I want to find the car speed on my iPhone when driving so what should I use and how? Core Motion or Core Location? Is there any documentation or sample code?
Hey - You'll want core location for this.
There is a really good tutorial here - http://www.vellios.com/2010/08/16/core-location-gps-tutorial/ that I followed once. There is a whole series but this one shows you how to calculate the position and speed of your device. There is a sample project to download too. Hope this helps!