The sample experiments shown here illustrate the behavior of fluids,
flames, and mechanical systems in microgravity. After each description,
a picture of the experiment, followed by its appearance in normal
gravity (1g) and then micro-gravity (ug) are given.
The weight (W) of a body of mass (m) in a gravitational field of strength
(g) is given by W=mg. In microgravity, g is virtually eliminated and
therefore the weight of the body is also eliminated. To demonstrate
this principle, a mass on a scale is dropped. The two counterbalancing
forces in this experiment are (1) the gravitational force acting on
the mass and (2) the force of the spring in the scale. During the drop,
g tends towards zero and the restoring spring force pushes the indicator
from the original weight of the body toward zero. Shown in figure 3.
Fig. 3. - Weightlessness (normal
gravity shown in the image on the left and microgravity is shown
in the video on the right).
The fluid interface experiment highlights the role of surface tension
in the absence of gravity. In 1g, the effect of surface tension is evident
only near the container walls and most of the surface looks flat. In
reduced gravity, surface tension leads the liquid to assume a very different
shape. Specifically, the liquid creeps up the walls of the container
by capillary forces; this is most evident in the corners. Given enough
ug time, the liquid would wet the walls of the vessel, leaving a bubble
of air in the center. Shown in figure 4.
Fig. 4. - Fluid Interface (normal
gravity shown in the image on the left and microgravity shown
in the video on the right).
The candle flame experiment demonstrates the effect of buoyant convection
and its absence on combustion phenomena. In normal gravity (1g), the
combustion gases are much hotter, and thus lighter than the surrounding
air. Buoyancy causes the hotter, less dense combustion gases to rise,
giving the candle flame its vertically-elongated, conical shape. However,
during the drop experiment, the hot gas expands in all directions. As
a result, the flame becomes shorter and wider. In longer periods of
reduced gravity, the flame becomes spherical and entirely blue. This
was observed in a candle flame experiment performed on the Space Shuttle
(USML-1/STS-50, June-July, 1992). Shown in figure 5.
Fig. 5. - Candle Flame (normal gravity
is shown in the image on the left and microgravity is shown in
the video on the right).
Two magnets are oriented with like polarities opposing one another (i.e.,
N-N or S-S). The lower magnet is fixed to the experiment platform while
the upper magnet is freely supported on a lever arm. In 1g, the upper
magnet is levitated by the magnetic repulsive force which is balanced
by the gravitational force pulling the upper magnet downward. During
the drop, the magnetic repulsion becomes dominant and the upper magnet
moves rapidly away from the lower magnets. Shown in figure 6.