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*From*: Josh Gates <jgates@tatnall.org>*Date*: Thu, 07 Jan 2010 07:32:39 -0500

Hi everyone,

I haven't dealt with action in a long time, so I'm a bit fuzzy on the particulars at the moment. Here's what I'm trying to do:

Given a starting point (0,0) and an ending point (5m, 9.08m), I'm trying to show that the parabolic path beginning with a 70 degree initial angle from +x (the path given by N's laws, kinematics, etc.) minimizes the action.

Here's how I'm trying to do it (which apparently has one or more flaws):

- I made a spreadsheet, with the columns x, y, v, KE, PE, E, K-U

* x increments in .1 m steps from 0 to 5m

* y is a function of x, defining the path

* v is root(v_i^2-2gy), satisfying cons. of E

* KE and PE are defined in the ordinary way

* E is there to check my formulas, verifying cons. of E

* I average all of the K-U entries to give something similar to the action

Since the x steps are all the same, integrating K-U dx and dividing by the total delta x should give me the same thing that the average does (I think). It occurs to me now that there's a problem with paths that go straight up at any point, but I'm willing to work with that later. My current issue is that there are other parabolic paths that give a lower K-U average than the correct path.

Anyone see where I went awry?

Thanks,

Josh

--

Joshua Gates

Physics Faculty

Tatnall School – Wilmington DE

Johns Hopkins Center for Talented Youth

**Follow-Ups**:**Re: [Phys-l] Action***From:*John Denker <jsd@av8n.com>

**Re: [Phys-l] Action***From:*Ken Caviness <caviness@southern.edu>

**Re: [Phys-l] Action***From:*"Bob Sciamanda" <treborsci@verizon.net>

**Re: [Phys-l] Action***From:*John Mallinckrodt <ajm@csupomona.edu>

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