Santa Claus: An Engineer's Perspective
I. There are approximately 2 billion children (persons under 18) in the world. However, since Santa does not visit children of Muslim, Hindu, Jewish, Jehovah's Witnesses, or Buddist religions, this reduces the workload on 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, that comes to 108 million homes, presuming that there is at least one good child in each.
II. Santa has about 31 hours of Christmas to work with, thanks to the different time zones and rotation of the earth, assuming he travels east to west (which seems logical). This works out to 967.7 visits per second. This is to say that for each Christian household with at least one good child, Santa has around 1/1000th of a second to park the sleigh, jump out, go down the chimney, fill the stockings, distribute the remaining presents under the tree, eat whatever snacks have been left for him, get back up the chimney, jump in the sleigh, and move on to the next house. (That's why it's really pointless to stay up and wait for him....)
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 for 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 bathroom breaks. This means that Santa's sleigh is moving at 650 miles per second, 3000 times the speed of sound. For the purposes of comparison, the fastest man-made vehicle, the Ulysses space probe, moves at a pokey 75.4 miles per second, and a conventional reindeer can run (at best) 15 miles per hour.
III. The payload of the sleigh adds another interesting element. Assuming that each child has nothing more than a medium-sized Lego set (two pounds), the sleigh is carrying over 500 thousand tons, not counting Santa himself. On land, a conventional reindeer can pull nothing more than 300 pounds. Even granted that "flying" reindeer could pull ten times the normal amount, the job can't be done with eight or nine of them; Santa would need 360,000 of them. This increases the payload, not counting the sleigh itself, another 54,000 tons, or roughly seven times the weight of the Queen Elizibeth (the ship, not the monarch).
IV. 600,000 tons traveling at 650 miles per second creates enormous air resistance; this would heat up the reindeer in the same fasion as a spacecraft re-entering the earth's atmosphere. The lead pair of reindeer would absorb 14.3 quintillion joules of energy per second each. In short, they would burst into flames almost instantaneously, exposing the reindeer behind them and causing deafening sonic booms in their wake. The entire reindeer team would be vaporized within 4.2 thousandths of a second, or right about the time Santa reaches the fifth house on his trip. Not that it 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 centrifugal forces of 17,500 G's. A 250 pound Santa (which seem ludicrously slim) would be pinned to the back of the sleigh by 4,315,015 pound of force, instantly crushing his bones and organs and reducing him to a quivering blob of pink goo.
V. Therefore, if Santa did exist, he's dead now.