Physics of Motion – Andy’s Question

From: Andy Date: October 29, 2009 12:35:37 AM To: Walter Stroup Subject: follow up

Dr. S.,Attached is the physics TAKS question I mentioned. The use of "causes" to me implies that the continual rising is due to some outside force or other phenomenon. Perhaps aliens are beaming her up?

Also, could you send the Newtonia video that you showed me on Wednesday? I can come in with a zip drive to get the larger file another time.

From: Jill Marshall marshall@mail.utexas.eduTo: Walter Stroup <wstroup@mail.utexas.edu>Subject: Re: TAKS ItemDate: Sun, 1 Nov 2009 16:57:11 -0600

This is not from one of the years that TPAT reviewed, so I'm just speaking for myself at first glance, but I agree that it's a bad question. If you can make the argument for mass, you can make the argument for inertia, so that's at least 2 answers. I expect TEA would argue that "reaction force" is a better answer, but it really is not. I would bet that the center of the child does not rise at all while the force from the trampoline is in play; OK maybe the center of mass. (Have to go pay the kids down the street a dollar to jump on theirs and let me video it.) At that point it's the inertia that causes her to rise. Actually I would say that nothing causes her to rise- she is in motion so she stays in motion.

Is this from last year's test?