Granular Materials: Why can you move
through rice but not nails?
Our lab is looking at large aspect ratio (large length to diameter
ratio) granular materials. These materials' resistance to
disturbances is striking. One can easily run fingers through a bucket
of sand, but not through nails. When the aspect ratio is large, a
solid "plug" forms that holds its shape even when the initial
container is removed. This is seen in the pile below, which was
formed by putting acrylic rods (3" long, 1/16" in diameter) in a big
cylinder and then lifting the entire pile by a small (1/4") ball at the
bottom. When the cylinder is removed, the pile retains its cylindrical
shape, supported only by the ball at the bottom.
This plug forms despite the presence of large voids into which
particles could move. The rigidity results from particle
entanglement, which greatly constrains the ability of particles to
Physics Education Research: Student Writing in
Writing assignments are used as a pedagogical tool in nearly every
discipline, including physics. Often these assignments are used
merely to assess student understanding. The thought processes used to
generate a written document, however, may also be instrumental in
helping students internalize and master more difficult topics. Thus
students, when writing, not only display their knowledge, but may also
learn. Our lab is investigating the mechanism by which this learning
occurs --- learning which currently is widely assumed but unexplained.
Explorations in Physics
Based upon physics education research, Explorations in Physics
(EiP) incorporates guided-inquiry techniques with small group
projects in a collaborative learning environment. EiP centers
on common themes that run through the different sciences with an
emphasis on physical science. EiP seeks to instill in students
a level of scientific literacy. A distinguishing feature of
EiP is the emphasis on student-directed projects, on which
students spend one-third of the quarter. Student groups choose a
topic, write a joint project proposal, and work together to design and
conduct relevant experiments. Projects culminate with a written
report as well as a poster presentation. The remaining two-thirds of
the course is spent working through two activity guides which guide
the students through experiments on different topics.
EiP is published by John Wiley & Sons. Visit the
EiP web page for more information.