Lesson: Solar Car Gear Box (Application Exp.)
1. NJ standards addressed in the lesson:
5.1.12.A.1: Refine interrelationships among concepts and patterns of evidence
found in different central scientific explanations.
Students will be using their knowledge of torque to construct an effective solar car. Since
power output is limited, as engineers it will be their “job” to use the science they know to
get the most out of the solar motor.
5.1.12.A.2: Develop and use mathematical, physical, and computational tools to
build evidence-based models and to pose theories.
Students will have to conduct side experiments to reason mathematically and scientifically
how the motor behaves. Uncertainty and assumptions will play a part in accurate results.
This will then be applied to the actual construction of the vehicle.
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.
5.1.12.D.2: Represent ideas using literal representations, such as graphs, tables,
journals, concept maps, and diagrams.
Students will follow protocol similar to real engineering in which they must present their
final product and defend why their choice of gears and design is the best.
2. What students should know before they start the lesson:
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Circular motion and kinematics
Torque/ Circular dynamics
How to calculate Uncertainty
Static friction (rolling friction)
3. Goals of the lesson
Content:
Goals
Calculate torque and apply findings to solve a problem
Standards Addressed
5.2.12.A.1, 8.1.12.C.1
Numerically observing effects of uncertainties on data
5.1.12.A.2
Process:
Goals
Standards Addressed
Understand parts of the Engineering Design Process
8.1.12.C.1, 5.1.12.D.2
Conduct an application experiment
5.1.12.A.1, 5.1.12.A.2
Epistemological:
Goals
Standards Addressed
How to apply calculated values to real situations
5.1.12.A.1, 5.1.12.A.2
Analyze what assumptions were made and how they affect
results
5.1.12.A.1, 5.1.12.A.2
Learn to appreciate and use others’ abilities and cooperate to
achieve a common goal
5.1.12.D.1, 8.1.12.C.1
Use graphical tools to present evidence of success or a superior
product.
5.1.12.D.2
Metacognitive:
Goals
Standards Addressed
How can I contribute my strengths to the discussion and help
solve the problem?
5.1.12.D.1, 8.1.12.C.1
How can I show that my solution is valid and will work
successfully?
5.1.12.D.2
4. Most important ideas
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Use mathematical evidence to show reasoning and why your solution is the best.
The purpose and application of gears as a simple machine
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.
Account for uncertainty
5. Student potential difficulties:

Understanding why outcome did not match predicted values from mathematical
calculations.
 Although gears are effective tool for transfer of torque, there are other forces aside from
just the mass of the cart that will oppose the torque. Friction between axels, slipping gear
contacts, etc. As such, when students are making calculations to predict the amount of
torque necessary to move the car, some uncertainty will need to be accounted for.
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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 or money in
order to achieve something similar to the original design.
ex:
“What is standing in the way of you succeeding with your original design?”
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Presentation of Ideas in an effective way that conveys a good product.
 Students will need to use graphs and tables to show that they have created the most
effective solar car. This may involve showing data to show that they maximized torque by
showing calculations of torque with corresponding gear sizes. Also Students will have to
show that they have the fastest car. This will have to be done by giving time trial data.
Effective and easy to read data tables and graphs will be integral to this process and
students will need to be reminded of what makes a good table or graph.
6. Equipment needed:
Student Use
 Complete Solar Car kit
o Solar panel
o Gears
o Motor
o Axels
o Wood panel
o Wheels
o Eye screws
 String
 Objects of different mass
 Tape
Teacher use
 White boards or big paper for presentations
 Balance or Scale
7. Lesson description:
Solar Car Gear Box(Application experiment)
Lab Goals:
 Apply mathematical reasoning to construction of a working apparatus
 Understand engineering and design process
 Present information in an effective and convincing way
Your task:
In an attempt to create a new alternative-energy vehicle, an engineering firm has decided to
research getting the most out of a single solar engine in hopes of cutting costs of adding more solar
panels. In order to do this, gears have to be used to maximize the torque transferred from the motor
to the wheels to move the car. This is where you come in. It is your task to find the best combination
of gears to make a functional solar car.
The firm has requested groups of researchers present their findings at the next Solar Car
Summit. This means that groups will have to acquire data showing how effective their designs are
using any method they can (mathematical reasoning, tables, graphs, diagrams, etc).
Design Criteria
1) Design must include only ONE MOTOR and ONE SOLAR PANEL.
2) Make a car that can travel as fast as possible while still using maximum torque efficiency. In
other words, the mass of the car does not slow it down and the wheels do not spin so fast
that they do not grip the ground (Think of static friction).
Presentation Criteria: Presentation must include:
 Maximum predicted load (mass)with calculations
 Time trials to show maximum velocity (without load)
 Car design
 Reasoning for choice of gears (Torque transfer calculations)
 Final Gear ratio (“Number of turns wheels do”: “number of turns motor does”)
Procedure: Follow the steps below and fill in the corresponding sections in the
Engineering/Design Process handout.
a) Before you can start designing your car, you need to find the maximum torque of the solar
motor you are required to use. Since you are required to make the best of the given
technology, you need to find a way to maximize the potential of this motor.
 What do you know about torque?
 How can you find the torque that the motor exerts on a gear?
Make sure to write down all your calculations. You will need these for your presentation.
b) Now that you have an idea of what the motor is capable of, you can start planning your car.
Build your car so you know the car’s mass. This will affect the amount your wheels will need
to push your car and therefore how much power you need from your motor.
c) Now based on what you know about torque, what combination of gears do you think will
maximize speed and make sure not to sacrifice weight capacity.
d) Once your sketch has been approved, buy the items you need and begin building your
coaster. Note any changes to design you need to make in the Design Process handout. Make
sure to note your reasoning for your presentation.
e) After coming up with your design, build your cart and test it out. Do a few time trials to
make sure your velocity is at full capacity.
f) Discuss how come your original design didn’t work the way you’d planned. What
assumptions did you make at first that turned out to be untrue.
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Based on your calculations, did your car work?
Why do you think it didn’t work?
How do you need to redesign it to make it better?
Step
1) Problem: How
torque will affect
your car.
2) Research/Possible
Soln’s: Things you
will need to achieve
your goal (car
properties, gear
properties, wheel
properties, etc.)
3) Best Possible Soln:
Sketch Final design
features (Gear ratio
and sizes).
4) Soln. design
features and
calculations
Design Process Handout
Notes
5) Construct, test,
and evaluate:
Begin construction
of coaster. Note any
changes you make.
What assumptions
are not holding?
6) Communicate
Solution: What
changes did you
have to make.
7) Redesign: Draw
your final product.
What is your final
gear ratio?
Teacher Notes:
This is an exercise in applying the knowledge the students know to a real life situation. The
concept of torque is extremely complicated, but the purpose of the exercise is not really content based,
it is procedure and presentation. They need to be able to justify their reasoning to the best of their
ability and go through the design process. If their numbers aren’t perfect, it is not really the end of the
world. If they can be convincing of their process and reasoning and show proof that their car works
based on time trials and calculations, then the goals of the activity were met.
8. Time Table(2 Day lab or 1 day extended period)
Clock reading
during the lesson
0 - 5 min
“Title of the
activity”
Homework quiz,
receive feedback
Students Doing
Teacher Doing
Writing
Checking up equipment for
the first activity
Clock reading
during the lesson
5-10 min
“Title of the
activity”
Introduction,
statement of rules
and materials
Initial calculations
and preliminary
designs.
Students Doing
40-70 min (0-30 min
if continuing on
another day)
Build car, time trials,
assemble data for
presentations
Constructing car,
adjusting for errors in
design, reasoning
70 – 85 min (30-45
min next day)
Presentations
Students present final
design and give
reasoning “why their
car is the best”
10-40 min
Teacher Doing
Listening taking notes, Addressing class, showing
Getting into groups.
material
Working in groups.
Discussing designs,
calculating necessary
values, drawing initial
design.
Assisting students when
necessary. Helping students
get past design trouble by
asking probing questions
(see possible student
difficulties section)
Helping students get past
hurdles and difficulties in
design. Probing for
assumptions.
Watching presentations.
Making sure students reach
key points.
Giving students homework
assignment.
9. Formative Assessments:
Content Goals:
 Students can correctly reason force required to move car and find the torque necessary to
spin wheels to move car.
 Mention of sources of experimental uncertainty
Process Goals:
 Proper presentation of information in Design Process Handout.
 Answering homework question about engineering design process.
 Effective final presentation
Epistemological Goals:
 Students’ ability to accurately and effectively analyze assumptions and explain how they
affected the final result.
 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.
Metacognitive Goals:
 Ability to answer homework question on contribution to the team and design process.
 Effective final presentation
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) How accurate were your predictions of the amount of torque you needed to push the
car? What changes did you have to make?
2) What difficulties did you have in the engineering and design process ? (List at least one)
How did you overcome these difficulties?
Using your group’s data, create a presentation in power point that describes your design
process. Include all the proof you need to justify your reasoning (time trials, graphs,
calculations) with the purpose of convincing the engineering firm that your design is the
most efficient in terms of weight capacity and speed. Write a script to go with your
presentation that would be EXACTLY what you would say while giving it. This is a crucial
part of the design process that engineers must worry about (or rather, marketing
engineers) when trying to sell a design or product.