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TE Activity: Catapults!

Students observe the relationship between the angle of a catapult (a force measurement) and the flight of a cotton ball. They learn how Newton's second law of motion works by seeing directly that F = ma. When they pull the metal "arm" back further, thus applying a greater force to the cotton ball, it causes the cotton ball to travel faster and farther. Students also learn that objects of greater mass require more force to result in the same distance traveled by a lighter object.

Understanding the scientific concepts of Newton's laws of motion has made it possible for engineers to build airplanes that fly, elevators and amusement park rides that are exciting but safe, cars that drive safely at high speeds and structures that do not collapse. Aerospace engineers save fuel by exploiting the second law when they let the planet's force of gravity pull a spacecraft towards the planet to increase its velocity, and then steer the spacecraft away from crashing into the planet.

Learning Objectives
Materials
Introduction/Motivation
Procedure
Attachments
Safety Issues
Troubleshooting Tips
Assessment
Extensions
Activity Scaling
References

Grade Level: 6 (5-7)	Group Size: 4
Time Required: 50 minutes	Activity Dependency : None
Expendable Cost Per Group : US$ 5
Keywords: mechanics, Newton, acceleration, catapult, force, graphing, laws of motion, mass, motion

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Colorado Math
- 1. represent, describe, and analyze patterns and relationships using tables, graphs, verbal rules, and standard algebraic notation; (Grades 5 - 8) [2005]
- 1. read and construct displays of data using appropriate techniques (for example, line graphs, circle graphs, scatter plots, box plots, stem-and-leaf plots) and appropriate technology; (Grades 5 - 8) [2005]
- 1. demonstrate meanings for integers, rational numbers, percents, exponents, square roots, and pi (π) use physical materials and technology in problem-solving situations; (Grades 5 - 8) [2005]
- 1. estimate, use, and describe measures of distance, perimeter, area, volume, capacity, weight, mass, and angle comparison; (Grades 5 - 8) [2005]
Colorado Science
- Standard 1: Students understand the processes of scientific investigation and design, conduct, communicate about, and evaluate such investigations. (Grades 0 - 12) [1995]
- Standard 5: Students know and understand interrelationships among science, technology, and human activity and how they can affect the world. (Grades 0 - 12) [1995]
- 2.1 Students know that matter has characteristic properties, which are related to its composition and structure. (Grades 0 - 12) [1995]
- 2.2 Students know that energy appears in different forms, and can move (be transferred) and change (be transformed). (Grades 0 - 12) [1995]
- 2.3 Students understand that interactions can produce changes in a system, although the total quantities of matter and energy remain unchanged. (Grades 0 - 12) [1995]

After this activity, students should be able to:

Understand Newton's second law, that force is equal to the mass times the acceleration (F = ma).
Predict the results of using a greater force or attempting to accelerate a greater mass.
Use number sense by correlating the number on the protractor to an angle.
Use the catapult model to explore the angle of the protractor to the force exerted on the cotton ball, graph the correlation between angle (force) and distance traveled (acceleration).
Collect data throughout this experiment, including the maximum height of the cotton ball in flight and the distance traveled until it lands on the floor.
Use geometry (the various angles of the protractor) and correlate this geometric angle to the magnitude of force exerted on the cotton ball.
Calculate the average of a data set.

Catapults were first used around 400 BC in ancient Greece and China as a weapon to launch rocks, arrows and other projectiles against enemies. In the centuries after their first appearance, bigger and bigger catapults were constructed. Over time, catapults were made so big that they became too difficult to use, and eventually were no longer used. However, the fundamental concepts used In a working catapult are still in use every day. Engineers need to understand how much force is required to make an object with a certain mass move. Catapults are one good way to learn about the relationship between force, mass and acceleration. The relationship F = ma is called Newton's second law of motion because Sir Isaac Newton mathematically described the relationship among force, mass and acceleration.

Before the Activity

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Gather materials.
Choose appropriate locations for students to fire their catapults.

With the Students

Open with a discussion question: Has anyone ever seen or built a catapult? How does it work? Tell the students that we will find out more about this in today's activity.
Hand out a worksheet to each student.
Bend the metal banding into an L shape and insert the "L" end between the two wooden blocks (see diagram).
Hold the blocks in place by one of three options: Nail the blocks together by hammering two nails on either side of the metal stripping. Or, use a C-clamp or duct tape to hold the blocks together securely.
Tape the protractor vertically to the front of the catapult, close to the metal band (arm).
Ask students make predictions (hypotheses) of what angle of the catapult will make the cotton ball travel highest and furthest.
Once the catapult is built, assign roles to each team member. Instruct one student to fire the cotton ball, one to spot the maximum height of the cotton ball when in flight, one to spot the landing point where the cotton ball first hits the ground, and two to measure the height and distance of flight.
Place cotton ball at the end of the arm.
Pull the metal band (arm) back 10 degrees and release. If it flies straight up or backward, fire again. Conduct two trials.
Have students record their measurements on the worksheet, as they proceed through the activity.
Repeat firing process at 20 degrees through 90 degrees.
Have students complete the rest of the worksheet.
While waiting for other students to finish worksheets, students with completed worksheets should compare their answers with their peers.
Review worksheet answers with students.

Newton's Second Law - Catapult Worksheet

Pre-Activity Assessment

Discussion Questions: Solicit, integrate and summarize student responses.

Has anyone ever seen or built a catapult? How does it work?

Activity Embedded Assessment

Worksheet: Have the students record measurements and follow along with the activity on their worksheet. After students have finished their worksheet, have them compare answers with their peers.

Post-Activity Assessment

Worksheet Discussion: Review and discuss worksheet answers with the entire class. Use the answers to gauge students' mastery of the subject.

Integrated Teaching and Learning Program, College of Engineering, University of Colorado at Boulder Sabre Duren, Ben Heavner, Malinda Schaefer Zarske, Denise Carlson © 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.

Last Modified: April 27, 2006