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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 379 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 at least one good child in each.

-Santa has about 31 hours of Christmas work with, thanks to the different time zones and the rotation of the Earth, assuming east to the 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 what ever snack that have been left for him, get back up the chimney, jump 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--3, 000 times the speed of sound. For purpose of comparison, the fastest man made vehicle, the Ulysses space probe, moves at a pokey 27.4 miles per second, and a conventional reindeer can run (at best) 15-20 miles per hour.

The payload of the sleigh adds another interesting element. Assuming that each child gets nothing more than medium sized LEGO set (2 pounds) the sleigh is carrying over 500,000 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 reindeer. 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 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 creating deafening sonic booms in their wake. The entire reindeer team would be vaporized in 4.26 thousands of a second, or right about the time that Santa reaches the 5th house on his trip.

Not that it matters, however, since Santa, as a result of accelerating from a dead stop to 650 mph in 0.001 seconds, would be a subject to acceleration forces of 17,000 Gs. A 250-pound Santa (which seems very slim considering 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.

Hmmm--so does Santa really exist..

Happy Holidays!