Velocity and Racecars
An activity from the Burroughs Wellcome Student Research Program The Science of Sports

Problem:

The object of racing is to go fast, however many factors act against the forward motion of a racecar. Forces such as air resistance and friction are just some of the factors that influence the speed of a race car. In this contest you will use the principles and techniques you have learned so far as you race a car down a ramp. How can you increase the velocity of a gravity propelled car?

Materials

Computer

ULI and MacMotion software
OR
LabPro and LoggerPro software

1.5 meter ramp
assorted masses
books to support ramp
toy car or cart
masking tape
other random materials

Procedure:

Set up a ramp on books as shown above. The high end of the ramp should be 45 cm from the floor. Place a large book 1m from the bottom end of the ramp. This book will stop your car after it comes off the ramp.

Tape a meter stick down the center of the ramp. The 0 cm mark should be at the very bottom of the ramp. In this position, the meter stick will serve as a guide rail for your car. Tape a card to the back of your car. Tape the Motion Detector upright at the top and center of the ramp and connect it to the ULI or LabPro.

ULI: Open the file EXP36.MXP from the Physical Science with Computers experiment files of Mac Motion. Open the calibration file EXP36.CLB. The vertical axis has velocity scaled from -0.5 to 3 m/s. The horizontal axis has time scaled from 0 to 3 seconds.

LabPro: Connect the LabPro and turn on the computer. Plug the motion detector into DigSonic1 of the LabPro. Once the computer is on, open the LoggerPro program. Under the Experiment menu select Show Sensors and choose the motion detector in the appropriate port. Under File choose Physical Science With computers and the file 36 Velocity.xmbl The vertical axis has velocity scaled from -0.5 to 3 m/s. The horizontal axis has time scaled from 0 to 3 seconds.

Exploring I:

Place your car on the ramp with its front at the 40 cm line. Click on the Start button and release the car after the Motion Detector starts clicking. Choose Statistics from the Analyze menu. Record the maximum velocity for 4 trials. Repeat the process at 60 cm and 80 cm distances. Calculate the average velocity for each trial. Graph Release Positioin versus Velocity.

Discussion I:

• Describe the shape of the curve on your graph.
  
• What happened to the velocity as you released the car from higher points?
  
• Describe two ways you could make the car go down the ramp faster without changing the height of the ramp or the release position.
  
• What slows the car? Be specific.

Exploring II: Race Day!

You may use your own car or temporarily modify a laboratory car supplied by your teacher. You are encouraged to make changes that will increase the speed of the car.

The car may only be powered by the pull of gravity. It may not otherwise be pulled, pushed or propelled. You are encouraged to experiment and practice before the contest.

During the contest, your car will get two runs down a ramp set up by your teacher. A Motion Detector will be used to measure velocity. The greater velocity of your two runs will count and the winning car is the one with the highest maximum velocity.

Discussion II:

Describe 3 specific things you did to increase the velocity of your car.