Pinewood Derby Physics Race Group of Cars

Above is the screen you will see when you click on the [Race Group of Cars] tab. The track parameters have been changed so that we are racing on the longer inclined plane track at the National PWD race in Irving, TX, held on May 26, 2005.

Of all the cars that have been created by the user, the user can put a check mark by the ones that will be raced and compared for time only. The fastest car is the Perfect Car with the center of mass (CM) located at its imaginary rear wheels 7.38 cm behind the car center. The Perfect Car has zero entered for the coefficient of wheel/axle friction, for the drag coefficients of the body and wheels, and for the moment of inertia of the wheels. Move the CM of the Perfect Car to the center of the car at the neutral zero position, and the car won't have quite as much gravitational potential energy to use and will therefore turn in a somewhat slower time. Note the JNTS car, after which the Brett Bullet was designed, barely beats the Brett Bullet with MU = 0.06, probably because the JNTS was running wheels with a smaller wheel moment of inertia (called I). The Brett Bullet parameters are located here. The actual average of 4 times for the Brett Bullet in Irving was 4.039 seconds, close to the individual predicted time of 4.0479 seconds. Although nice to see, the absolute agreement with a real track race is not important. The relative differences in times between cars and finish order will hold for almost any similarly ramped track regardless of track height, length, and other dimensions.

A new feature has been added for VR-VII. The new Race Group of Cars screen is shown above, if you select only 2 cars, a new tab appears called [Graphic 2-Car Race]. You can still race these two here just for time, but the new tab takes you to a new screen which allows you to actually race and compare these two cars from start to finish on the chosen track. See Graphic 2-Car Race and Lecture 24 for details.