• http://photon.iyte.edu.tr/PhysicsNet/Topics/Dynamics/Forces/FrictionalForce.html
• http://master.ph.utexas.edu/CTC/TMelching/modules/intro.html

Here are some links regarding the hardware and software:

• http://www.compumotor.com/ - Compumotor, maker of the computer-controlled motor
• http://www.compumotor.com/manuals/1020/CPlus.htm - Compumotor Plus^TM User Guide
• http://www.compumotor.com/support_samples.htm - Compumotor Support and Sample Files
• http://msdn.microsoft.com/vstudio - Microsoft Visual Studio Home Page
• http://msdn.microsoft.com/vbasic - Microsoft Visual Basic Home Page
• http://www.pasco.com - PASCO Homepage, maker of the photo gate and photo gate timer