Physicists Explain This!

[Kuan]

http://www.youtube.com/watch?v=W1TMZASCR-I

[powerpig]

Easy although I'm not an expert. When placed on the cans, the motion created causes them to sync up. Something to do with perpetual motion.

[Botnst]

That's what I think, too PP.

The cans allow the mean of the pendulum energy to exactly balance at some harmonic, shifting it from periodic motion to linear motion.
Sum(T)=sum(2(pi)(L/G)^1/2) = - m/2 v^2

That term on the right side is negative to indicate equal and opposite. But there is still potential energy stuffed away in the instantaneous pendulum positions and so, the pendulums do not freeze in place. Instead, they continue their motion but reduced by the loss of kinetic periodic motion to kinetic linear.

Just when the pendulums thought it was safe to resume swinging, they hit another mean harmonic and again, get reduced.

Each time the harmonic is reached the KE is reduced. The pendulum most out-of-phase is most affected, it absorbs some of the KE transfered to the linear motion, which adjusts it's swing into phase with the mean phase of the other pendulums.

How's that?

B

[Dubyagee]

According to my book of magic, tiny invisible monkeys line them up.


They use setups like that in skyscrapers in Japan. They mount the water tank hanging from the ceiling of the top floor to counter earthquakes.

[Botnst]

Water towers? I didn't know that. Clever and makes a hell of a lot of sense.

Wonder what it does to vertical motion -- is the waterball spring-loaded?

[Medmech]

Originally Posted by Botnst

Water towers? I didn't know that. Clever and makes a hell of a lot of sense.

Wonder what it does to vertical motion -- is the waterball spring-loaded?

I'm looking for a source I saw a NOVA about earthquakes and Japanese skyscrapers about it, some even have hydraulic footings.

[Emmerich]

The water is just convenient. Most of the time a large mass is used to reduce sway in wind conditions, basically a big shock absorber. For earthquakes thev may have some sort of system in the foundation to prevent too much movement/damage. The water is easier because it can be pumped up, the large mass has to be moved up to the top in pieces and assembled, very difficult to do.

Originally Posted by Dubyagee

They use setups like that in skyscrapers in Japan. They mount the water tank hanging from the ceiling of the top floor to counter earthquakes.

[Dubyagee]

http://findarticles.com/p/articles/mi_kmtpi/is_200704/ai_n19005736

[Hatterasguy]

Its magic!

[Jim H]

When the metronomes are on the table, any back-and-forth force imbalances are resisted by the force from friction of table acting on the wood strip. Unless the motion/force is great enough, they do not move.

Now, by taking the wood off of the table and placing it on rollers (cans) there is a lot less friction to resist andy back-and-forth motion.

Unless acted on by an external force, the net sum of all of the back-and-forth of the metronomes, must be zero, so the wood strip moves in response to this net sum at every instant.

Since there is a small amount of friction on the rollers, the strip does not move exactly to the sum, and some energy is lost moment to moment. The energy loss causes the metronomes to change beat slightly, and this energy loss continues until they finally synchronize, eliminating any net force and further energy loss.

Without rolling friction of the cans, the wood strip would keep wobbling back and forth in response the instantaneous force differences, and the metronomes would not synchronize.

All in all, a very cool demonstration.

I hope this is right, and that it makes sense...

[MS Fowler]

Jim,
I think you and Bot agree.
WOW!

[Kuan]

Hmm I kinda get it. The moving board subtracts the difference between the two peaks? Sorta? Yeah cool.

[280SE Guy]

You will be assimilated.