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*From*: "Richard W. Tarara" <rtarara@saintmarys.edu>*Date*: Fri, 26 Apr 1996 09:36:49 -0500

Just one added point to the other responses. The fact that this problem

is often called the BARN PARADOX is because IF the runner sees the pole

fit in the barn (or between the markers) she will know that it is she

moving and not the barn--a violation of one of the postulates of special

relativity. The whole exercise is to show that she DOES NOT see the pole

fit, and in fact sees just what she should to interpret the sequence as

though the barn was moving towards her. I've worked this out once in gory

detail--involves both time dilations and length contractions.

----------

From: ken_fox@shhs1.ccsd.k12.co.us (ken fox)and I

To: phys-l@atlantis.cc.uwf.edu

Subject: Special Relativity Question / Barn Paradox

Date: Thursday, April 25, 1996 4:32 PM

I need your help again. Here is a paraphrase of a problem from the 1993

IB(higher level exam) that I am struggling with.

A super fast runner has a 4m pole ( her frame) and is moving at 0.866c

relative to me. I have set out two poles in my frame that are 2m apart

notice that her pole fits neatly between the two as she passes. Now,she

sees the two markers to be 1m apart.open

"Does she say that the pole will fit between the markers? Is there a

contradiction here? Explain."

I have run the RelLab simulation of the Barn where the doors close and

so that in my frame they are closed simultaneously ( a key concept hereI

think) when she is in the barn. In her frame the doors do not close atthe

same time but the front and back doors close and shut to allow the polethe

through. Does the runner say the pole fits? The runner sees the front of

pole at the front door long before she sees the back of the pole at theback

door.the

We had a great debate in class and most of us decided she ,too, thought

pole did fit but we are not all (including me) convinced. Can anyonehelp me

out?

thanks

ken fox

--

*****************************************************

Richard W. Tarara

Department of Chemistry & Physics

Saint Mary's College

Notre Dame, IN 46556

219-284-4664

rtarara@saintmarys.edu

FREE PHYSICS INSTRUCTIONAL SOFTWARE AVAILABLE AT

http://estel.uindy.edu/aapt/rickt/software

http://www-hpcc.astro.washington.edu/mirrors/tarara/

---updates are posted often---

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