Microgravity In The Classroom
|Objective: · To demonstrate
how microgravity is created by freefall.
Science as Inquiry
- position and motion of objects
Change, Constancy, & Measurement
- evidence, models, & exploration
|Science Process Skills:
Computation & Estimation
MATERIALS AND TOOLS
Various objects demonstrate microgravity as they are dropped
Each demonstration requires a clear space where drop tests can be conducted. Two of the demonstrations require water and you should have a mop, sponges, or paper towels available to clean up any mistakes.
Begin with the Falling Weight apparatus teacher demonstration. Before dropping the device, conduct a discussion with the students to consider possible outcomes. Ask students to predict what they think will happen when the device is dropped. Students will focus on the proximity of the balloon and the needle.
Will the balloon break when the device is dropped? If the balloon does break, will it break immediately or when the device hits the floor? Try to get students with different predictions to debate each other. After the debate, drop the device.
Be sure to hold the wooden frame by the middle of the top cross piece. Hold it out at arm's length in case the weight and needle bounce your way.
Discuss the demonstration to make sure the students understand why the balloon popped when it did. Before trying any of the other demonstrations, student groups should read the student reader entitled Microgravity.
The second and third demonstrations can also be done by the teacher or by small groups of students. One student drops or tosses the test item and the other students observe what happens. Students should take turns observing.
Gravity is an attractive force that all objects have for one another. It doesn't matter whether the object is a planet, a cannonball, a feather, or a person. Each exerts a gravitational force on all other objects around it.
The amount of force between two objects depends upon how much mass each contains and the distance between their centers of mass. For example, an apple hanging from a tree branch will have less gravitational force acting on it than when it has fallen to the ground. The reason for this is because the center of mass of an apple, when it is hanging from a tree branch, is farther from the center of mass of Earth than when Iying on the ground.
Although gravity is a force that is always with us, its effects can be greatly reduced by the simple act of falling. NASA calls the condition produced by falling microgravity.
You can get an idea of how microgravity is created by looking at the diagram. Imagine riding in an elevator to the top floor of a very tall building. At the top, the cables supporting the car break, causing the car and you to fall to the ground. (In this example, we discount the effects of air friction on the falling car.) Since you and the elevator car are falling together, you feel like you are floating inside the car. In other words, you and the elevator car are accelerating downward at the same rate due to gravity alone. If a scale were present, your weight would not register because the scale would be falling too. The ride is lots of fun until you get to the bottom.
NASA uses several different strategies for conducting microgravity research.
NASA has several drop tower facilities including the 145 meter drop tower at the NASA Lewis Research Center in Cleveland, Ohio. The shaft is 6.1 meters in diameter and packages fall 132 meters down to a catch basin near the shaft's bottom. For 5.2 seconds, the experiment experiences a microgravity environment that is about equal to one one-hundred-thousandth (lx10 -5 ) of the force of gravity experienced when the package is at rest.
If a longer period of microgravity is needed, NASA uses a specially equipped jet airplane for the job. Most of the plane's seats have been removed and the wall, floor, and ceiling are covered with thick padding similar to tumbling mats.
One of the advantages of using an airplane to do microgravity research is that experimenters can ride along with their experiments. A typical flight lasts 2 to 3 hours and carries experiments and crew members to a beginning altitude about 7 kilometers above sea level. The plane climbs rapidly at a 45-degree angle (pull up) and follows a path called a parabola. At about 10 kilometers high, the plane starts descending at a 45-degree angle back down to 7 kilometers where it levels out (pull out). During the pull up and pull out segments, crew and experiments experience a force of between 2 g and 2.5 g. The microgravity experienced on the flight ranges between one one-hundredth and one one-thousandth of a g. On a typical flight, 40 parabolic trajectories are flown. The gut-wrenching sensations produced on the flight have earned the plane the nickname of "Vomit Comet."
Small rockets provide a third technology for creating microgravity. A sounding rocket follows a parabolic path that reaches an altitude hundreds of kilometers above Earth before falling back. The experiments onboard experience several minutes of freefall. The microgravity environment produced is about equal to that produced onboard falling packages in drop towers.
Although airplanes, drop facilities, and small rockets can be used to establish a microgravity environment, all of these laboratories share a common problem. After a few seconds or minutes of low-g, Earth gets in the way and the freefall stops. When longer term experiments (days, weeks, months, and years) are needed, it is necessary to travel into space and orbit Earth. We will learn more about this later.