# Bits of Books - Books by Title

## The Physics of Christmas

The Physics of Christmas: From the Aerodynamics of Reindeer to the Thermodynamics of Turkey

Roger Highfield

Roger Highfield, the departing editor of New Scientist who is about to join the staff of the Science Museum in London. In his popular book “The Physics of Christmas: From the Aerodynamics of Reindeer to the Thermodynamics of Turkey”, Dr Highfield allocates gifts to every child on the planet under 18 years of age—of which there are 2.1 billion, according to the United Nations Children’s Fund.

Assuming there are 2.5 children per household, Santa has therefore to make over 840m stops on Christmas Eve. If the homes were spread equally across the Earth’s landmass of 60m square miles, the distance between households would be 0.26 miles. Every Christmas Eve, Santa would therefore have to travel 220m miles.

“Fortunately, Santa has more than 24 hours to deliver the presents,” Dr Highfield points out. From the moment on the planet where the clocks are the first to strike midnight on December 24th, Santa can start popping down chimneys. But instead of hovering over a longitude waiting for the Earth’s rotation to bring homes to him, Santa can do better by travelling backward against the direction of Earth's rotation, notes the author. “That way, he can deliver presents for almost another 24 hours.”

With roughly 48 hours to do the job, Santa has a little over 0.2 milliseconds to scamper between households. To do so, his sleigh needs to average 1,300 miles per second. In aerodynamic terms, that represents a speed of more than Mach 6,000—well beyond any aerospace technology in existence today.

The escape velocity needed by a spacecraft to overcome the tug of Earth’s gravity is around seven miles per second—ie, Mach 34. However, 1,300 miles per second is comfortably below the speed of light—186,000 miles per second. So, Santa should not have to worry about the effects of relativity, Dr Highfield notes.

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