Lesson: Catapult (Testing Exp.)
1. NJ standards addressed in the lesson:
5.1.12.B.1:Design investigations, collect evidence, analyze data, and evaluate
evidence to determine measures of central tendencies, causal/correlational
relationships, and anomalous data.
When launching cotton balls, students will need to think about the assumptions they made
when testing the optimal launching distance. When the ball is not launched as far as they
expect, they will need to look at the data and the concepts they know to understand why it
is so.
5.1.12.B.3: Revise predictions and explanations using evidence, and connect
explanations/arguments to established scientific knowledge, models, and
theories.
AND
5.1.12.C.1: Reflect on and revise understandings as new evidence emerges.
AND
5.1.12.C.2: Use data representations and new models to revise predictions and
explanations.
In addition to revising their knowledge of physics, students will have to repeatedly make
adjustments to the design of their catapult to achieve the goal and solve their problems.
These revisions should not be trial and error, but rather concrete reasoning for the
alterations are necessary and analysis of why the original design did not work is crucial to
the design process.
5.1.12.C.3: Consider alternative theories to interpret and evaluate evidence-based
arguments.
If the outcome of the experiment does not meet expectations, reevaluate assumptions and
revise explanations as part of the engineering redesign process to solve the problems that
arose and complete the task successfully.
5.1.12.D.1: Engage in multiple forms of discussion in order to process, make sense
of, and learn from others’ ideas, observations, and experiences.
AND
8.1.12.C.1: Develop an innovative solution to a complex, local or global problem or
issue in collaboration with peers and experts, and present ideas for feedback in an
online community.
Students will work together in groups (if possible containing individuals of various
strengths and backgrounds) to collectively solve the problem at hand and each contribute
their own knowledge and ability.
5.2.12.E.1: 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.
The kinematic equations for projectile motion only work under ideal conditions (ie. No
wind resistance). This is a key point that students will need to realize and overcome in
constricting their catapult. To prove their understandings, students will need to take and
analyze data to find the optimal launching conditions for their cotton ball.
2. What students should know before they start the lesson:



Basic kinematic equations
Calculating uncertainties
Steps of the engineering design process
3. Goals of the lesson
Content:
Goals
Projectile motion and kinematics
Standards Addressed
5.1.12.E.1
Process:
Goals
Standards Addressed
Understand parts of the Engineering Design Process
8.1.12.C.1, 5.1.12.D.2
Conduct a testing experiment
5.1.12.C.1, 5.1.12.C.3
Systematically make small changes when problems arise
5.1.12.C.3
Epistemological:
Goals
Standards Addressed
Understand why a given solution does not work and come up
with solutions.
5.2.12.E.1, 5.1.12.C.1,
5.1.12.C.3
Analyze what assumptions were made and how they affect
results
5.2.12.E.1, 5.1.12.C.1,
5.1.12.C.3
Learn to appreciate and use others’ abilities and cooperate to
achieve a common goal
5.1.12.D.1, 8.1.12.C.1
Learn the difference between engineering and physics.
5.2.12.E.1, 5.1.12.D.1,
8.1.12.C.1
Metacognitive:
Goals
How can I contribute my strengths to the discussion and help
solve the problem?
Standards Addressed
5.1.12.D.1, 8.1.12.C.1
4. Most important ideas




Aspects of the engineering process: Identify the problem, research the problem (mathematical
approach), develop possible solution, construct prototype, test and evaluate,
Redesign/communicate solution.
Evaluating assumptions and application of theory is not always straight forward.
Addressing problems with design one at a time, not all together
The practical difference between engineering and physics
5. Student potential difficulties:

Understanding why outcome did not match predicted values from mathematical
calculations.
 This is the perfect example of evaluating assumptions. Students need to realize that the
kinematic equations assume NO AIR RESISTANCE. Of course, this works fine for balls,
marbles, etc. but due to the low mass of cotton balls, air resistance is a big factor in their
ability to gain air time.

The actual construction and design process.
Students need to be reminded of the type of difficulties actual engineers have with construction.
Sometimes designs need to be reevaluated if the initial design does not work out as planned and
sacrifices may have to be made in design or construction in order to achieve something similar
to the original design.
ex:
“What is standing in the way of you succeeding with your original design?”
“What do you think is limiting your distance? What is one thing you can do to make it better?”
6. Equipment needed:
Student Use
 Large tongue depressors
 Tape
 Glue
 Cereal boxes
 Plastic spoons
 Rubber bands
 Scissors
 Cotton balls
 Computer
 PhET Projectile Simulation
Teacher use
 Measuring tape
7. Lesson description:
Catapult Design(testing experiment)
Lab Goals:
 Be cautious of assumptions
 Learn to redesign without trial and error
 Find the difference between engineering and physics
The story:
Before we had missiles and unmanned drones, back when people wore brooms on their
heads (think of the Trojans) the best method of long distance attack was the catapult. Your empire
is currently under attack and you are building the secret weapon, the “chicken-maker”. This tactic
involves launching a ball of tar, slowing your enemies, immediately followed by a ball of feathers,
rendering your enemies ridiculous, by way of a catapult. The hope is that after this devious attack,
in their shame, they will give up and retreat.
Being the careful planner that you are, you build scale models of your design to test its
effectiveness. To simulate the tar balls, you use cotton balls wrapped in tape. To simulate the
feather balls you use just regular cotton balls.
Procedure: Follow the steps below and fill in the corresponding sections in the
Engineering/Design Process handout.
a) In ancient times, you would have gone to school for decades to learn about your craft,
however, we only have about 80 min, so in the interest of time, go online to:
http://phet.colorado.edu/en/simulation/projectile-motion
b)
c)
d)
e)
and explore the different variables in projectile motion. Make sure to note specifically what
conditions cause your projectile to go the farthest (angle, initial speed, etc.).
Once you have decided on the criteria that will help you achieve your goal, look at the
materials and think of how you will reach this goal using what is being made available to
you. Draw sketches for possible solutions.
Once you have decided on a plan of attack, show and describe design to your teacher. If you
get the ok, take the materials you need and begin building.
Note any problems you come across in the building process. How did you overcome them?
Test your working catapult with the “Tar Ball” note how far it goes. If necessary, make
adjustments to make it go as far as possible. (Not these in the design process handout).
Tar Ball distance ____________________
f) How did you maximize the distance traveled by the “tar ball”
g) Based off of your “research,” how far should the “feather ball” got in the same conditions as
the “tar ball”?
Feather ball dist. (Predicted) ______________________
h) Test your prediction, how far did the cotton ball go?
Feather Ball dist. (Actual)________________
i) If these two results are not the same, why do you think this happened? What assumptions
do not hold for the cotton ball that were ok for the ball wrapped in tape?
j) Think of the adjustments you can make to overcome these assumptions and do so to launch
your cotton ball as far as possible.
Final Max. achievable distance____________________
Design Process Handout
Step
Notes
1) Problem: What is
your goal?
2) Research/Possible
Soln’s: What
variables will
maximize dist? How
will you achieve
this with given
materials?
3) Best Possible Soln:
Sketch and describe
final design
features
4) Soln. design
features: Note
changes made
during
construction.
5) Construct, test,
and evaluate:
Tar Ball distance _________________
Feather Ball Dist. (Predicted)__________________
Feather Ball dist. (Actual)____________________
6) Communicate
Solution: What
changes did you
have to make to
maximize the
“feather ball”
distance?
7) Redesign: Draw
your final product
with all
measurements.
Max Feather ball dist. Achieved __________________
Teacher Notes:
It is crucial in this assignment that students learn to think of the assumptions made by them
and the simulation they use as the basis of their knowledge. Kinematic equations assume no air
resistance, and even the simulation assumes constant air resistance, when real air resistance is
extremely complicated. Therefore students need to be able to account for these assumptions and
understand how they affect the end result.
It is very easy for students to approach this lab from a “trial and error” perspective. In order to
truly drive home the “design” process, it is the teacher’s job to encourage students to try to plan and
reason as much as possible. Rather than let the futz around with a position for an axel or rubber band
or a stopper to stop the swinging arm, try to get the reasoning out of them and have them realize what
changes will be most effective in helping them launch a cotton ball the farthest. In addition, students
need to realize that when there is a problem that needs to be addressed, one should try to make small
changes to singular problems than one change to many problems or, even worse, decide that nothing
works, take it apart, and rebuild it. Addressing problems systematically is beneficial to the engineering
process and their final goal.
This lab represents an important distinction between physics and engineering. Where physics
explains broad concepts in ideal conditions, engineering takes these concepts, concentrates them, and
seeks to find the assumption that the physicists took for granted and figure out how to overcome them
for a practical purpose.
Finally, it is important for students to realize that the best distance of their cotton ball is not
indicatory of their grade on the assignment. Their grade will depend on the rubrics for a testing
experiment (which they will have access to from the teacher website). So it is their work and accurate
analysis of assumptions and proper reasoning of agreement or disagreement between predictions and
outcomes that will affect their grade for the assignment.
8. Time Table(2 Day lab or 1 day extended period)
Clock reading
during the lesson
0 - 5 min
5-10 min
10-35 min
“Title of the
activity”
Homework quiz,
receive feedback
Introduction,
statement of story
and materials
Initial research and
calculations
35-45 min
Begin designing
45-75 min (0-30 min
if continuing on
another day)
Building and testing
Students Doing
Teacher Doing
Writing
Checking up equipment for
the first activity
Listening taking notes, Addressing class, showing
Getting into groups.
material
PhET simulations,
noting what effects
horizontal distance
Helping students notice that
angle affects distance.
Encouraging students to
take data
Looking at materials
Approving of designs and
and beginning to think helping students realize
about design and how their ideas.
they will achieve their
goal
Constructing
Helping students overcome
catapults, testing
design hurdles. (see
initial ranges and
Possible students
noting changes that
difficulties)
need to be made
Clock reading
during the lesson
70 – 85 min (30-45
min next day)
“Title of the
activity”
Make changes and
evaluate
Students Doing
Teacher Doing
Finishing their design
and hopefully
achieving best results
after considering
assumptions
Helping students overcome
design hurdles. (see
Possible students
difficulties). Encouraging
step by step fixes. Assigning
homework.
9. Formative Assessments:
Content Goals:
 Observe that the angle of the projectile will affect maximum distance
 Correct calculation of uncertainties in average velocity and heights. Outcome reflects
consistency between result and prediction.
Process Goals:
 Detailed completion of the design handout
 Assessment through testing experiment rubrics
 Ability to overcome problems will demonstrate that they are able to address small
problems one at a time rather than tear the whole thing apart and start over.
Epistemological Goals:
 Students’ ability to accurately and effectively analyze assumptions and explain what effect
this had on the distance the various projectiles traveled.
 Ability of students to effectively solve problems and hurdles in the design process.
 Students are able to effectively work in groups and no one individual is doing bulk of work.
 In homework, answers question relating engineering and physics effectively.
Metacognitive Goals:
 Ability to answer homework question on contribution to the team and design process.
10.
Modification for different learners:
By nature of the course, different learners will automatically be accounted for. Students will be
working in groups, so the activity is already a cooperative learning activity. The activity could
utilize technology in the form of graphing or mathematical programs for learners who prefer the
organization of a computerized write-up. Bilingual or ELL students should have no difficulty as they
not only have peer instruction, but all concepts used in the lab have been previously addressed and
students are constructing new knowledge together. Since the teacher is not introducing new terms
or ideas, there is no risk of misunderstanding.
11.
Homework:
1) We saw today that, when we tried applying physics to our real life situation, the physics
failed (Which NEVER happens!) Based on this, what do you feel is the difference
between physics and engineering? What kind of problems do each group have to deal
with and what is their typical approach?
(Students should address how physicists will attempt to simplify the situation to ideal
terms to make the mathematics simpler and develop a model that MOST accurately
describes the situation, whereas engineers, who have to apply the physics in real life, have
to take these models as just models and deal with all the problems that the physicists
simplified away, see “spherical cow” joke…)
2) What difficulties did you have in the engineering and design process ? (List at least two)
How did you overcome these difficulties?
3) What was your contribution to the design process?
4) How would you further improve your catapult? Remember that, technically, according
to the story, you are aiming for both projectiles to land in the same place, but we saw
that they travel different distances on the same setting. How can you fix this problem?