OBJECTIVE:

To use a plasma sheet to observe acceleration forces that are experienced on board a space vehicle.

BACKGROUND:

The accelerations experienced on board a space vehicle during flight are vector quantities resulting from forces acting on the vehicle and the equipment. These accelerations have many sources, such as residual gravity, orbiter rotation, vibration from equipment, and crew activity. The equivalent acceleration vector at any one spot in the orbiter is a combination of many different sources and is thus a very complex vector quantity changing over time. The magnitude and direction of the vector is highly dependent on the activities occurring at any time. The accelerations also depend on what has happened in the recent past due to the structural response (e.g., flexing and relaxing) of the vehicle to some activities, such as thruster firing, etc.

On the other hand, the gravity experienced on Earth is a relatively stable acceleration vector quantity because of the dominating large acceleration toward Earth's center. Some activities, such as earthquakes and subsurface magma movements and altitude changes, may perturb local gravitational acceleration.

Gravity and artificial accelerations may be investigated and demonstrated visually by using a common toy available in many toy, novelty, and museum stores. The toy consists of a clear, flat, plastic box with two liquids of different densities inside. By changing the orientation of the box, droplets of one liquid will pour through the other to the bottom. For the purposes of this activity, the toy will be referred to as a plasma sheet.

MATERIALS NEEDED: Plasma sheet toy Record turntable File cards Overhead projector Slide projector Projection screen

PROCEDURE: Step 1. Lay the plasma sheet on its flat side on the stage of an overhead projector. Project the action inside the sheet on a screen for the entire class to observe. The colored liquids will settle into a dispersed pattern across the sheet. Step 2. Raise one end of the sheet slightly to add a new component to the acceleration vector, and support it by placing a one-centimeter-thick pile of file cards under the raised end. Observe the movement of the fluids inside. Step 3. Raise the end of the plasma sheet further and support it with another stack of cards. Again, observe the movements of the fluids. Step 4. Aim the slide projector at the screen. Project a white beam of light at the screen. Stand the plasma sheet on its end in front of the projected beam to cast shadows. Observe the action of the falling liquids. Step 5. Lay the plasma sheet on its flat side so that the colored liquid will accumulate in the center. Hold the sheet horizontally in your hand and, using your arm as a pendulum, swing the sheet from side to side several times. Observe what happens to the liquid.

Step 6. Lay the plasma sheet on its flat side on a phonograph record turntable. Start the turntable moving. Observe what happens to the liquid.Rotational Acceleration Demonstration Gravity Resultant Acceleration Vector Acceleration (when rotating) Step 7. Experiment with elevating the outer edge of the plasma sheet on the turntable until the acceleration vector produces a distribution of liquid similar to the dispersion observed in step 1.

QUESTIONS:

1. What implications do the plasma sheet demonstrations have for scientific researchers interested in investigating microgravity phenomena? How will Space Shuttle orbiter thruster firings and crew movements affect sensitive experiments?
2. How might acceleration vectors be reduced on the Space Shuttle? Would there be any advantage to the quality of microgravity research by conducting that research on International Space Station?

1. Investigate how scientists measure acceleration vectors in their research.
2. Challenge the students to design a simple and rugged accelerometer that could be used to measure accelerations experienced in a package sent through the U.S. Mail.