The Junk Car Derby
The Basic Idea…
• You need to get a small car made from
junk (no pinewood derby cars!) down a
ramp in the shortest amount of time.
• You want to design your car so that it will
cross the finish line before other cars do.
• There are rules and specifications you will
need to follow to have a ramp-legal car.
¿Preguntas?
1. How do I get the car to the finish line?
•
If the wheels roll, gravity will do all the work.
2. How do I get my car to cross the finish
line first?
•
•
Propellants cannot be used.
Use the principles of physics!!!
3. What rules do I need to follow?
•
You will receive a handout with the rules
Let’s Explore the Physics
Conservation of Energy: The Basics
• The Law of Conservation of Energy:
Ei = Ef
• What types of energy do we have to start
with? To end with?
– Start: Potential
– End: Kinetic
• If energy is conserved, why don’t all cars
finish at the same time?
Conservation of Energy: Friction
• Mechanical Energy (Potential and Kinetic) is lost
to heat, sound, and light when there is friction.
Ei = Ef
becomes
Ui = Kf + Wfriction
• Friction Occurs in 3 places for our cars:
– Between the wheels and the ramp (this is negated if
the wheels roll)
– Between axels and the car body
– Between the car and the air (Air Resistance)
Conservation of Energy:
Decreasing Friction
• Formula 1 cars are shaped as they are for
a reason.
– Do some research on it and make an
awesomely, aerodynamic design.
– Make sure your design is possible with your
materials and resources.
• Lubricating your wheels can cut down on
internal friction. Make sure to follow the
rules for lubrication.
Conservation of Energy:
Rotational Kinetic Energy
• There is another type of Kinetic Energy
called Rotational Kinetic Energy.
– You need to “spend” potential energy to get
your wheels to roll.
– The more energy it takes to make your
wheels spin, the less Linear Kinetic Energy
your car will have.
• How can you decrease the RKE?
Conservation of Energy:
Decreasing RKE
• Is it easier to roll a heavy object or a light object?
– Lighter wheels!
• What shapes roll the fastest?
– Click HERE to watch the video
– The closer the mass is to the center, the easier it is to
roll an object
– Research “Moment of Inertia” to find out more and to
figure out how to create the fastest wheel
Conservation of Energy:
Conclusion
• Here is our Conservation of Energy equation:
Ui = Kf + RKE + Wfriction
• Goal: Maximum Speed (Kinetic Energy)
– Want high Gravitational Potential Energy
– Want low Rotational Kinetic Energy
– Want low Work due to friction
• Cars that best apply these physical laws to their
car design will win.
The Track
• Created by Clear Falls Engineering Students!
• Cars ride down guide rails for the lanes
• Example Heat 1, Example Heat 2
The Rules: Making the Car
• Follows the specifications on your rules sheet.
• You CANNOT use a Pinewood Derby Kit.
– You cannot use any object that was originally
manufactured to be a car.
– You cannot use any object that was originally
manufactured to be wheels for the wheels.
– You cannot use solid wood for the base of your car
(ex: no lumber, scrap wood, wooden doorstops, etc.)
• This is an individual project. Every student will
need to make a car for themselves!
The Rules: Car Specs
•
•
•
•
Car must be less than 142 grams (5.0 oz)
Car must be less than 7 inches long
Car must be less than 3 inches wide
Car must have 1 ¾ inch clearance
between wheels
• Clearance below car must be between ½”
and 1”
• No springs allowed
The Rules: Car Specs Clarification
Front View—Not to Scale
• Green Arrow: Maximum width (Includes both car body and both
wheel widths) - must be less than 3”
• Red Arrow: Clearance between insides of wheels- must be at least
1 ¾” apart
• Blue Arrow: Clearance below car (vertical height from bottom of
wheels to car body or axle) - must be between ½” and 1” high all the
way between the wheels.
The Rules: Car Specs II
• Car must be free wheeling; no propulsion
devices such as CO2, fans, etc.
• No loose materials; car must stay intact
• Only dry lubricants are allowed (ex:
graphite, powdered teflon, etc.)
• No lubrication after car has entered the
classroom; no lubrication between races
• Only one car may be entered per student
The Rules: Racing
• Cars will race in heats of 4 cars.
• Cars will race down the Clear Falls High
School Pinewood Derby Track.
• 1st and 2nd place cars advance to the next
round; Cars not meeting specifications
cannot advance.
• Car must be present on race day to earn
advancement points.
Grading
•
•
This project counts as a MAJOR GRADE, the
same as a test.
There are 3 parts to the Grade:
1. Proposal (25 points)
2. Car Build (50 points)
3. Car Performance (25 points)
•
•
For more information, look at your project and
scoring sheet.
Extra credit points (5 Points) can be won for:
Class Racing Champion, Best Looking Car
and Most Creative Car in each class period.
Time Line
• Proposals will be completed in class
tomorrow, Friday, November 21st.
• Cars must be completed and ready to race
on Monday, December 15th.
• Races will take place on Monday,
December 15th. Cars will be massed and
their dimensions will be checked at the
beginning of the class period.
Time Line II
• Get your car made early. You can always
check the specs (mass and dimensions) of
your car with your teacher before race day
to make sure your car is legal.
• This PowerPoint, the rules sheet, and the
project and score sheet are all available
on blackboard for you to reference.
GOOD LUCK!
“When the race starts, roll really, really fast”