Before you start your lab report, it might be useful to
look at a sample
report.
Lab: Fluid
Flow
Purpose of
experiment:
We want to know what law applies for water draining from
a cylindrical container. We can imagine two different
scenarios:
Flow of an ideal fluid:
Here the rate of change in the height of the liquid in
the container will be proportional to the square
root of the height, and we arrive at the time
dependence of the height:
h(t) = ho - a
· t + b ·
t2
where a and b
are two constants to be determined by the experiment,
and ho is the beginning height. (This
derivation uses Bernoulli's
Law.)
Flow of a viscous fluid:
Here the rate of change in the height of the liquid in
the container will be proportional to the
height, and we arrive at the time dependence of
the height:
It is the purpose of this experiment to find out which
of the two scenarios describes this particular physical
reality better.
Video clip of
experiment: Larger
size, (280 kB, Sorenson compression) or smaller
size (176 kB, cinepak compression) versions are
available. The are recorded in time-lapse, with 3 seconds
between frames. Since they will play at 8 frames per
second, the roughly two minutes that it took to drain
this container are compressed to less than 5
seconds.
Instructions for performing
the experiment:
Run the Java applet by clicking this
button:(It will open in a separate window).
Digitize the height of the liquid column by
clicking on the upper limit of it. After each click,
the mouse position is recorded and the movie is
advanced one frame. You should try to devise a
consistent strategy on where you click (left, right,
center, ...). If you make a mistake, click on the
"Undo Pt." button in the
applet, and the last point will be erased. Please
Note:If you are using a
phone line to perform this experiment, then please
keep in mind that it can take a couple of seconds
between two successive frames of the video you are
digitizing. Please do not get impatient. You can see
when the next frame is ready for you from observing
the text area: as soon as the result of your previous
click is displayed, the next video frame is ready for
processing.
You can display the points that you have already
digitized before by clicking on the "Plot y(x)"
button. It will turn red and show the points overlaid
on the video. Clicking the same button again will turn
this feature off.
You can also plot the trajectory as a function of
time directly within the applet by clicking on the
"Plot h(t)" button. Clicking on the "Digitize" button
will bring you back to the data input mode.
The numerical data you have collected are
displayed in the text area on the right side of the
applet. After you are done digitizing all frames,
please copy your data into your clipboard and export
them into your favorite spreadsheet or graphing
program. There, you can fit the above two functional
dependencies to your data and decide which one fits
better.
Now produce a plot with your graphing program or
by screen-capture of the applet.
Finally, write the report with your favorite word
processor or text editor and email it (as email
attachment) back to the instructor.