Orbits
Grade Level:
7
Time Required:
2 class periods
Countdown:
1 large fruit can (29 oz. size)
Medium Nail
String/Twine
Red or Blue Sand
2 Chairs
1 White Poster Board
1 medium Apple
Duct Tape
1 Fork
Suggested TEKS:
7.13
7.2
Suggested SCANS:
Information. Acquires and evaluation information.
National Science and Math Standards
Science as Inquiry, Earth & Space Science, Physical Science,
Observing, Communicating
Science Art -
Hammer
Scissors
Light Sand (from store)
Meter Stick
Freezer Tape (or other sticky tape)
5 ft. sturdy string
Spool with hole wider than string thickness
Ignition:
An orbit is defined as the path of any object in space whose motion is controlled by the
gravitational pull of a heavier object. The heavier object is called the primary and the lighter
object is the secondary. As an example, the moon is a secondary that revolves in an orbit around
the Earth, a primary.
The sun, a primary, has such an immense gravitational pull that it holds together the nine
planets of our solar system. The planets hurtle through space at speeds that just balance the
sun’s gravitational pull; therefore, they are locked into a perpetual orbit around the sun.
The orbit shape of the planets is generally elliptical – sometimes, the planets are closer to
the sun and sometimes farther away.
Liftoff:
A. Elliptical orbits through sand painting.
This experiment will utilize the swinging motion of a pendulum to make a pattern of
ellipses. Because sand is used, it is recommended that this activity be conducted on a flat
concrete surface outside.
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1. Carefully using the hammer and nail, punch a hole in the bottom of the fruit can.
Then, punch 3 holes in the top edge of can, equally spaced.
2. Cut 3 short pieces of string (about 5 inches long). Tie and knot each one through the
holes in the can’s rim. Pull together the 3 loose ends and tie into a knot. Then, tie a
10-inch piece of string, and loop it around this knot. See diagram below.
5" piece of string
10" piece of string
3. Set 2 sturdy chairs opposite each other, back to back, about ¾ m apart. Place the
meter stick between the chairs, on the chair seats, and secure with a weight, if needed.
See Diagram B.
4. Tape the bottom hole of the can with freezer tape, and fill the can with dry colored
sand. Tie in the middle of the suspended meter stick.
5. Put the poster board on the floor between the 2 chairs, and sprinkle it lightly with
white sand. Tilt the can slightly to one side, remove the tape on the bottom to release
the sand, and gently push the can.
6. You may need to give the string near the can additional pushes, back and forth and to
the sides, until all the sand has drained out.
Meter stick
Durable chair
poster board
SpaceExplorers http://www.tsgc.utexas.edu/spaceexplorers/
Orbital Mechanics: Orbits
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133
Conclusion: The sand being released from the can makes a series of arcs and ellipses on the
poster board.
B. Experiment with planet orbit
This experiment is initiated by the question “Why do planets stay in orbit around the sun?
Why don’t they just spin off into space?”
1. Tie one end of the string around the apple, and knot it tightly. Use the tape to secure
the string tautly around the apple.
2. Push the unattached end of the string through the spool hole and, then, tie it around the
fork. Tape the string securely.
apple with string taped in place
spool
Fork tied to sting end
5 ft. string
3. In an open area, hold the spool with the apple directly on top of it. The remaining
string with the fork is hanging out of the spool, pointing toward the floor. Then, twist
your wrist, sending the apple into orbit.
Results:
The apple remains “in orbit” around you, rather than hurtling off into space.
Conclusion: Elicit from the students what part of the experiment acted like gravity. Also, ask
what would have happened if the string were not tied to the fork. Compare this experiment with
the nine planets and their continuous orbit around the sun.
SpaceExplorers http://www.tsgc.utexas.edu/spaceexplorers/
Orbital Mechanics: Orbits
Texas Space Grant Consortium http://www.tsgc.utexas.edu/
134