Cotton Ball Catapult
Dawn Buchan
1. Title of the Lesson: Cotton Ball Catapult
2. NJ Core Curriculum Content Standards addressed in the lesson.
 5.1.12.B.2 (Mathematical tools and technology are used to gather, analyze, and
communicate results): Build, refine, and represent evidence-based models using
mathematical, physical, and computational tools.
 5.1.12.C.1 (Refinement of understandings, explanations, and models occurs as new
evidence is incorporated): Reflect on and revise understandings as new evidence
emerges.
 5.1.12.D.1 (Science involves practicing productive social interactions with peers, such as
partner talk, whole-group discussions, and small-group work): Engage in multiple forms
of discussion in order to process, make sense of, and learn from others' ideas,
observations, and experiences.
 5.1.12.D.2 (Science involves using language, both oral and written, as a tool for making
thinking public): Represent ideas using literal representations, such as graphs, tables,
journals, concept maps, and diagrams.
 5.2.C (Forms of Energy): Knowing the characteristics of familiar forms of energy,
including potential and kinetic energy, is useful in coming to the understanding that, for
the most part, the natural world can be explained and is predictable.
 5.2.D (Energy Transfer and Conservation): The conservation of energy can be
demonstrated by keeping track of familiar forms of energy as they are transferred from
one object to another.
 5.2.12.D.1 (The potential energy of an object on Earth's surface is increased when the
object's position is changed from one closer to Earth's surface to one farther from Earth's
surface.): Model the relationship between the height of an object and its potential energy.
 5.2.E (Forces and Motion): It takes energy to change the motion of objects. The energy
change is understood in terms of forces.
 5.2.12.E.1 (The motion of an object can be described by its position and velocity as
functions of time and by its average speed and average acceleration during intervals of
time.): Compare the calculated and measured speed, average speed, and acceleration of
an object in motion, and account for differences that may exist between calculated and
measured values.
 5.2.12.E.3 (The motion of an object changes only when a net force is applied.): Create
simple models to demonstrate the benefits of seat belts using Newton's first law of motion.
 5.2.12.E.4 (The magnitude of acceleration of an object depends directly on the strength
of the net force, and inversely on the mass of the object. This relationship (a=Fnet/m) is
independent of the nature of the force.): Measure and describe the relationship between
the force acting on an object and the resulting acceleration.
3. Identify Resources needed.
a. Teacher Use: Meter stick/ tape measure, cotton balls
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b. Student Use: Popsicle sticks, rubber bands, plastic spoons, cardboard cereal boxes, tape,
scissors
4. Describe what students should know before they start the lesson.
 Students should be able to work cooperatively in small groups. They should listen to and
have respect for others' ideas.
 Students should understand the steps involved in the engineering design process.
 This lesson would be part of the unit on work and energy. Students should understand
how energy is transformed between various forms (potential, kinetic).
5. State the objectives of the lesson.
 Students will increase their ability to work cooperatively to solve a problem.
 Students will learn how to use a systematic approach to solving a problem.
 Students will learn about elastic potential energy and how it relates to catapult design.
 Students will learn about air resistance and how it relates to the flight of the cotton ball.
 Students will learn how to use the engineering design process to solve a problem.
 Students will learn that engineering involves using their ideas and knowledge to solve
real-world problems.
 Students will learn about how to balance the cost of materials with the benefits they
provide.
 Students will learn about civil engineering (building structures such as catapults,
theoretically), but also that other engineers are responsible for developing stronger,
cheaper, or more environmentally friendly construction materials. Students will learn
how the work done by engineers affects society for the better. While modern day
engineers don't usually make catapults, they do make toys or other military equipment
that functions similarly.
 Students will apply their knowledge of physics to solve a real world problem.
6. Identify important ideas in terms the subject area - describe in detail. Real life connections
(make a list).
 The engineering problem-solving strategy (which mimics the ISLE cycle for
experimentation) involves devising a series of possibilities that are tested and revised.
 The eight steps of the engineering design process are: identify the need or problem,
research the need or problem, develop possible solutions, select the best possible
solution, draw a prototype, test & evaluate, communicate the solution, and redesign.
 The engineering design process includes constructing a physical prototype: starting with
plans and ideas, using materials to build the physical model. This prototype can then be
tested, and the results applied to redesign and improve. This lesson will involve
numerous iterations of the engineering design process.
 Elastic potential energy: Hooke's Law applies to ideal springs, Elastic potential energy
U= ½ kx2. The plastic spoon or rubber band probably doesn't follow Hooke's Law, but
the concept is still true that more elastic potential energy is stored in the spoon-cotton ball
system when the spoon is bent further from its equilibrium position.
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


Projectile motion: With the assumption that air resistance is negligible, the ideal launch
angle for a projectile is 45 degrees from horizontal in order to have the projectile travel
the maximum distance.
Air resistance: When a projectile is small and has a hard, aerodynamic surface, air
resistance can often be assumed to be negligible. However the cotton ball is very large
and fluffy relative to its mass, so it has relatively large air resistance. Thus students'
predictions of ideal launch angle from concepts of projectile motion (see above) are not
valid.
Torque: When the cotton ball is being launched (spoon or rubber band pulled back), a
backward-directed force is exerted on the catapult which results in an applied torque. If
the catapult doesn't have a rear brace, there will be no object exerting a force that
provides an opposite-direction torque and the catapult will fall over. In order for the
catapult to be stable, both the sum of the forces exerted on it and the sum of the torques
exerted on it must be equal to zero.
7. Describe potential difficulties students may experience with the content. Describe all
formative assessments that you plan to use and how you will provide feedback.
 Students may have difficulty working cooperatively. One group member may dominate,
especially boys in mixed gender groups.
 Students may have difficulty applying the engineering design process, rather than just
employing a trial and error strategy. I will remind the students to plan ahead. Also, I can
present the problem but not make the materials available for the first five minutes, which
will force students to plan (steps 2-5) before building their prototype.
 I will monitor the groups, and make sure to engage group members whose opinions don't
appear to be being listened to. This will demonstrate to the dominating group members
that the others' ideas are to be valued. This also will ensure that all group members are
contributing equally, and that all group members understand the successes and failures of
their prototypes.
 I will ask groups what problems they are having, or what is standing in the way of their
meeting their goals, to engage them in a discussion about the possible strategies they
could employ to solve their problems, rather than just using trial and error. Students may
need to be prompted to systematically change one aspect of their design at a time to solve
the problem.
 I will ask students what assumptions they made in their initial plan that turned out to not
be valid, and how they have revised their assumptions. In this lesson, many assumptions
(air resistance being negligible is one) are definitely NOT valid. I would ask students
how the performance of the catapult might be different if they had a ping pong ball
instead of a cotton ball.
 If a group adopts a new approach, I will ask them to explain what they changed and the
reason for the change. In addition, I will try to get them thinking about the physics
explanation for the failure of their prior prototype.
8. Provide a description of the lesson including an agenda for the lesson.
 See handout attached at end of lesson plan
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9. Time Table – who is going to be doing what and when during the lesson to make sure that
students are actively engaged.
Clock reading
“Title of the
Students doing
Me doing
during the lesson
activity”
0 – 3 minutes
Introduction
Listening
Talking
3 – 10 minutes
Planning
Planning, brainstorming,
Listening, monitoring
discussing ideas
student group work
10 - 40 minutes
Construction,
Constructing the prototype Monitoring student work
Testing,
catapult, testing,
Redesign
redesigning
40 – 50 minutes Testing
Final testing of catapults
Supervising testing
procedure
50 – 60 minutes Reflection
Talking
Listening, summarizing
10. Describe the homework you will assign. What guidance will you provide the students?
 The homework will be for students to assess the strengths and weaknesses of their own
design, and also that of at least one other group, and make at least one suggestion for a
modification they could make that would meet a different need/ solve a different
problem. This engages the students in the engineering design process. Discuss the
homework the next day so students can learn from the ideas of others. Students will be
instructed to think about how real world engineers apply the engineering design process
to the construction of equipment (not necessarily just catapults), and which types of
engineers might work together on the project.
11. Teacher's Guide
 Make sure students are divided into effective groups. Group together students with
differing strengths. Make sure all group members are actively participating.
 Make sure students follow the engineering design process and plan before building.
 Ensure that you are familiar with the materials and their benefits/ pitfalls.
 With the homework, make sure students think about how many different types of
engineers might try to improve the catapult. Materials cost? More environmentally
friendly materials? Performance (distance) enhancement? And so on. Make sure a whole
class discussion of the homework assignment is included in a subsequent class period.
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Cotton Ball Catapult
Goal: Design and build a catapult that meets the design criteria below.
Design Criteria:
 The catapult must be free-standing.
 The catapult must be able to launch a cotton ball at least 30”.
 Only materials listed below may be used.
Testing Criteria:
 You will use your catapult to launch a cotton ball three times and measure the distance
each cotton ball travels. The cotton ball must travel at least 30” on at least one of the
trials.
Challenges:
 Maximize the average distance that the cotton ball travels.
 Maximize the distance-to-cost ratio (the average distance that the cotton ball travels in
inches divided by the cost of your catapult in $).
Available materials and cost:
Material
Quantity Used
Cost per piece
Popsicle stick
$0.10
Plastic spoon
$1.00
Rubber band
$0.25
Cardboard cereal box
$1.00
Tape
$0.25 per foot
TOTAL COST:
Cotton Ball launch distance (inches):
Trial 1: __________ Trial 2: __________ Trial 3: __________
Average distance: __________
Random uncertainty of cotton ball launch distance: __________
Calculation of Distance-to-Cost Ratio:
Average
Distance
Traveled : ____________
Total cost:
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=
_________________
Total (Quantity * Amount)
Be sure to follow the Engineering Design Process and document your work. Notice that there is plenty of
space in the table for you to redesign after testing the prototype!
Step Number
Comments and Observations
1: Identify the
need or problem
2: Research the
need or problem
Initial Design
3: Develop
possible
solutions
4: Select the
best possible
solution
5: Draw a
prototype
6: Test and
evaluate
7: Communicate
the solution
8: Redesign
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