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 (except maybe in Japan)
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, 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 time 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 Christian 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 snacks have been left for
him to get back up the chimney into the sleigh and get onto 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 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 stops or breaks. This
means Santa's sleigh is moving at 650 miles per second or 3,000
times the speed of sound. For purposes 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. 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 54,000 tons, or roughly seven times
the weight of the Queen Elizabeth (the ship, not the monarch).

A mass of nearly 600,000 tons traveling at 650 miles per second
creates enormous air resistance this would heat up the reindeer
in the same fashion as a spacecraft 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 426 thousandths of a second, or right about the time Santa reached
the fifth house on his trip.

Not that it matters, however, since Santa, as a result of
accelerating from a dead stop to 650 m..p.s. in .001 seconds,
would be subjected to acceleration forces of 17,000 g's. A 250
pound Santa (which seems ludicrous considering all the high
calorie snacks he must have consumed over the years) would be
pinned to the back of the sleigh by 4,315,015 pounds of force,
instantly crushing his bones and organs and reducing him to a
quivering blob of pink goo. Therefore, if Santa did exist, he's
dead now.

Merry Christmas