I must disagree.

First, it's precession, not procession, paired with the "caster effect" and static friction. It's a self correcting system that only works when in forward motion.
This nonsense with counter rotating wheels countering the gyroscopic effect ignores the fact that only the forward rotating wheels are using friction to direct the path of the bicycle based on their angles. It's not JUST the gyroscopic effect, that only determines the resistance to angular change, it's friction directed by gyroscopic precession and the self correcting caster effect. Come on.

Nobody knows how we ride bikes?! (A different claim from we don't know why they can remain upright when ghost ridden) Nonsense, it's balance plain and simple. If you don't keep the center of gravity exactly above the contact points with the ground, you tilt. When the centrifugal force exceeds static friction of the tires you slide out or when gravity exceeds the opposing centrifugal force caused by turning, you fall. Try turning your bike but staying exactly upright, no lean. Now, when you heal, try leaning without turning, lock the wheel straight, you'll fall again. It's multiple forces in concert.

I think a decent physics teacher would wipe the floor with this. It ignores so much to make these "we just don't know" claims.

@newtboy ah finally see what you mean. And yes you are right a Coke can would be stable and it could rotate. It is no longer considered a spinning top I think, so that is why the contestants didn't make it that way but for sure it would work.

If the can rotates I think the torque (force due to rotation) is in the same direction as gravity. (Where in the normal spinning top case gravity pulls the cg off center and torque back on.) In the can case both would move the cg back to equilibrium, Ie on center. there would be no precession at all. Every time some small Bump would make the cg move of the center axis it would be pulled back instantly.

I think it would work, and that it would take away the challenge ;-)

Good question. I think that the entire device is unstable no matter what, its impossible to keep it straight no matter where the point of gravity as long as it needs to balance on a single tip. So zero speed would mean tip over in all cases unless you make a more stable tip (square) which would mean it cant spin very well which means you havent made a spinning top.

You can find more about the physics of the spinning top here:
http://hyperphysics.phy-astr.gsu.edu/hbase/top.html
and here:
http://physics.stackexchange.com/questions/271/why-dont-spinning-tops-fall-over

So what is the optimal distance of the center of gravity to the tip?

There are several things working at the same time. Most importantly is the energy. You need to store as much energy as possible so that the top can spin for as long as possible. When the top slows spinning the friction at the tip becomes larger (the precession becomes bigger) so it starts to lose more energy and slows the spinning even more. You store energy by adding weight with a center of mass that is further away from the tip. When the top then "falls" the center of gravity moves down and reduces potential energy. Due to energy conservation kinetic energy goes up meaning speed of precession or of spinning goes up and creates a force pushing the top back up.

Off course, more mass means more friction at the tip, so there is for sure an optimal here, most likely depending on mass, size and shape of spinning top, etc.

Last but not least, more rotation speed I assume also means more friction, so its a trade-off.

If you move the center of mass down below the tip, well, if you move it as far off as you would above, the energy you can save is about the same, but the entire thing would be harder to build and you would need to make sure the sides fit around the ground plateau. Also, when the precessions become bigger the sides will hit the plateau, meaning game over.

In the end you are better of keeping the center of gravity above the tip point.

There's also the fact his arm, wrist, and hand are rotating in a natural way instead of dead lifting without rotation. Grab a 40lb hand dumbbell and lift it straight up and then lift it up allowing your arm to rotate it however it feels.

You note when he dead lifts, he goes from palm-towards himself to palm-away, but with it spinning he rotates from palm towards to palm towards, but facing up during the main lift past his shoulders, rotating to palm away at the top.

The speeding up of precession just accelerates the rise initially not during.

Regarding precession, much of modern Western astrology does not make that correction, but Indian (Vedic) astrology certainly does. The correction is called ayanamsa in Sanskrit and is considered very important in casting Indian charts. Some Western astrologers also perform a correction, using a process that is actually closer to the way the ancient Greeks did it.

In more general astrological terms the difference is called tropical vs. siderial astrology.

Um, Bill Nye? Do you think that astrologers are really unaware of the precession of the equinoxes?

What do you think that whole "Age of Aquarius" thing was about?

As any basic introduction to astrology--heck, the Wikipedia entry on astrology--will tell you, there are two different ways of calculating the signs: tropical and sidereal. Under sidereal astrology, your sign is based on the actual constellation. Most people who think of themselves as a Sagitarrius really will be a Scorpio under sidereal astrology.

Tropical astrology, the most popular form of astrology in the West, is on the other hand based not on the positions of the constellations, but based on the position of the sun at the equinoxes and solstices. The signs are named after the constellations that were present in them back in the day, but it's not as if the equinoxes occur at different points in the year than they used to.

Whether or not you think astrology is bogus or not, it's probably a good idea to at least read the Wikipedia entry on a subject before you criticize it.

>> ^Boise_Lib:

I thought that I understood precession, but I learned something here.
Thanks, Skeeve.


Well I had it on mute so I didn't learn a damn thing...guess that makes me smarter than you.

I thought that I understood precession, but I learned something here.
Thanks, Skeeve.

As an artist and a painter, there is nothing new here that I didn't already know or understand.
I had hoped he would zoom in more and identify the bonding precess of the latex particles.

Different types of paints bond differently. (oil, water colours, latex, acrylic, gouache, egg)

Acrylic is quite different than most paints as once the medium evaporates and the pigment binds, it cannot be redissolved.Once the barrier between the pigment particles is removed, the pigments bond to one another to become a larger particle, on and on until the paint is dry and the particles form one large piece of solid plastic - never again to be separated.

Water Colours have no binders in them at all so once the water evaporates, the pigment just drys on the paper. Re-introducing water again will lift the pigment again as the process starts over. (minus pigment particles that get caught in the tooth of the paper.)

Oil paints stick together in linseed oil and are bonded by the linseed. It causes a strong bond but oil paint can be dissolved again using the right solvents. A varnish is used not to adhere (or fix) the pigment but to both hide linseed imperfections and to protect the paint surface from scratches.

Latex paint is a rubber (unlike plastic acrylics) and the process for the drying is different again. Anyone ever watch a foam rubber pour?

With all the differences, this video gives a rather slim and elementary vision of what is going on. It's more a document of evaporation more than anything as we watch the water dissipate and leave the pigment behind to stack on itself.

I would really like to have seen the actual pigments bonding with each other. I would also have liked to have seen different paints in comparison.

(..looking up perihillion, precession, & aphelion in the dictionary)..

I concur!!
>> ^jonny:
Right, SpaceDude - I fell into the trap of thinking in a hemisphere centric way. Perihelion will bring the southern hemisphere closer to the sun during the southern summer, but aphelion will put the northern hemisphere further away during its summer. I'm guessing it's just coincidence that perihelion and aphelion occur very close to the solstices. Precession of the earth's axis would change that over time, right?

Fair enough, longde. Their stated answers were wrong. I'd argue the editing helped that, but it's not really worth it. In any case, if this is grade school stuff, why would Harvard (or any college) professors be wasting their time teaching it to students. Wouldn't they assume their students have basic science knowledge? I think this falls under the "use it or lose it" principle. I studied geometry proofs in high school, but never really used it since. If someone walked up to me with a camera and asked me to give a proof for the equivalence of alternate interior angles, I'd probably be stumped too.

Right, SpaceDude - I fell into the trap of thinking in a hemisphere centric way. Perihelion will bring the southern hemisphere closer to the sun during the southern summer, but aphelion will put the northern hemisphere further away during its summer. I'm guessing it's just coincidence that perihelion and aphelion occur very close to the solstices. Precession of the earth's axis would change that over time, right?

What a happy coincidence. I was just thinking about the analemma the other day.>> ^rottenseed:

I find it rather awesome that the tilting cycle of the earth is so close to its cycle around the sun. Is this just a coincidence or is there a force that makes these 2 cycles so close in value?
I think you misunderstand what's going on there. The Earth's tilt doesn't change noticeably during a sidereal year. The precession cycle is about 26,000 years.
Opposite hemispheres are pointed toward the sun at each solstice because the tilt doesn't change.

>> ^shuac:

Turtles all the way down.

Dang. You beat me to it.

The crash reminded me of a rolling coin when it stops rolling and starts precessing. The extra 1:15 of running footage at the end was a real tease though -- why leave that in without including footage of the damage?

And I agree that the monowheel concept is totally impractical, but it sure looks cool!

http://www.thebikergene.com/custom-bikes/video-mclean-monowheel-inventor-nearly-killed-by-his-own-machine/

Despite the eye-grabbing headline, he was not seriously injured in the crash. The top comment on this site it dead-on though:

"How many times has this concept been tried, and failed? These guys (monowheel enthusiasts) always seem to have a good grasp of engineering, but damn little understanding of physics.

A single wheeled machine will never be able to accelerate as hard as a two wheeled machine, nor brake as hard (the only torque that acts to counteract the acceleration/braking forces is caused by gravity acting on the occupant and power system - if these are not sufficient, the rider begins to roll with the wheel, with all the resultant loss of control). Emergency braking is out of the question.

A single wheel can never turn as well a two wheeled vehicle - the one wheel is very stable, and resists leaning. Without any way to introduce a force that will force this big gyroscope to precess (which counter-steering does in a motorcycle), quick turns are impossible. Slight turns can be accomplished by shifting the weight of the occupant/engine to the side, or by the rider dragging his feet - not so safe, as we see in the video.

I fail to see what, if any, advantage this arrangement has that keeps bringing people back to it. Poor acceleration, poor braking, slow turns, and a need to drag your feet through intersections - now that I think of it, this would probably appeal to a lot of the cruiser crowd as is."

It must be said that the bike is very stable at high speeds -- it really wants to stay upright and go in a straight line, provided its wheels aren't out of kilter and the road surface is flat, level, and smooth (probably depends on a couple other things too). Gyroscopic precession, people. The weight of the motorcycle (~500 lbs., not counting the guy) also helps I should think. The hardest part was probably managing not to get blown off.