3B Scientific Air Cushion Plate - Handbuch (Seite 67)

Physical Experiments on the Air-Cushion Table
16
Then reduce the area available for the hover discs
to half its size. To do this, lift up magnetic barrier
no. 2 and reattach it so that it separates the
experiment surface into two halves, with its ends
snapping into the recesses provided in barriers
no. 3 and no. 4. Now set both hover discs into
motion in the same way. Count the number of
impacts one of the hover discs performs with the
magnetic barriers within the same period of time
as in the previous experiment.
Result:
In the first experiment, the number of impacts with
the barriers is lower than in the second. By reducing
the area to half its size, the number of impacts
increases to approximately the double amount.
Interpretation:
Reducing the volume of a vessel containing a gas
causes an increase in the number of impacts of
the gas molecules with the vessel walls within a
specific period of time. Since the number of im-
pacts occurring in a specific period of time with
a specific wall is an indicator of pressure, the
conclusion is that reducing the volume increases
the pressure.
Note:
Evaluation is easier when counting only the
impacts with magnetic barrier no. 2 in each of
the experiments. This, however, requires longer
times of measurement.
It is also possible to ascertain the total amount of
impacts of both discs. In this case it is recom-
mended that one student counts the impacts of
the red disc while another student counts those
of the green. The results are then added up.
2.1.5 Mean Velocity of the Molecules
– Temperature of a Gas
Components:
Air-cushion table with fan
Overhead projector
Magnetic barrier, long
2 Pieces
Magnetic barrier, short 2 Pieces
Hover discs, red 16 Pieces
Model simulation
Real Object Model
Vessel containing Experiment surface of
the gas the air-cushion table
Walls of the vessel Magnetic barriers
Gas molecules Hover discs
How to proceed:
Align the air-cushion table horizontally and attach
the magnetic barriers.
Position all hover discs in one corner of the
experiment surface so that the spaces between
them are approximately 1 cm.
The fan is turned to a medium setting.
Sequentially observe the motions of each of the
hover discs. Draw attention to the velocity of each
disc in relation to the velocity of all other discs.
Gradually turn down the fan so that all hover discs
come to a stop and then turn it up again so that
they are sure to lift off. The same observations
are repeated at a lower velocity.
Result:
The velocity of each hover disc changes with each
impact. While an impact with the vessel wall