TE Activity: Action-Reaction! Rocket
Contributed by: Integrated Teaching and Learning Program, College of Engineering, University of Colorado at Boulder
Summary |
Engineering Connection |
| Engineers of all disciplines use their understanding Newton's laws of motion to quantify the "invisible" forces acting on all objects. Just like a ball can be twirled on the end of a string, satellites and spacecraft stay in orbit around the Earth due to the balance between gravitational and centripetal forces. Eventually, satellites slow down due to the miniscule drag in the upper atmosphere, to the point at which gravity pulls them out of orbit. To keep them in orbit, engineers exploit the second law by designing thrusters that burn fuel and expel it from the thruster. The spacecraft moves forward in an amount equal to the force of the gas leaving the thruster, causing enough movement to re-orient the path of the object and keep it in orbit. |
Contents
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| Grade Level: 6 (5-7) | Group Size: 4 |
| Time Required: 45 minutes |
Activity Dependency  :None |
Expendable Cost Per Group
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US$ 1 |
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| Keywords: mechanics, Newton, acceleration, balloon, force, laws of motion, mass, motion, rocket | |
| Reviews: Read Reviews | Be the First to Write a Review | |
Related Curriculum
:
| subject areas | Physical Science Physics |
| curricular units | Mechanics Mania |
| lessons | Motion Commotion |
Learning Objectives (Return to Contents)
After this activity, students should be able to:
- Understand how Newton's first law of motion relates to the activity. (At the beginning of the activity, the rocket remains at rest until the force of the escaping air makes it move. After the air is released, friction from the string brings the rocket to a stop.)
- Understand how Newton's second law of motion relates to the activity. (When the air is released from the balloon, it exerts a force that sets the rocket into motion. The motion of the rocket depends upon the size of the force and the mass of the rocket.)
- Understand how Newton's third law of motion relates to the activity. (Air escaping from the balloon [an action] causes motion of the rocket [a reaction])
- Use number sense to understand that the action force is equal to the reaction force.
- Use the model of the balloon to understand that the size of balloon, dependent on the amount of air in the balloon, decreases or increases the action/reaction that is produced when the air is released.
- Measure the distance the balloon travels along the string, representing the reaction force.
- Collect data on the different sizes of the balloon (depending on how much air is in it), how far the balloon travels along the string, and graph the results.
Materials List (Return to Contents)
For each group:
- Plastic drinking straw
- Plastic bag, about the size of an inflated balloon
- Paper streamers
- 25 ft. of fishing line (20-50g weight) or string (nylon [slippery] string works better than twine [rough])
- Long, tube-shaped balloon
- Tape measure or meter stick
Introduction/Motivation (Return to Contents)
Start with an in-class demonstration. For example, have a student or the teacher stand on a skate board and throw a basketball. What happens? Have a student or the teacher throw a basketball filled with lead weights or similar, very heavy object (this could be dangerous; be very careful not to fall). What happens? (Answer: The student or teacher rolls backwards on the skateboard.)
Or, as another demonstration: Pass around three containers (such that students cannot see the contents), one filled with something light such as feathers, one filled with something heavy such as lead weights and one filled with something in the middle such as rice or grains. Ask students which one is heavier. Ask them what they think is inside. Tell them that the heaviest one is heavier because it has a higher mass.
Rockets and rocket-propelled flight has been in use for more than 2,000 years. People in ancient China used gunpowder to make fireworks and rockets. In the past 300 years, people have gained a scientific understanding of how rockets work. Now, aerospace engineers use their understanding to make rockets fly farther, faster, higher and more accurately. Our understanding of how rockets work arises from Sir Isaac Newton's three laws of motion. It is important for engineers to understand Newton's laws because they not only describe how rockets work, they explain how everything that moves or stays still works!
This activity demonstrates all three of Newton's laws of motion. The focus of the activity is Newton's third law of motion, but the first and second laws are intrinsically involved with the motion of the rocket as well. The air pushing its way out of the balloon is an action force, and it causes an equal reaction, which is the movement of the balloon. The more air initially in the balloon, the further the balloon travels along the string because the action force is greater. By the same token, if there is only a small amount of air initially in the balloon, the balloon travels a shorter distance.
Simply stated, Newton's three laws of motion are:
Law #1: Objects at rest will stay at rest, and objects in motion will stay in motion in a straight line unless they are acted upon by an unbalanced force. (law of inertia)
Law #2: Force is equal to mass multiplied by acceleration. (F = ma)
Law #3: For every action, there is always an opposite and equal reaction.
Procedure (Return to Contents)
Before the Activity
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Action-reaction rocket activity set up. click for copyright |
- Gather materials.
- Choose appropriate locations for students to set up the experiment.
With the Students
- Have students vote on which of Newton's three laws of motion applies to the flight of rockets. Tabulate votes on the board. (Answer: Trick question! All three laws apply.)
- Hand out a worksheet to each student.
- Tape a drinking straw along the side of a plastic bag (see diagram).
- Tape streamers along the open edge of the plastic bag.
- Thread the string through the straw.
- Tie each end of the string to a chair, and pull the chairs apart so that the string is taut (see diagram).
- Position the bag at one end of the string, with the open end of the bag facing toward the chair.
- Blow up a balloon and put it into the bag, holding the balloon closed.
- Count down to zero, and let go of the balloon. . . ZOOMMM!
- Have students measure the distance their balloon rocket traveled on the string and complete the worksheet.
- While waiting for other students to finish their worksheets, students with completed worksheets should compare their answers with their peers.
- Review and discuss the worksheet answers with students.
Attachments (Return to Contents)
Safety Issues (Return to Contents)
Straws make excellent projectile shooters. Make sure to collect them at the end of the activity.
Troubleshooting Tips (Return to Contents)
Be sure the students blow up their balloon to different sizes — small, medium and large — to compare the different magnitudes of reaction that are produced.
Thicker fishing line (20-50g) works best for this activity. Next best is nylon string. Rough string or twine creates too much friction for the balloon to travel as far.
The string should be pulled taut for the balloon rocket launch. A slack string does not allow the balloon to travel as far.
This activity can also be done without the plastic bag by taping the straw directly to the balloon. In this case, use large round balloons instead of long balloons.
Assessment (Return to Contents)
Pre-Activity Assessment
Voting: Ask the students vote on which of Newton's three laws applies to the flight of rockets. Tabulate votes on the board. Give answer: Trick question! All three laws apply.
Activity Embedded Assessment
Worksheet: Have the students follow along with the activity on their worksheet. After students have finished their worksheet, have them compare answers with their peers. Review their answers to gauge their mastery of the subject.
Post-Activity Assessment
Numbered Heads: Have the students on each team pick numbers (or number off) so each member has a different number. Ask the students questions from the worksheet. The members of each team should work together on the question. Everyone on the team must know the answer. Call a number at random. Students with that number should raise their hands to answer the question. If not all the students with that number raise their hands, allow the teams to work a little longer. Have students include terms that they have learned in the answers to the questions.
Flashcards: Have each group of students make three flash cards with a question on one side and the answer on the other. In writing the questions and answers, have students incorporate the new terms that they have learned. Have students pass the cards to the group next to them answer the questions and then pass them along. Some example questions include:
- What is inertia? (Answer: When an object is at rest or in a constant state of motion.)
- How are action and reaction forces related? (Answer: They are equal.)
- If acceleration = 6 m/s2 and mass = 6,254 g what is the force? (Answer: 37,524 Newtons [gm/s2].)
- What would happen if you changed the direction of the force (i.e., the balloon blew out toward the floor)? Would the balloon travel a shorter distance, longer distance or the same? (Answer: The balloon would travel a shorter distance if it moves at all, because it would not be able to travel in the direction opposite the force.)
- According to Newton's third law, how do you know that the action and reaction forces on the balloon are equal? (Answer: Because for every action there is an equal and opposite reaction.)
- What vocabulary word would best describe your experience when you are a "couch potato"? (Answer: Inertia.)
- If an equal forces is applied to a Mini Cooper and a semi trailer truck, which will have greater acceleration? (Answer: A Mini Cooper, due to its smaller mass.)
- What does acceleration depend on? (Answer: Mass and force.)
- If you kick two balls that weigh the same, which ball will go further? (Answer: The ball that you kick harder.)
- Does air have mass? (Answer: Yes. It can be measured on a scale.)
- Does Newton's third law work horizontally? (Answer: No. Try it.)
- When mass is multiplied by acceleration, what results? (Answer: Force.)
Activity Extensions (Return to Contents)
Run the experiment with a bigger or smaller balloon.
Have the students fill up their balloons with water and repeat the experiment. Ask them why the balloon moved so slowly (if at all) and why. (Answer: Because the water is heavy, it takes more force to move water than air, and the water spills out of the balloon slowly (compared to air), therefore the reaction force is equally as slow as the action force. Note: This is messy! Make sure you follow the water-balloon with a bucket to catch the water or do this activity outside.
Tape pennies to the outside of the rocket to increase the mass. How does increased mass affect the flight of the rocket? (Answer: Because of Newton's second law, the same force exerted upon a larger mass will result in a lower acceleration - the rocket will not go as far!)
Have the students re-engineer their balloon rockets again, adding extra features to make the balloon go further. Allow them to use more straw and tape, and more than one balloon. Conduct a race to see which engineering team built the best balloon rocket. Ask that team to explain why their design worked as it did, in terms of Newton's three laws of motion.
Ask the students to write a journal entry on how the balloon rocket experiment could relate to something else they've encountered. Why are Newton's laws of motion so important in our world?
Activity Scaling (Return to Contents)
- For lower grades, complete the worksheet as a class, with different groups using different sized balloons. Use the data from each group's work to construct a plot together, as a class.
- Give older students all materials except the worksheet that tells them how to put the rocket together. Ask them to figure out on their own how to construct the rocket.
References (Return to Contents)
Hauser, Jill Frankel.Gizmos and Gadgets: Creating Science Contraptions that Work (and Knowing Why). Charlotte, VT: Williamson Publishing, 1999. (Activity adapted from Hauser.)
NASA Quest > Space Team Online: http://quest.nasa.gov/space/teachers/liftoff/newton.html.
Contributors
Sabre Duren, Ben Heavner, Malinda Schaefer Zarske, Denise CarlsonCopyright
© 2004 by Regents of the University of Colorado.The contents of this digital library curriculum were developed under a grant from the Fund for the Improvement of Postsecondary Education (FIPSE), U.S. Department of Education and National Science Foundation GK-12 grant no. 0226322. However, these contents do not necessarily represent the policies of the Department of Education or National Science Foundation, and you should not assume endorsement by the federal government.
Supporting Program (Return to Contents)
Integrated Teaching and Learning Program, College of Engineering, University of Colorado at BoulderLast Modified: September 26, 2008