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This exercise has two parts: a model formulation and
calibration phase and a model validation or test phase. In
the first, students create a model in addition
to that based on Torricelli's Law and
choose the placement and shape and sizes of holes in buckets
to parameterize the models. In the second, an ``Evil Genius''
creates buckets with holes for students to test their models
against.
The following materials are needed:
- 1-quart plastic jugs such as those containing milk or
juice for use as the leaky buckets
- Drill and bits to create circular holes
- Scapels for cutting non-circular holes
- Stop watches
- Graduated cylinders for volume measurements
- Plastic dish washing tubs for water if a large sink is
not available
- Ring stands and plates for elevating the buckets
It is up to the students to ensure that they have plans to
measure all the parameters needed in their models. This may
involve different levels of ingenuity, flexibility, and
special equipment from the instructors, depending on the
models used.
The Evil Genius will play by a few rules to ensure that
unreasonable test buckets are not created. For example, if E.G. wishes to
cut more than one hole, he should cut the holes at the same vertical level.
In particular, similar plastic jugs will be used. Holes on more than one
level will not be used. Otherwise, shape, size, and number of holes will
be freely created.
This exercise can be tuned for more or less difficulty depending on
instructors' aims and students' abilities. For example:
- Use a bucket with a regular, but vertically-varying cross-section.
- Put holes at different levels to illustrate problems with coupled
models.
- Vary the fluid or change the surface tension by adding a drop or two
of dish-washing liquid.
- Alter the local gravity field, or induce a time-varying gravity field.
Our students were easily able to suspend iron filings colloidally in the
fluid and examine the behavior of the leaky bucket in a rapidly-rotating
magnetic field by the end of the lab.
Next: Leaky Bucket - Student
Up: Leaky-Bucket Experiment
Previous: Leaky-Bucket Experiment
James Powell
2000-07-30