TTO Demonstration

Kenneth Schug Illinois Institute of Technology
Chicago IL 60616
312-367-3438 (fax3494)


To present phenomenological activities on several science topics.

Strategy & Materials Needed: SEWER LICE A jar is displayed containing dark brown "sewer lice" [raisins]
bobbing up and down in a clear liquid [e.g. Seven Up]. Gas bubbles can be seen
forming on the raisins on the bottom of the container (carbon dioxide gas
dissolved in the beverage); this decreases the density sufficiently to cause the
raisin to rise to the top (like a helium balloon rising in atmosphere). At the
top the bubbles burst, releasing the gas which decreases the density causing the
raisin to sink.

BLOWING WINDS Each group (or individual) is given an empty thread spool, a
small square of paper, a pin and a small piece of transparent tape and given the
following instructions: "push the pin through the middle of the paper and hold
in place by putting the tape over the head of the pin. Now put the pin into one
end of the spool so that the paper lies flat against the spool. Then try to
remove the paper by blowing through the other end of the spool." Performers will
find that the paper sticks to the spool, even when the spool is aimed down,
until they stop blowing. Explanation. A fluid (gas or liquid) in motion creates
a decrease in pressure perpendicular to the direction of flow: in the spool
activity the air passing between the paper and spool end reduces the pressure on
the "inside" surface so that atmospheric pressure on the outside of the paper
holds it in place. This effect is called Bernoulli's Principle and can be used
to explain airplane flight, how atomizers work, etc.

BALANCE POINT Attention is directed to a plastic bird [with outstretched wings]
on the front table which is balancing on its beak [can be passed around the room
from finger to finger]. Next some methods of finding the balance point [=center
of mass or center of gravity] of an object are demonstrated: E.g., support a
meter stick on two index fingers and move them together - they will meet at the
balance point! For irregular flat objects support on thumb and first two fingers
and bring them together [or suspend from two different points near the edge and
draw vertical lines; they will intersect at the balance point.]

DISAPPEARING WATER Presenter claims to be thirsty, picks up an "empty" cup,
pours in water from a container on the table, then walks over to a member of the
audience and inverts the cup over her/his head - no water comes out!!
Explanation: The cup contained a small amount of the water-absorbing polymer
[sodium polyacrylate] used in most disposable diapers. By a process similar to
osmosis, this polymer is able to absorb about 600 times its own volume of (pure)
water; somewhat less tap water.

Performance Assessment:

(Lab Station) Each person (team) is given a 9 x 12 envelope containing a flat
object, access to the following accessories: paper punch, string, tape, pencil,
and instructions to find the balance point by two or more different experimental
methods. They were also asked to suggest a "non-experimental way" to find the
balance point.

Conclusions & References None.

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