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Subject: Re: [lojban] Direction of Rotation
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On Fri, Aug 10, 2012 at 10:45 AM, Escape Landsome <escaaape@gmail.com>wrote:

> Just to be more precise, I don't really catch what you term a "reference
> frame".
>

A reference frame is a specific point of observation at which the events
take place as described.

Regarding rotational motion, the reference frame is the 3D cubic space
minimally containing the object. The axis of rotation, if extended past the
boundary of the cube, will intersect with two faces. We will call those the
"top" and "bottom" faces.

For most objects, the identity of the "top" face is obvious, as it
corresponds to the top of the object itself. For others, such as Earth, one
must be chosen (North).

If you were to orient yourself in such a way as to be looking at the object
through the "top" face, you would then be in the reference frame to see the
object rotating clockwise.

All that is needed to establish a reference frame when describing
rotational motion is the identity of the "top" of the object.

(Also note that if one person identifies one end of the axis as "top", and
another identifies the opposite end as "top", when one describes the motion
as clockwise, the other will describe it as counter-clockwise, and vice
versa.)

As an example, take a top, turn it upside down, and spin it by turning your
hand clockwise. Since the top is upside down, you label the pointy end as
"top", and say the top is spinning clockwise. Your friend, however, labels
the stick end as "top" because the top of something doesn't change due to
external orientation, and says the top is spinning counter clockwise.
Neither of you are wrong, because you're using two different reference
frames.

-- 
mu'o mi'e .aionys.

.i.e'ucai ko cmima lo pilno be denpa bu .i doi.luk. mi patfu do zo'o
(Come to the Dot Side! Luke, I am your father. :D )

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<div class=3D"gmail_quote">On Fri, Aug 10, 2012 at 10:45 AM, Escape Landsom=
e <span dir=3D"ltr">&lt;<a href=3D"mailto:escaaape@gmail.com" target=3D"_bl=
ank">escaaape@gmail.com</a>&gt;</span> wrote:<br><blockquote class=3D"gmail=
_quote" style=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:=
1ex">
Just to be more precise, I don&#39;t really catch what you term a &quot;ref=
erence frame&quot;.<br>
</blockquote></div><br clear=3D"all">A reference frame is a specific point =
of observation at which the events take place as described.<br><br>Regardin=
g rotational motion, the reference frame is the 3D cubic space minimally co=
ntaining the object. The axis of rotation, if extended past the boundary of=
 the cube, will intersect with two faces. We will call those the &quot;top&=
quot; and &quot;bottom&quot; faces.<br>
<br>For most objects, the identity of the &quot;top&quot; face is obvious, =
as it corresponds to the top of the object itself. For others, such as Eart=
h, one must be chosen (North).<br><br>If you were to orient yourself in suc=
h a way as to be looking at the object through the &quot;top&quot; face, yo=
u would then be in the reference frame to see the object rotating clockwise=
.<br>
<br>All that is needed to establish a reference frame when describing rotat=
ional motion is the identity of the &quot;top&quot; of the object.<br><br>(=
Also note that if one person identifies one end of the axis as &quot;top&qu=
ot;, and another identifies the opposite end as &quot;top&quot;, when one d=
escribes the motion as clockwise, the other will describe it as counter-clo=
ckwise, and vice versa.)<br>
<br>As an example, take a top, turn it upside down, and spin it by turning =
your hand clockwise. Since the top is upside down, you label the pointy end=
 as &quot;top&quot;, and say the top is spinning clockwise. Your friend, ho=
wever, labels the stick end as &quot;top&quot; because the top of something=
 doesn&#39;t change due to external orientation, and says the top is spinni=
ng counter clockwise. Neither of you are wrong, because you&#39;re using tw=
o different reference frames.<br>
<br>-- <br>mu&#39;o mi&#39;e .aionys.<br><br>.i.e&#39;ucai ko cmima lo piln=
o be denpa bu .i doi.luk. mi patfu do zo&#39;o<br>(Come to the Dot Side! Lu=
ke, I am your father. :D )<br><br>

<p></p>

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?hl=3Den.<br />



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