Re: Fluids Physlet

[Bob Sciamanda <trebor@VELOCITY.NET>]

If r = the fraction of wood above water, then I get:

r = (wood - water)/(oil - water),  where wood, water and oil are the
densities of these things.  This is independent of the oil height.  This
looks like A!
Forgive my condensed notation - I am in a hurry. The calculation was also
hurried (???)  Will re-check later.

Bob Sciamanda (W3NLV)
Physics, Edinboro Univ of PA (em)
trebor@velocity.net
http://www.velocity.net/~trebor
----- Original Message -----
From: "Stuart Leinoff" <Leinoffs@ACC.SUNYACC.EDU>
To: <PHYS-L@lists.nau.edu>
Sent: Monday, August 18, 2003 3:35 PM
Subject: Fluids Physlet


> Greetings,
>
> Ok, I am stumped by the Physlet on fluids found at (among other place=
> s):
>
> http://webphysics.davidson.edu/physletprob/ch8_problems/ch8_11_fluids=
> /fluids_2.html=20
>
> The alleged answer is that "B" is the only "physical" animation, but =
> I do not see why the block of wood will float higher in this animatio=
> n as oil is drawn away but before the block of wood breaks the surfac=
> e of the oil.
>
> By Archimedes Principle and the equilibrium principle, the weight of =
> the block (constant) should equal the weight of the fluids displaced;=
>  which would be the sum of the (oil displaced)'s weight and the (wate=
> r displaced)'s weight.  Why would the ratio of these two weights chan=
> ge when the block is less deep under the oil?
>
> If we calculate the buoyancy force based on the difference between th=
> e water's pressure pushing up on the bottom surface of the block and =
> the oil's pressure pushing down on the top surface, again I do not se=
> e why this "difference" would be different before the oil no longer c=
> overs the top surface of the block.
>
> Animation "A" does not seem physical to me because once the block is =
> no longer under the oil, it should sink deeper into the water.
>
> I would appreciate someone else's insight into this.
>
> Thanks,
>
>
> Stuart Leinoff
> Professor of Physics
> Science Division Chair
> ACC