Grandma Got Run Over By A Reindeer

Remember this Christmas song?

Grandma got run over by a reindeer
Walking home from our house Christmas eve
You can say there's no such thing as Santa
But as for me and Grandpa, we believe 

She'd been drinkin' too much egg nog
And we'd begged her not to go
But she'd left her medication
So she stumbled out the door into the snow 

When they found her Christmas mornin'
At the scene of the attack
There were hoof prints on her forehead
And incriminatin' Claus marks on her back

So I got to thinking. What would happen in a collision between a reindeer and an elderly woman.

While the song seems to imply that Grandma may have already been lying drunk in the snow and was then trampled by the reindeer, I’ll assume a more violent interaction. She was walking, and the reindeer, running down the road, hit her from behind.

Typical Diagram Drawn by a Physicist

The physics here involves the conservation of momentum. To simplify the problem, I’ll assume that the collision is like the one between billiard balls, what a physicist calls an elastic collision.

Momentum is the product of an object’s mass and its velocity.

A fundamental principle of the universe is that momentum is conserved; that is, this quantity of motion doesn’t change. It is mathematically expressed like this.

In collisions like ones with billiard balls, the total kinetic energy also is constant.

Let’s suppose this reindeer weighs 400 lbs. and was running at a speed of 45 mph. Let’s also suppose Grandma weighs 110 pounds and was walking at 4 mph.

With a bit of algebra we can find what happens to Grandma. It ain’t pretty. Grandma flies forward with a speed of almost 70 mph.

CREDIT: coolthings

Now about this family that let’s an old woman drink too much and then let’s her trudge all alone through the snow. 

Twas the Night Before What?

CREDIT: unknown

Isaac Newton, who in my not-so-humble-opinion may have been the smartest person to have lived, was born on the 25th of December 1642.*

In honor of his birth, I stole adapted the poem attributed to Clement Moore.  Here is

Twas the Night Before Newtonmas.

Twas the night before Newtonmas, when all through the house
Not a field was changing, not even a gauss.

The test tubes were stacked by the sink with care,

In hopes that Einstein soon would be there.

The faculty were huddled all smug in their wool threads,

While visions of bosons collided in their heads.

And the Dean at her desk, and I in my lab,

Had just collimated the particle beams at Fermilab.



When out on the quad there arose such a clatter,

I sprang from the lab to see what was the matter.

Away to the window I flew like a photon,

Tore open the shutters and spied an electron of Compton.



The radiation through the nearly ideal gas

Gave a Cerenkov blue hue to objects of mass.

When, what should appear in the department,

But a miniature CERN, and eight grad students.



With a little old professor, proclaiming "nein, nein, nein!",

I knew in a moment it must be Albert Einstein.

More rapid than eagles his coursers they came,

And he whistled, and shouted, and called them by name!"

Now Bethe! now, Boltzmann! now, Maxwell and Feynman!
On, Noether! On, Pauli! on, on de Sitter and Gell-Mann!

To the top of the chart! to the top of the graph!

Now graph away! Graph away! Graph away staff!"

He sprang to his office, and his team of academicians,

And away they all flew like the neutrons of a fission.

But I heard him exclaim, ‘ere he theorized out of sight,
"Happy Newtonmas to all, and to all a good-night!"



*In an amazing coincidence, Galileo Galilei died this same year on the 8th of January.

Santa Claus Science - Part 1

How does Santa do it?  Deliver all those presents to the children of the world.  Let's consider what his task entails.

There are 6.79 billion people in the world, 1.855 billion are children.  Sad as it may seem to some, but I don't think Santa visits all the good children of the Earth.  Santa only visits Christians.  Since Christians are 32% of the Earth's population, it seems reasonable to assume Santa has to visit 594 million youngsters under the age of 15.

Suppose each child gets one present, and that present has a mass of 1 kg.  (2.2 lb.s of weight for you non-SI people).  Santa gets to lug around 564,000 tonnes of toys.  Reindeer can pull up to twice its weight.  The jolly one then has to harness over 3 million reindeer to his sleigh. 

Speaking of the sleigh - let's assume each present fits in a cubic box 15 centimeters (6 inches) on a side.  With 594,000,000 presents to deliver, Santa is going to need a large sled.  He needs to haul 2 million cubic meters of presents.  Since the world's largest supertanker has a capacity of 670,000 cubic meters, the rotund one will need three of them and an additional 8 million reindeer.

11 million reindeer.   Imagine all that poop.