Fat man and the chimney

Ever wonder how Santa succeeds in dropping down a chimney and goes back up? The 1960's made a lot to do about pressing the side of his nose and "up he went". Nevertheless, this article offers some insight into the issue...maybe an answer? Hope there is no roaring fire.

The physics of Santa and the chimney: playful insights into a Christmas "mystery".

'Twas the night before Christmas and all through the house, not a creature was stirring, not even a mouse...

So begins the familiar 19th century poem about Santa's visit to a household where…

...the children were nestled all snug in their beds
while visions of sugar plums danced in their heads.

For children and adults alike, this classic story invokes the magic of the Santa Claus legend. This holiday season, a Harvard University professor invites us to imagine one aspect of the story as a mystery waiting to be solved by the laws of physics.

The mystery is how Santa gets up and down each chimney. According to the fable, Santa parks his sleigh at every house, goes down the chimney, and delivers presents under the Christmas tree for the good boys and girls of the house. According to the poem-a definitive source for Santa facts-the trip down the chimney is described as something of a free-fall:

...Down the chimney St. Nicholas came with a bound...

"If the typical household chimney is 30 feet tall, simply dropping down the chimney would be dangerous," points out Dudley Herschbach, a Harvard professor who finds this poem a fun way of illustrating science ideas in everyday terms. More than 350 Yuletides ago, Herschbach tells us, Italian scientist Galileo Galilei examined the motion of bodies falling under the constant acceleration of gravity. From Galileo's results, Herschbach says, one can calculate that in free-fall, Santa's descent would take about 1.4 seconds. "He'd hit the hearth at about 30 miles per hour," says Herschbach.

"So we can plausibly assume that Santa probably slides down a rope tethered to his sleigh on the rooftop," Herschbach concludes.

From the poem, we know that Santa is "chubby and plump," with a "little round belly that shook when he laughed, like a bowlful of jelly."

This gives Herschbach another clue on how Santa moderates his fall. "No doubt, by bumping his tummy on the bricks during descent he would further brake his downward plunge, while rappelling down his tether like a mountain climber," he says.

Going back up the chimney offers a much more challenging physics problem, says Herschbach. Santa could just climb, hauling himself hand over hand with his rope. But for such a chubby fellow that would be slow and strenuous, and much too demanding in view of his incredibly busy schedule. Even if Santa could leap like Michael Jordan, a quick jump up the chimney is also not feasible. With no room for a running approach, the jump would have to be from a standing start and the world record for a vertical high jump is only a few feet.

"To exceed that, and reach 30 feet, Santa would have to have means to blast off like a human rocket," Herschbach says.

Herschbach's simple calculations show that, in order to exit in a second or so, he would have to be subjected to uncomfortably strong forces. "Santa would emerge not merely tattered but fractured," says Herschbach.

Surely "laying his finger aside of his nose" is a telling clue, says Herschbach.

Santa's ascension can be understood through an intricate chain of events, according to Herschbach. "We can infer that in his cap he has a little electrical device, of a kind that would have delighted electricity pioneer Benjamin Franklin," he says. "The device evidently must be triggered by his finger, perhaps by interrupting a faint light beam near his glowing cheek. That would generate a photoelectric signal, by means elucidated in 1905 by Albert Einstein."

"The device could then send a radio signal to activate a winch on the sleigh, thereby winding up Santa's tether and enabling him effortlessly in the air."