Date: Fri, 03 Dec 2004 09:04:20 -0600

Author: Gary Karshner

Subject: Re: buoyancy


If you consider the whole apparatus that undergoes the oscillation
as a system each part of it under goes the same changes in acceleration.
Years ago, you showed me a variation of the cart that shoots up a ball and
catches it, when the velocity is constant. Your variation was to accelerate
the cart first with weight and string over a pulley, and then by inclining
the track. In the first case the outside force accelerates the cart after
the ball is ejected and the ball misses the cart. In the second case both
the ball and the cart (a system) under go the same acceleration and thus
the cart catches the ball. In this case both the container and the float
undergo the same outside acceleration and thus remain fixed relative to
each other.
I hope this help, your inclined track was big help in my
understand the concept of a system.


At 08:32 AM 12/3/2004 -0500, you wrote:
>I guess my hang-up is in switching from an accelerated frame of reference
>to the "lab" frame. In the accelerated frame, the upward acceleration
>(for example) is taken care of by the fact that the buoyancy force has
>increased by the appropriate amount (g+a). I think my confusion lies in
>trying to imagine the mechanism or sequence of events in the lab frame. I
>too imagine that the object would sink lower for an "instant" but that
>really doesn't seem to happen. It's so easy to invoke the equivalence
>principle and simply say that g has changed. But visualizing it otherwise
>is not so easy (for me). --
From Fri Dec 3 10:05:26 2004