For those of you who believe in Santa Clause... I have good reason to not.
There are approximately two billion children (persons under 18) in the world. However, since Santa does not visit children of Muslim, Hindu, Jewish or Buddhist religions, this reduces the workload for Christmas night to 15% of the total, or 378 million (according to the population reference bureau). At an average (census) rate of 3.5 children per household (what happened to the other half?!), that comes to 108 million homes, presuming there is at least one good child in each.
Santa has about 31 hours of Christmas to work with, thanks to the different times zones and the rotation of the earth, assuming east to west (which seems logical). This works out to 967.7 visits per second. This is to say that for each Christmas household with a good child, Santa has around 1/1000th of a second to park the sleigh, hop out, jump down the chimney, fill the stocking, distribute the remaining presents under the tree, eat whatever snack have been left for him, get back up the chimney, jump into the sleigh and get on to the next house.
Assuming that each of these 108 million stops is evenly distributed around the earth (which, of course, we know to be false, but will accept the purposes of our calculations), we are now talking about 0.78 miles per household; a total trip of 75.5 million miles, not counting stops to do what most of us have to do at least once in any 31 hour period.
This means Santa's sleigh is moving at 650 miles per second--3,000 times the speed of sound. For purpose of comparison, the fastest man made vehicle, the Ulysses space probe, moves at a poky 27.4 miles per second, and a conventional reindeer can run (at best) 15 miles per hour.
The payload of the sleigh adds another interesting element. Assuming that each child gets nothing more than a medium sized LEGO set (two pounds), the sleigh is carrying over 500 thousand tons, not counting Santa himself, who is invariably described as "portly." On land, a conventional reindeer can pull no more than 300 pounds. Even granting that the "flying" reindeer can pull 10 times the normal amount, the job can't be done with eight or even nine of them---Santa would need 360,000 of them. This increases the payload, not counting the weight of the sleigh, another 5,400 tons, or roughly seven times the weight of the Queen Elizabeth (the ship, not the monarch).
600,000 tons traveling at 650 miles per second creates enormous air resistance-this would heat up the reindeer in the same fashion as an aircraft re-entering the earth's atmosphere. The lead pair of reindeer would adsorb 14.3 quintillion joules of energy per second. Each. In short, they would burst into flames almost instantaneously, exposing the reindeer behind them and creating deafening sonic booms in their wake. The entire reindeer team would be vaporized within 4.26 thousandths of a second, or right about the time Santa reached the fifth house on his trip.
Not that is matters, however, since Santa, as a result of accelerating from a dead stop to 650 miles per second in .001 seconds, would be subjected to acceleration forces of 17,000 g's. A 250 pound Santa (which seems ludicrously slim) would be pinned to the back of the sleigh by 4,315,015 pounds of forcem instantly crushing his bones and organs and reducing him to a quivering blob of pink goo. Therefore...
If Santa Clause did exist...
He's dead now.
Merry Christmas little boys and girls.