Hawai'i Space Grant Consortium, Hawai'i Institute of Geophysics and Planetology, University of Hawai'i, 1996
From Microgravity NASA EG-103
by Gregory Vogt
To make a simple accelerometer to measure "G-forces" when you change your motion.
Suddenly, your stomach feels like it's in your throat. Then your body is squashed downward into the seat. You start to climb back up and suddenly you're thrown to the left, then to the right. Are you in some kind of torture machine? Sort of. It's really just a roller coaster!
As your roller coaster car goes up and down and makes sharp turns, your body feels the same forces that astronauts feel as they travel into space. These are called "G" forces. "G" stands for "gravity." Each time you change direction or speed, it feels as though the pull of gravity has changed. Sometimes the pull is more and sometimes less. But the gravity you feel on a roller coaster isn't really changing. It just feels like it does.
Another good example of when it seems like gravity has changed is when you dive off a diving board. As you reach the top of your dive, you feel "weigthtless," as though gravity had disappeared. But suppose you do a bellyflop? The full force of your fall will make it seem like gravity has gotten much stronger. (Ouch!)
When astronauts travel into space, they feel those same forces. During liftoff, astronauts are pulled back into their launch seats. It feels as though gravity has gotten much stronger. (Some astronauts say it feels like an elephant is sitting on their chest!) When their spaceship is in orbit, it's like when you're at the top of your dive. Gravity feels like it has disappeared. When their spacecraft reenters (comes back through) the Earth's atmosphere, it feels like gravity has gotten much stronger again. Like your bellyflop!
It's easy to measure the "G-forces" you feel when you change your motion if you have an accelerometer. Here's how you can make one. Gather the following materials.
- a cardboard tube (one from a roll of wax paper works well or a small mailing tube)
- two rubber bands
- three lead fishing sinkers (1/2 to 1 ounce each)
- masking tape
- marker pen
- Cut out a rectangular-shape window from the cardboard tube that is about
3/4" wide and 8" long. If the tube is about 12" long, then the window will be cut about two inches in from either end. Then trace the end of the tube on the flat sheet of cardboard and cut the circle out. Cut out another circle the same way and tape one circle to each end of the tube.
- Cut each rubber band in half and tie both rubber bands together. Punch a small hole in the middle of the cardboard circles at each end of the tube. Thread an end of the rubber band through each hole and knot it.
- Attach one sinker to the middle of the rubber band in the tubed. Stand the tube upright and mark the side of the tube where the sinker stays as "1-G."
- Temporarily attach a second sinker to the first. The second sinker should pull the rubber bands down farther. Mark the new position of the sinkers as "2-G." Now add the third sinker and mark the new position as "3-G." Remove the second and third sinkers.
- Turn the tube upside down and attach the sinkers the same way you did before. But this time mark the sinker positions as "minus 1-G," "minus 2G," and "minus 3-G."
- At the middle of the tube, halfway between "1-G' and "minus 1-G", mark the position "0=G."
- Remove the two temporary sinkers. Your accelerometer is finished. Ready to try it?
- Hold the accelerometer upright in front of you and jump up as high as you can. What happened to the position of the sinker as you jumped up and came down?
- How many G-forces did the accelerometer say you felt?
- Try using the accelerometer on a fast elevator - or better yet, on your favorite roller coaster. Remember, these are the same G-forces astronauts feel as they rocket into space.
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