## PSN-L Email List Message

Subject: Re: Pendulum Q
From: ChrisAtUpw@.......
Date: Wed, 24 Jan 2007 20:33:55 EST

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In a message dated 24/01/2007, Brett3mr@............. writes:

Let me  borrow Einstein's thought-experiment box, the one with
no windows that is  big enough to let me get inside. Sitting in the box, I
coat the  bottom with thought-experiment ice, the kind that has no
friction. Then I  set a 1Kg brass weight on the ice in the center of the
floor and wait for  the thought-experiment earthquake to occur, which
happens right on  time. Being that the quake is conveniently close, I
observe that the  mass appears to be moving, which I record with my video
camera. The  question is, what am I observing when I plot the motion of the
weight? And then, can I tell anything about the nature of the motion  of
the box (i.e. ground velocity or acceleration) from analyzing the  weight's
apparent motion inside the box? Also, I observe that, since  there can be
no (horizontal) force acting on the weight because of the  ice, it will be
seeing no (horizontal) acceleration at  all.

Hi Brett,

You are recording both the position and the time of  relative movements
of the mass. From this you can infer the lateral acceleration  and velocity of
the frame of reference, if you know that the mass is not  being accelerated.

Regards,

Chris Chapman

In a message dated 24/01/2007, Brett3mr@............. writes:
<=
FONT=20
style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size=
=3D2>Let me=20
borrow Einstein's thought-experiment box, the one with no windows that=
is=20
big enough to let me get inside. Sitting in the box, I coat the=20
bottom with thought-experiment ice, the kind that has no friction. The=
n I=20
set a 1Kg brass weight on the ice in the center of the floor and wait=20=
for=20
the thought-experiment earthquake to occur, which happens right on=20
time. Being that the quake is conveniently close, I observe that=20=
the=20
mass appears to be moving, which I record with my video camera. The=20
question is, what am I observing when I plot the motion of the=20
weight? And then, can I tell anything about the nature of the mot=
ion=20
of the box (i.e. ground velocity or acceleration) from analyzing the=20
weight's apparent motion inside the box? Also, I observe that, si=
nce=20
there can be no (horizontal) force acting on the weight because of the=
=20
ice, it will be seeing no (horizontal) acceleration at=20
all.

Hi Brett,

You are recording both the position and the tim=
e of=20
relative movements of the mass. From this you can infer the lateral accelera=
tion=20
and velocity of the frame of reference, if you know that the mass is no=
t=20
being accelerated.

Regards,

Chris Chapman
```