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Re: [Phys-l] representing position and orientation



Mirrors are not well understood by most people, even my best students. You
really have to do labs and ray tracing to figure out how/where images form
in plane mirrors.

I show a photocopy of my palm each year and ask the kids which hand it is.
I never get a consensus. Same thing with adults!

I have them look at the vertex of two perpendicular mirrors for a double
image reversal. This is how others see you. They really like this!
Educational Innovations sells such a mirror, and it is very expensive.


Forum for Physics Educators <phys-l@carnot.physics.buffalo.edu> writes:
Those of us who are old enough can remember textbooks that referred to
images in a plane mirror as being "erect but perverted". Fortunately,
that choice of words has fallen out of favor - and Feynman's insight
simply makes it a mute point. We still have to struggle with how to say
"Uranus" though.

Bob at PC

-----Original Message-----
From: phys-l-bounces@carnot.physics.buffalo.edu [mailto:phys-l-
bounces@carnot.physics.buffalo.edu] On Behalf Of Daniel L Macisaac
Sent: Wednesday, February 15, 2012 10:12 AM
To: Forum for Physics Educators
Subject: Re: [Phys-l] representing position and orientation

This very nice problem is discussed in a Feynman video at
http://www.youtube.com/watch?v=msN87y-iEx0
and the discussion may surprise. Dan M


On Feb 15, 2012, at 10:07 AM, chuck britton wrote:

Different representations for different situations.

This reminds me another 'representational' answer to another 'Silly
Question' that occasionally comes up in an intro Physics environment.

'Why does a mirror reverse left and right but not up and down.'

I've heard 'serious' answers that 'explain' it in terms of our having
two eyes - side-by-side - and our 'brain' figures it out and other
such foolishness.

An easy demonstration of what's going on is (as JD sez) use the
representation that works with a given situation.

If you look into a horizontal mirror (either on the floor or on the
ceiling) it is clear that only up and down are switched. North, South,
East and West are unaffected.

Same goes for a vertical mirror. If it's in the N-S plane then it's
only the East-West directions that are switched. Up and Down stay the
same as do North and South.

Use the representation that works in a given situation.
.
At 4:07 PM -0700 2/14/12, John Denker wrote:
It is difficult or impossible to
express things in terms of northward, southward, eastward, westward,
or other heading-related notions ... but we don't need to do that.
There are other (better) representations we can use.
_______________________________________________
Forum for Physics Educators
Phys-l@carnot.physics.buffalo.edu
https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l

_______________________________________________
Forum for Physics Educators
Phys-l@carnot.physics.buffalo.edu
https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l
_______________________________________________
Forum for Physics Educators
Phys-l@carnot.physics.buffalo.edu
https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l