward or outward without changing speed?" or is such a path not possible.

Mr. Burk said...

What is the spinning track CFPM apparatus?