Rubber Band Car by Shawn Beightol Michael Krop

Rubber Band Car* by Shawn Beightol, Michael Krop Sr. High School, Miami, FL September 08, 2006 *Adapted from Brad Nunn’s (Purdue University) Feb 25, 2006 Presentation

The Mantra: n n n Smaller! Lighter! Farther! Say it again! Do the Math…

Today’s Activities n n n Typical rubber band cars Propeller based designs Review competition rules Component design Build!

Typical Rubber Band Cars

Typical Rubber Band Cars

Typical Rubber Band Cars

Typical Rubber Band Cars

Dixie Roller

Propeller Rubber Band Kit

Propeller Rubber Band Cars

Propeller Rubber Band Kit

Review Rules n Refer to Go Cart Competition Construction and Operating Rules

Review Scoring F = 1 D 2 * W L • Consider tradeoffs - (D+L squared) • Smaller! • Lighter! • Farther!

Terminology n n n Potential to kinetic energy transfer Torque Acceleration Speed Momentum Friction

Desired Outcomes n A small car that travels 2500 cm and doesn’t weigh much • Smaller! • Lighter! • Farther! n n A gradual transfer of energy that has just enough torque to establish motion A sustained transfer of energy that delivers sufficient momentum to cover the distance

Competitive Benchmarks • 2004 -5: • 2003 -4:

Score as a function of Length

Score as a function of Mass

Thoughts from analysis of competition data: n n n n Competition formula suggests F a 1/L 2 – this should be most significant Data supports this with a power function of 2. 5 Correlation is low! (0. 3) F a W –mass should be less a factor Data suggests in practice this is more significant with a power function of 2. 0 Correlation is almost twice as high (0. 5) Interpretation? Students assemble long vehicles from kits without thinking? Students who modify for mass acquire and apply design skills?

The Mantra: n n n Smaller! Lighter! Farther! Say it again! Do the Math…

Rubber Bands n All shapes and sizes n Experiment!

Component Design n Low inertia and light weight

Wheel and Axle Design n Minimize friction loss

Lubrication n n Graphite powder Silicone spray (WD-40 is not recommended)

Creative thinking n n What advantage is there to winding a rubber band compared to stretching it? Are there other ways to use a rubber band that is wound up?

Iterative Design n n n Prototype Measure and record performance Tweak the design (smaller, lighter, farther) Iterate Replicate Calculate Celebrate

Design optimization n n n Frictionless bearing Frictionless unwinding of the rubber band Thick or thin rubber band Length of the lever arm How many wheels Wheel materials for low inertia

The Mantra: n n n Smaller! Lighter! Farther! Say it again! Do the Math…

Most important n Have Fun!