3B Scientific Air Cushion Plate - Handbuch (Seite 68)

17
Physical Experiments on the Air-Cushion Table
causes only a change in direction, a collision of
two hover discs usually causes a change in speed
as well.
At any given point in time, the majority of the hover
discs move at a mean velocity. Only few hover
discs have a high and few a very low velocity.
Model simulation
Real Object Model
Vessel containing Experiment surface of
the gas the air-cushion table
Walls of the vessel Magnetic barriers
Gas molecules Green hover disc
Foreign gas Red hover disc
molecule
How to proceed:
Align the air-cushion table horizontally and attach
the magnetic barriers. Closely arrange the green
hover discs in one corner of the experiment
surface so that the spaces between them are
approximately 1 cm.
Turn up the fan so that all hover discs are sure to
lift off.
Place the red hover disc in the middle of the
experiment surface, holding it with the finger and
then releasing it so that it is not in motion at first.
Observe the motion it subsequently performs.
Then place the red hover disc directly into one
corner of the experiment surface, holding it with
the pointer and then quickly releasing it so that it
moves in the direction of the center at high
velocity.
Result:
In the first experiment, the red hover disc
repeatedly receives impacts from the green discs.
Its motion then no longer differs from that of the
others. In the second experiment, the velocity of
the red hover disc is reduced by collisions with
the green ones, so that its motion then also
corresponds to theirs.
Interpretation:
If a foreign gas molecule penetrates into a gas it
cannot continue in its state of motion. The inter-
action with the other gas molecules adapts its
motion to theirs after a short time.
2.1.7 Velocity of Molecules in a Gas
Compound
Components:
Air-cushion table with fan
Overhead projector
Magnetic barrier, long
2 Pieces
Magnetic barrier, short 2 Pieces
Hover disc, red 12 Pieces
Hover disc, orange 2 Pieces
Interpretation:
The molecules in a gas have different velocities.
The velocity of each gas molecule changes with
each impact. Many molecules move at a velocity
that is close to the mean velocity. Only few mole-
cules have a very low or high velocity. The distri-
bution of velocity is constant over time in a large
number of molecules. The mean kinetic energy of
the molecules characterizes the temperature of the
gas. A low mean kinetic energy corresponds to a
low temperature, a large mean kinetic energy to a
high temperature. In each case there are mole-
cules whose velocity is very low and others which
are especially fast.
Note:
To ensure better visibility of the motions of a
specific hover disc, use 15 red hover discs and 1
green one rather than 16 red ones.
2 1.6 Mean Velocity of the Molecules
– Influence on Foreign Molecules
Components:
Air-cushion table with fan
Overhead projector
Magnetic barrier, long
2 Pieces
Magnetic barrier, short 2 Pieces
Hover disc, green 12 Pieces
Hover disc, red l Piece