How do you know the cars are moving? Moving with respect to what? How fast are they going?
![](http://bulldogbulletin.lhhosting.com/images/USA-09.gif)
We know that the cars are moving in reality because reality is superior to my fictitious model. In my fictitious model, the cars *appear* to be stationary.
In reality, the cars are traveling at 70 miles per hour, as stated in the initial pre-condition above in this thread. Check their speedometers!