NASCAR Racing: restrictor plate rules, bobby allison, restrictor plates

Question
My son and I would like to know about the rules and requlations of the restrictor plates.  Are restrictor plates required for all the races?  My son says that Nascar requires restrictor plates for all races? I need your help for the answer.

Answer
The restrictor plates are currently used only at Daytona and Talledega but I believe they could become required at Atlanta soon if the cars keep gaining in speed.
The plates came about due to the cars getting too fast and they began having trouble keeping them on the ground. When Bobby Allison's car nearly soared into the grandstands during a race NASCAR finally decided that they needed to slow the cars at that track and all of the tracks where they running 200+ MPH.
Essentially, the restrictor plate restricts the flow of air to the carburetor. Gas needs an air mixture to burn, the more air the hotter it burns....meaning more speed. Cut down on the air, cut down on the speed. We'll see what the Cars of Tomorrow do speed wise at those tracks and maybe the restrictor plates can be done away with.