
Pondering The Existance?
No known species of reindeer can fly. However, there are hundreds of thousands, even millions of species of living organisms yet to be classified. While most of these are insects and germs, this does not COMPLETELY rule out flying reindeer which only Santa has ever seen.
There are 2 billion children (persons under 18) in the world. Since Santa doesn't (appear) to handle the Muslim, Hindu, Jewish & Buddhist children, that reduces the workload to 15% of the total  378 million according to Population Reference Bureau. At an average (census) rate of 3.5 children per household, that's 91.8 million homes. One presumes there's at least one good child in each.
Santa has 31 hours of Christmas to work with. This is due to the different time zones and the rotation of the earth, assuming he travels east to west (which seems logical). This works out to 822.6 visits/second.
This is to say that for each Christian household with good children, Santa has .001 seconds to park, hop out of the sleigh, jump down the chimney, fill the stockings, distribute the remaining presents under the tree, eat whatever snacks have been left, get back up the chimney, get back into the sleigh and move on to the next house.
Assuming that each of these 91.8 million stops are evenly distributed around the earth (which of course, we know to be false but for the purposes of our calculations we will accept), we are now talking about .78 miles/household, a total trip of 75.5 million miles; not counting stops to do what most of us must do at least once ever 31 hours, plus feeding etc.
So Santa's sleigh must be moving at 650 miles/second, 3,000 times the speed of sound. For purposes of comparison, the fastest manmade vehicle on the earth, the Ulysses space probe, moves at a poky 27.4 miles per second. A conventional reindeer can run, TOPS, 15 miles/hour.
The payload on the sleigh adds another interesting element. Assuming that each child gets nothing more than a mediumsize Lego set (2 lb.); the sleigh is carrying 321,300 tons, not counting Santa, who is invariably described as overweight. On land, conventional reindeer can pull no more than 300 lbs. Even granting that "flying reindeer" (see above) could pull 10 TIMES the normal amount, we cannot do the job with 8, or even 9 reindeer. We need 214,200. This increases the payload  not counting the weight of the sleigh to 353,430 tons. This is four times the weight of the oceanliner Queen Elizabeth!!!
353,00 tons traveling at 650 miles/second creates enormous air resistance. This will heat the reindeer up in the same fashion as a spacecraft reentering the earth's atmosphere. The lead pair of reindeer will absorb 14.3 QUINTILLION joules of energy!!! Per second!!! Each!!! In short, they will burst into flame almost instantaneously, exposing the reindeer behind them, and creating deafening sonic booms in their wake. The entire reindeer team will be vaporized within .00426th of a second. Meanwhile, Santa will be subjected to centrifugal forces 17,500.06 times greater than gravity, A 250 lb Santa (seems ludicrously slim) would be pinned to the back of this sleigh by 4,315,015 lbs. of force.
Therefore, if Santa ever DID deliver presents on Christmas Eve ... he's dead now.
Merry Christmas! 
