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• Balancing a pencil or any other tough, heavy object on its tip,

• is quite a precarious task.

• It is easy to see why tough heavy object are unstable.

• They justwanna fall down.

• Any little nudge, will put it off balance,

• with gravity, happy to pull its center of mass even more off balance

• And the more off balance, it is the more gravity pulls in too!

• Physicist calls this kind of tipping an...Inverted Pendulum.

• Because its kind of, likean upside-down pendulum.

• And careful mathematical analysis of Inverted Pendulums...will tell you the obvious,

• theyre reallyunstable.

• In fact, this equation predicts that

• if a perfectly balanced pencil with a perfectly-sharped tip,

• will do get nudge, off balance, by just one ten thousandth of the width of an atom.

• It would take only three seconds, to fall over...

• There are indeed acrobats, who can balance poles, with other acrobats on top.

• And the robots, they can balance and, catch and throw, upright sticks!

• And the people who make... seemingly impossible, artistic, rock stacks.

• But in all these cases,

• keeping the objects balance, either requires an active stabilization effort,

• Or else, carefully taking advantage of the fact that

• the balancing point...isn't actually...a point!

• So, the question is this:

• Can you balance a pencil sharpened to a perfect, single, atom-wide tip, on its tip?

• Without active stabilization?

• Well, to start, you better get rid of the air bumping in besides the pencil.

• Since the kinetic energy of a typical oxygen molecule,

• is enough to destabilize the pencil.

• Remember, if the pencil gets off center by even ten thousandth of the width of an atom,

• it would fall down in, under three seconds.

• And you better cool the pencil and table down as close to absolute zero, as you can...

• since the thermal jiggling of their atoms when they're hotter, are similarly jiggle the pencil off balance.

• But even then, matter add very small scales has spread out wape like nature

• which means that you cannot have both pencil perfectly upright,

• and not moving at the same time.

• And while this "quantum effect" is never a real life inhibitor of the precarious pencil balancing?

• It means, you never even could succeed...

• However, it is still fun to see, how long you can keep a pencil balanced on your fingertip.

• The shorter the pencil, the harder it is.

• My best time for a standard nineteen centimeter pencil

• was one point three seconds.

• Do you think you can beat that?

• This minute physics video is brought to you by audible.com

• one of the leading providers online, audio books, and all types of media,

• either fiction, non-fiction, and periodicals..

• I'd like to recommend "The Tipping Point" by Malcolm Gladwell this week.

• It is a book about exponential increases and spreads of trends,

• social trends, academic, that sort of thing,

• and...the mathematics of, the mathematics of... balancing an object, on its...tip,

• so...anyway,"The Tipping Point", by Malcolm Gladwell,

• audible.com, supports minute physics.

• Without them, we won't be able to do... what we do!

• So, thank you to audible and

• have an audible.com/minutephysics to get your free audio book.

Balancing a pencil or any other tough, heavy object on its tip,

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# How Long Can You Balance a Pencil?

• 1994 94
Go Tutor posted on 2014/09/20
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