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? How do I get the car to the finish line? If the wheels roll, gravity will do all the work. How do I get my car to cross the finish line first? Propellants cannot be used. Use the principles of physics!!! 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. 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) Ei = Ef becomes Ui = Kf + Wfriction

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: 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. Ui = Kf + RKE + Wfriction

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: Proposal (25 points) Car Build (50 points) 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.

“When the race starts, roll really, really fast” GOOD LUCK! “When the race starts, roll really, really fast”