| Topic: |
Science > Physics |
| User: |
"Lexie" |
| Date: |
24 Feb 2005 11:01:40 AM |
| Object: |
Fluid Statics |
Hi
I recently conducted an experiment whereby you drop pieces of wood into
a large tube of water and recorded, very approximately by eye, the
largest depth the wood reached before it began to raise to the top
again. The woods were about 6mm diameter and various lengths from 5cm
to 25cm and dropped from various heights.
I'm interested in coming up with a model that, quite simply, calculates
where the wood should have reached.
I have tried to take into consideration the forces of buoyancy and drag
but have been told that i cannot create a model without knowing the
time involved (which i don't have). Is this true?
Can anyone help?
Lexie
.
|
|
| User: "Franz Heymann" |
|
| Title: Re: Fluid Statics |
24 Feb 2005 11:44:10 PM |
|
|
"Lexie" <fruit.loops1812@gmail.com> wrote in message
news:1109264500.728833.67810@f14g2000cwb.googlegroups.com...
Hi
I recently conducted an experiment whereby you drop pieces of wood
into
a large tube of water and recorded, very approximately by eye, the
largest depth the wood reached before it began to raise to the top
again. The woods were about 6mm diameter and various lengths from
5cm
to 25cm and dropped from various heights.
I'm interested in coming up with a model that, quite simply,
calculates
where the wood should have reached.
I have tried to take into consideration the forces of buoyancy and
drag
but have been told that i cannot create a model without knowing the
time involved (which i don't have). Is this true?
Can anyone help?
You need to write down the full equation of motion of the wood ,
including the fact that the bouyancy force is dependent on the
instantaneous depth of insertion.
--
Franz
"The great tragedy of science -- the slaying of a beautiful hypothesis
by an ugly fact."
T.H. Huxley
Lexie
.
|
|
|
|
| User: "Uncle Al" |
|
| Title: Re: Fluid Statics |
24 Feb 2005 11:35:26 AM |
|
|
Lexie wrote:
Hi
I recently conducted an experiment whereby you drop pieces of wood into
a large tube of water and recorded, very approximately by eye, the
largest depth the wood reached before it began to raise to the top
again. The woods were about 6mm diameter and various lengths from 5cm
to 25cm and dropped from various heights.
I'm interested in coming up with a model that, quite simply, calculates
where the wood should have reached.
I have tried to take into consideration the forces of buoyancy and drag
but have been told that i cannot create a model without knowing the
time involved (which i don't have). Is this true?
Can anyone help?
How's this: At high velocity impact the wood displaces its own mass
of water. At low velocity impact the energy for water displaced is
equal to the kinetic energy of the wood.
--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf
.
|
|
|
| User: "Franz Heymann" |
|
| Title: Re: Fluid Statics |
24 Feb 2005 11:56:41 PM |
|
|
"Uncle Al" <UncleAl0@hate.spam.net> wrote in message
news:421E105E.3AE0EFBB@hate.spam.net...
Lexie wrote:
Hi
I recently conducted an experiment whereby you drop pieces of wood
into
a large tube of water and recorded, very approximately by eye, the
largest depth the wood reached before it began to raise to the top
again. The woods were about 6mm diameter and various lengths from
5cm
to 25cm and dropped from various heights.
I'm interested in coming up with a model that, quite simply,
calculates
where the wood should have reached.
I have tried to take into consideration the forces of buoyancy and
drag
but have been told that i cannot create a model without knowing
the
time involved (which i don't have). Is this true?
Can anyone help?
How's this: At high velocity impact the wood displaces its own mass
of water. At low velocity impact the energy for water displaced is
equal to the kinetic energy of the wood.
Totally useless and irrelevant or solving the problem
--
Franz
"The great tragedy of science -- the slaying of a beautiful hypothesis
by an ugly fact."
T.H. Huxley
.
|
|
|
|
| User: "Lexie" |
|
| Title: Re: Fluid Statics |
24 Feb 2005 12:14:18 PM |
|
|
What constitues a high velocity? And how does that help?
(They're going in at 1 to 2.6m/s.)
I attempted using suvat equations, however the problem is that the
acceleration, once in the water, is not constant; it increases,
decreases, then becomes 0 (max depth). I tried using dv/dt as the rate
of change of acceleration but again i dont have any measurements times.
Is there any way i can incorporate anything into the suvat equations?
Or any other way i can create a model?
Lexie
.
|
|
|
| User: "Franz Heymann" |
|
| Title: Re: Fluid Statics |
24 Feb 2005 11:58:45 PM |
|
|
"Lexie" <fruit.loops1812@gmail.com> wrote in message
news:1109268858.852514.105200@o13g2000cwo.googlegroups.com...
What constitues a high velocity? And how does that help?
(They're going in at 1 to 2.6m/s.)
I attempted using suvat equations, however the problem is that the
acceleration, once in the water, is not constant; it increases,
decreases, then becomes 0 (max depth). I tried using dv/dt as the
rate
of change of acceleration but again i dont have any measurements
times.
Is there any way i can incorporate anything into the suvat
equations?
Or any other way i can create a model?
You cannot solve it without writing down the complete differential
equation for the vertical motion of the wood, and then set about
solving it.
--
Franz
"The great tragedy of science -- the slaying of a beautiful hypothesis
by an ugly fact."
T.H. Huxley
.
|
|
|
|
| User: "Uncle Al" |
|
| Title: Re: Fluid Statics |
24 Feb 2005 02:04:39 PM |
|
|
Lexie wrote:
What constitues a high velocity? And how does that help?
(They're going in at 1 to 2.6m/s.)
I attempted using suvat equations, however the problem is that the
acceleration, once in the water, is not constant; it increases,
decreases, then becomes 0 (max depth). I tried using dv/dt as the rate
of change of acceleration but again i dont have any measurements times.
Is there any way i can incorporate anything into the suvat equations?
Or any other way i can create a model?
Water is not soft starting around 100 mph.
Do a bunch of runs and fit the curve with a polynomial or a trig
series or whatever. Gnugraph - free - is fully capable of big datset
complex fits. Fast, too.
Uncle Al uses gnugraph to crunch his data,
http://www.mazepath.com/uncleal/
--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf
.
|
|
|
| User: "Franz Heymann" |
|
| Title: Re: Fluid Statics |
25 Feb 2005 12:01:51 AM |
|
|
"Uncle Al" <UncleAl0@hate.spam.net> wrote in message
news:421E3357.A7AE1004@hate.spam.net...
Lexie wrote:
What constitues a high velocity? And how does that help?
(They're going in at 1 to 2.6m/s.)
I attempted using suvat equations, however the problem is that the
acceleration, once in the water, is not constant; it increases,
decreases, then becomes 0 (max depth). I tried using dv/dt as the
rate
of change of acceleration but again i dont have any measurements
times.
Is there any way i can incorporate anything into the suvat
equations?
Or any other way i can create a model?
Water is not soft starting around 100 mph.
Do a bunch of runs and fit the curve with a polynomial or a trig
series or whatever. Gnugraph - free - is fully capable of big
datset
complex fits. Fast, too.
Uncle Al uses gnugraph to crunch his data,
Uncle Al is wasting his and Lexie's time with irrelevancies.
--
Franz
"The great tragedy of science -- the slaying of a beautiful hypothesis
by an ugly fact."
T.H. Huxley
.
|
|
|
| User: "Uncle Al" |
|
| Title: Re: Fluid Statics |
25 Feb 2005 12:45:12 PM |
|
|
Franz Heymann wrote:
"Uncle Al" <UncleAl0@hate.spam.net> wrote in message
news:421E3357.A7AE1004@hate.spam.net...
Lexie wrote:
What constitues a high velocity? And how does that help?
(They're going in at 1 to 2.6m/s.)
I attempted using suvat equations, however the problem is that the
acceleration, once in the water, is not constant; it increases,
decreases, then becomes 0 (max depth). I tried using dv/dt as the
rate
of change of acceleration but again i dont have any measurements
times.
Is there any way i can incorporate anything into the suvat
equations?
Or any other way i can create a model?
Water is not soft starting around 100 mph.
Do a bunch of runs and fit the curve with a polynomial or a trig
series or whatever. Gnugraph - free - is fully capable of big
datset
complex fits. Fast, too.
Uncle Al uses gnugraph to crunch his data,
Uncle Al is wasting his and Lexie's time with irrelevancies.
Depends on whether you want a general theoretical model or a quick
specific heuristic. Organic chemistry is all lies - but they are
really useful lies. Nobody ever passed first year organic doing QM
vs. 1920's LCAO (less the Woodward-Hoffmann rules).
LCAO won't get you very far docking a molecule into a receptor site.
When you go to make the stuff, it's LCAO again - certainly at the
start.
--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf
.
|
|
|
| User: "tj Frazir" |
|
| Title: Re: Fluid Statics |
27 Feb 2005 12:07:25 PM |
|
|
Its bouyancy is 1 pound and its cof of drag is
The hole volume it makes in the water closing .
if its ,,,,,,,,,,,,,,,,,,,, 1 foot where the water closes behind it
the vaccume gap is equal to having more bouyancy ....
The SUM of the above OPOSIT its forward V.
IF 20 pounds is the sum of the V then 20 pounds will stop it .
If the stick lands flat it will displace 20 pounds of water faster.
The one pound stick going in strait will stop
at 20 times its lenth to equal 20 pounds of displacemet to equal the 1
pound stick and 19 pounds of V .
.
|
|
|
|
|
|
| User: "tj Frazir" |
|
| Title: Re: Fluid Statics |
24 Feb 2005 07:35:30 PM |
|
|
Put a sheet of 3/16 plywood on a sheet of styrofoam and tie steets cross
water and ride a dirt bike on the water ,,if you ride fast enouph.
.
|
|
|
|
| User: "tj Frazir" |
|
| Title: Re: Fluid Statics |
24 Feb 2005 07:32:12 PM |
|
|
Water is not soft around 8 knots.
10.2 mph.
below that speed the kenetic weight of impact will equal the water
displaced.
Then higher speeds depend on the hydronamics ..a flat surface would
suck.
An aero would be the best .
It depends how much surface aria and the compresion time of the water.
the compresion time in a liquid that dont compress is the time it takes
to move a volume of mass .
If you yank on the string it will snap .
A small weight will bust the string of you yank quick. Moving the
water is the same thing.
resistance to move .
.
|
|
|
|
|
|
| User: "Lexie" |
|
| Title: Re: Fluid Statics |
24 Feb 2005 12:31:48 PM |
|
|
What constitues a high velocity? And how does that help?
(They're going in at 1 to 2.6m/s.)
I attempted using suvat equations, however the problem is that the
acceleration, once in the water, is not constant; it increases,
decreases, then becomes 0 (max depth). I tried using dv/dt as the rate
of change of acceleration but again i dont have any measurements times.
Is there any way i can incorporate anything into the suvat equations?
Or any other way i can create a model?
Lexie
.
|
|
|
|
|
| User: "Maarten van Reeuwijk" |
|
| Title: Re: Fluid Statics |
25 Feb 2005 04:26:45 AM |
|
|
Lexie wrote:
You need the entry velocity v0 of the stick into the water. Assuming that
the entry effects are not important and that the sticks are completely
submerged immediately, the net buoyancy-force (archimedes) is Fb = Delta
rho * V * g, with Delta rho=rho_water-rho_wood the density difference
between wood and water, and V the volume of the stick. In absence of drag,
and having a constant force the equation for work and kinetic energy reads:
F * x = 0.5 * m * v^2 <=>
Delta rho * V * g * x = 0.5 * m * v0^2 = 0.5 * rho_wood * V * v0^2 <=>
x = 0.5 * rho_wood / Delta_rho * v0^2 / g
here x is the depth that the wood will go.
HTH, Maarten
--
===================================================================
Maarten van Reeuwijk Thermal and Fluids Sciences
Phd student dept. of Multiscale Physics
www.ws.tn.tudelft.nl Delft University of Technology
.
|
|
|
|
| User: "tadchem" |
|
| Title: Re: Fluid Statics |
24 Feb 2005 12:08:53 PM |
|
|
Plot your data.
Do a regression.
Tom Davidson
Richmond, VA
.
|
|
|
|
|
Related Articles |
|
|
