[Phys-L] Re: Buoyancy question

[hfakhrud at BSU.EDU (Fakhruddin, Hasan)]

Rick,
Does the chicken land back in water and float?   If not, you can add one more object to the list: a buoy or a beach ball chucked into the pool.

________________________________

From: Forum for Physics Educators on behalf of Rick Tarara
Sent: Wed 12/8/2004 8:52 AM
To: PHYS-L@LISTS.NAU.EDU
Subject: Re: Buoyancy question



As John D said, there are any number of complicating factors here, but to
keep it simple, the overall density of the OBJECT must be less than the
density of water for it to float.  The iron ship must be shaped properly so
that it will retain a large internal volume of air (or other light material)
so that the total mass divided by the TOTAL volume remains less than the
density of water.  [The shape must also prevent water from flowing into the
interior, but a simple 'shoebox' shape is easiest to analyze.] I always pose
this same question to my students, but add:  How can a wooden ship sink and
how can a steel ship float in light of their densities?

A really good example of the principle is an aluminum canoe designed to have
a neutral buoyancy when completely filled with water [which happens every
time I go canoeing].  The secret is in the bow and stern or the canoe.
These wedge shaped volumes are filled with a floatation material that
insures that the overall density of the canoe, even when filled with water,
is just slightly less than that of water.  This helps one recover a canoe
after falling out and being swamped.  ;-)

The other good problem to pose to students is:  You are sitting in a rowboat
that is floating in a swimming pool.  You have a banana, a chicken, and an
iron anchor with you in the boat.  You eat the banana, the chicken flies
away (well they can sort of fly a short distance), and you throw the anchor
into the pool.  In each case, what happens to the water level in the pool?

Rick

*********************************************************
Richard W. Tarara
Professor of Physics
Saint Mary's College
Notre Dame, Indiana
rtarara@saintmarys.edu
********************************************************
Free Physics Educational Software (Win & Mac)
NEW: Animations for PowerPoint
          New Simplified  Energy Management Simulator
www.saintmarys.edu/~rtarara/software.html
Energy 2100--class project
www.saintmarys.edu/~rtarara/ENERGY_PROJECT/ENERGY2100.htm
********************************************************
----- Original Message -----
From: "Fakhruddin, Hasan" <hfakhrud@BSU.EDU>
To: <PHYS-L@LISTS.NAU.EDU>
Sent: Wednesday, December 08, 2004 8:35 AM
Subject: Re: Buoyancy question


> I was refering to the fact that an iron nail sinks in water but a ship
> made of iron floats.
>
> Hasan Fakhruddin
> Instructor of Physics
> The Indiana Academy for Science, Mathematics, and Humanities
> BSU
> Muncie, IN 47306
> E-mail: hfakhrud@bsu.edu