How do I Teach Gravity & Orbit Activity?

Engine thrust allows spacecraft to escape the orbital pull of Earth's gravity.

Teaching a hands-on gravity and orbit activity provides a clear demonstration of astronomy concepts that are difficult for children to visualize. Drawing on observations of earth orbit and how the force of gravity works, teachers can guide students to discover how satellites stay in orbit and how spacecraft break free of gravitational orbit to reach their destination.

Things You'll Need

• 1 balloon per group
• 1 stopwatch per group (although you can structure the activity to work with just one if you don't have enough for every group)
• Water
• 5 feet of twine per group
• 1 clothes pin per group
• 1 clipboard per group
• Data collection worksheet
• Plastic bucket
• pencils
• 1 calculator per group

Instructions

Background and Planning

1. Track and record the path of the sun starting early in the school year and discuss how shadow lengths relate to the changing seasons caused by the earth's orbit around the sun. The Smithsonian Astrophysical Observatory provides useful Earth orbit activities.

2. Elicit student understanding of what holds things up and keeps satellites in orbit. "Is There Gravity in Space?" offers helpful gravity and trajectory demonstrations.

3. Tie a 5-foot length of twine securely onto the clothes pins.

4. Fill balloons with water until they are approximately 2 inches in diameter. Make enough for each group and spares. Place them in a plastic bucket.

5. Locate a large, open, outdoor area where students can spread out in small groups at least 20 feet apart.

Activity Procedure

1. Divide the class into groups of three to five. Assign or allow each group to choose a data recorder and a timekeeper. Give the data collection worksheet and clipboard to the data recorder and ask her to bring pencils. Give the timekeeper a stopwatch.

2. Explain that in this activity one student represents a planet, the water balloon an orbiting satellite and the string the force of gravity. They will each have a turn being the planet. Review safety rules and water balloon etiquette.

3. Give each group a water balloon and tell them to clip it securely onto the clothes pin. Remind them not to start swinging it yet. Ask students to predict what they think will happen if they swing the water balloon in a circular motion, slowly, and then faster and faster.

4. Tell other students to stand well back while the timekeeper starts the stopwatch and the first student slowly swings the balloon around his body, "so the balloon is moving just fast enough to keep the balloon a few feet above the ground," advises TeachEngineering. Count how many complete orbits the balloon makes in 10 seconds. The data recorder writes this number on the data collection sheet. Allow each student to repeat the experiment at this speed and record the data.

5. Repeat the swinging procedure three or more times, speeding up slightly on each round, until the balloon breaks loose from the clothes pin.

6. Calculate the escape velocity of each student's satellite planet. TeachEngineering notes the formula: Divide the number of orbits at the final speed by 10 seconds. Then multiply the result times 10 feet (orbital diameter) times pi (3.14). Discuss how the space shuttle must achieve escape velocity in order to break free of earth orbit to reach the space station.

7. Hold a game show style science challenge among the groups. Give each group a gravity- and orbit-related question by turns. They must answer in less than one minute. If they cannot answer the question, the other groups get a chance to answer and steal the points.

Tips & Warnings

• Teachers may find it helpful to cover basic forces and motion before teaching a lesson on gravity and orbit.

• TeachEngineering notes that this activity can also be done with a Wiffle or sponge ball that weighs around 100 grams.

• Water balloons and kids are a recipe for getting wet. Do this activity on a warm day and warn kids ahead of time that they might want to bring a change of clothes, just in case.

• TeachEngineering warns that turning the whole body while swinging the balloon or ball can result in dizziness and falls and recommends swinging the satellite object with an overhead lasso motion.

References

• TeachEngineering: Integrated Teaching and Learning Program: College of Engineering: University of Colorado at Boulder: The Great Gravity Escape: Geoffrey Hill, Daria Kotys-Schwartz, Chris Yakacki, Malinda Schaefer Zarske and Janet Yowell
• Science and Children: National Science Teachers Association (NSTA): Is There Gravity in Space?: Varda Bar, Cary Sneider, and Nathalie Martimbeau: April 1997
• Smithsonian Astrophysical Observatory: Eyes on the Sky, Feet on the Ground: The Earth's Orbit: Christine Jones, Ph.D, Tania Ruiz, Sara Waters and Jeffrey Breen

Resources

• Columbia Education Center: Flight Paths of Orbiting Satellites: Katherine Beal: CC Meneley Elem: NV
• Cornell University: Ask an Astronomer: The Earth
• Smithsonian Astrophysical Observatory: Eyes on the Sky, Feet on the Ground: Jones,Ruiz,Waters, Breen
• Technology Teacher: International Technology Education Association: Chasing Down a Satellite: Diane Fisher: December 2002/January 2003
• Technology Teacher: International Technology Education Association: Launch a Frisbee into Orbit: Diane Fisher, Tony Phillips, and Gene Schugart: April 2003