Now, with Christmas fast approaching, and children all over the world eagerly awaiting Santa's arrival, just how does the man in red do it? Firstly, this exercise has been repeated before and I make no apologies for redoing this subject. Now, onto the science. It's estimated there are 2 billion children in the world under 18 years of age. Santa is primarily a figure in the Christian religion so that leaves around 380 million kids, around 15% of the total, according to the Population reference Bureau. At an average 3 ½ kids per household that's about 92 million homes to visit. We will also assume no children are on the naughty list, a big assumption in my experience.
Luckily, thanks to time-zones and the rotation of the Earth, Santa has 31 hours to do his rounds. If he follows the night and goes East to West that works out at about 825 houses to visit per second. If we assume all the houses are evenly distributed, that gives Santa around one millisecond (one thousandth of a second) for each house. We can now estimate his total journey on Christmas night to be around 75 million miles, phew! To cover that distance Santa, his sleigh and the poor old reindeer will have to travel at around Mach 3000, or about 650 miles per second.
Now, the sleigh has to be filled with presents. Assuming each child gets a modest present, weighing about a kilo, that give a total weight of just under 400,000 metric tons. In reality it's estimated that reindeer can each pull a load of around 150 kilos, so he would actually need just under 3 million reindeer. Now, all that weight travelling at that incredible speed would create a massive amount of air resistance. One estimate is that the leading pair of reindeer would be absorbing around 30x10^18 Joules of energy per second and be subject to forces of around 18,000 g. It's no wonder the big guy and his flock need the rest of the year off!
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