Billiard 2

[Athina Dollison]

Thisis an incredibly naive question so this may be closed. Nevertheless, I have been reading about the problem asking if every obtuse triangle admits a periodic billiard path, which has been open for a very long time. As someone who has not worked on this problem, I am wondering why what (on the surface) appears to be a "simple" problem is in fact so difficult to solve.

From the little I have read, it would appear that there has indeed been progress into the problem by the likes of Schwartz, Halbeisen et al., Vorobets et al., and more, however none have actually solved this problem. I find it curious that finding periodic billiard paths for acute triangles via the Fagnano billiard orbits is so natural and even simple, yet as soon as the same question is asked about right or obtuse triangles the ease in answering the question is vanquished.

Would anyone here be able to explain to me why this is (I know why Fagnano orbits do not exist in obtuse/right triangles), and how we happened upon methods such as unfoldings to be the best machinery in asking questions about this problem?

I am not sure why it is so hard. All I can really say is that, after a lot of experimentation, I can't really see any pattern to it. It might be hard in the same way that building the fountain of youth is hard: nobody has any idea what to do.

Sometimes I have described the problem as being akin to riding your bicycle to the North Pole. You know in advance that something is going to go bad for you, but it is hard to know what that will be exactly.

It seems that hexagonal paths are not possible and with higher order paths, even when some obtuse triangles are hit, each configuration will probably cover only a small patch of the space of obtuse triangles, much like pentagons already only partially cover the acute triangle space.

Brenda- I used to know a guy in Minneapolis/ St Paul who carved

bowling balls. His name is Alan Christian and he has The House of

Balls. He does a bunch of sculpture with found materials, but his

bowling ball carvings were amazing.

I visited the House of Balls several years ago, bought a piece. When

I went there, the place was littered with beer bottles, cups,

napkins, etc, from a party the night before, and Alan was hung over

but friendly.

I agree. Gripping the ball in the saw vise can be accomplished by

first sanding a flat on opposite (waste) sides of the ball. My

thought is that if the ball is nestled into drilled holes and clamped

down tight, there is a good chance that the force of the blade might

spin it out of position, especially since the lapidary saw uses an

oil coolant.

Some of the suggestions had some merit, or might have had, if we

knew what was wanted. For example, someone suggested sandwiching and

clamping the ball between two pieces of plywood which had round

holes into which the ball might nestle. I thought that was a pretty

good start. But how tightly would you have to clamp the wood

together to keep the ball from rotating under the influence of the

saw, whether the saw was used with reciprocating motion (like a hand

saw) or if it were some kind of circular saw? And if the ball did

turn, what would guarantee it would rotate without its axis shifting

and thus deviating from the intended plane of the saw cut? And if it

were held tightly enough, how soon would the pressure close the cut

against the sides of the saw?

It is probably no deep secret, but who has taken the trouble to find

out what kind of plastic billiard balls are made of? We know from

their intended use that they must be very hard material to withstand

repeated point impacts from others of their kind. But how would the

material behave under a drill or saw? Would it melt or create an

impossible gunk or unclearable chips? Abrasive cutters (diamond

wheels and the like) seem to get nowhere but into trouble with most

plastics. The little work i have done with drilling and cutting

(some) plastics tells me that drill bits and saws have to be shaped

much differently than for cutting in wood or metal or stone. Edges

have to be ground into quite surprising shapes - nothing I would

have guessed at without informed advice. Cutting speeds and pressure

also is different. Wrong shape or too much pressure and wild

chipping, melting, or fractures suddenly appear to spoil your day.

Over the years, a lot of different materials have been used to make

billiard balls, including ivory. During the first half of the

twentieth century or so one of the materials used was celluloid, the

same material used for making photographic film. Celluloid has the

potential to be extremely flammable, if not down-right explosive

under the right conditions, hence the urban myth that hitting one

billiard ball with another hard enough could cause an explosion (it

actually takes much more force and heat than that to cause a

reaction, a rifle shot or torch flame for instance). They are now

made using other compounds based mainly on silicates that are much

more stable. Unless the actual age (made after the forties or

fifties) and/or composition of the ball in question is known, I would

make sure that any cutting procedure used is cooled with some type of

water drip like that used in lapidary or masonry work. Just in case.

This has been a good and informative discussion. No problems, Marty.

I am getting the picture that the work is not what I have equipment

to accomplish. I may just cut by hacksaw. Nothing to lose, really. I

am mostly wanting the number with sufficient material around it to

use as a cab, and the extra to drill and somehow hang. Not sure yet.

I have looked at pics of many different pieces.

Mick, the ones I posted are from my CA X10 Library, I just typed in Pool Table, and they pop up. I did type in Rec and Rec Room and Games that Eric posted shows up. If you click on Billiards in that folder, there are several options that open up.

Thanks Bob it must be in a Library I don't have eg a grouped Room or something , I don't have it or any Rec Room Folder , I thought perhaps it had migrated forward from an old version, but couldn't tell from Eric's Pic what the exact name or type was....

We need to hear from Skip D the OP, who asked for a billiard table, not a pool table. Billiard tables have no pockets. One or more of those shown at the 3D Warehouse site are true billiards tables, but the great majority have pockets.

I've a friend who has an expensive billiard table and plays. Its slate top has electric heating elements to regulate its temperature to a tournament-level standard. He has a smartphone app to turn it on from wherever he is so it is ready to play when he gets there.

I too don't return any results when typing in Pool Table, Billiard, or anything else. Gene, I had no idea about Billiard, Pool Table or other characteristics of this game. I did find a result with the Chopsaw's suggestion of 3d Warehouse and was able to download something even though I don't use Sketchup, unfortunately the one I chose has some strange polyline solid adjacent to the item that I haven't been able to get rid of. Need to choose a different one I suppose.

Thanks Kbird! We are revamping this catalog and will be breaking it into some sub-pieces while adding more variety of similar objects to the new groupings. I've paused service for new downloads on this older version of the catalog in anticipation of transitioning to the updated catalog in the next few months.

The Women\u2019s Professional Billiard Association (WPBA) is the governing body of women\u2019s professional billiards in the U.S.A., and one of the longest-running women's professional sports organizations in the world.

The script behaves as expected, printing "ok!" and ending. But if I omit the if __name__=='__main__': line and de-indent the following lines, my machine (OS X) goes crazy, continually spawning tons of Python processes until I killall Python. Any idea what's going on here?

That means that the library will need to spawn (instead of fork) your child process, and have it re-import the __main__ module to run f, just like Windows does. Without the if __name__ ... guard, re-importing the __main__ module in the children will also mean re-running your code that creates the billiard.Process, which creates an infinite loop.

You should do your own for billiards honestly and I bet its has lots of raycasts in the end, which in turn give you the shot line UI that you see in most of them. Its kinda hard to do things like english on the ball with Oimo and Cannon.

Ammo.js works imho. It all depends on the level of accuracy you need, but, you can get something good with ammo. Here is an example I have built . Not exactly billiards, but, the physics are quite similar.

Overall, the fifty objects clearly demonstrate that this narrowly circumscribed part of New York State has played an astonishing role in shaping the history of the nation and, in several instances, the world beyond the confines of our national borders.

In 1875, the Scottish immigrant Peter Kinnear took over the billiard ball manufacturing business and changed the name to Albany Billiard Ball Company. At the time, the factory was located on the southeast corner of Grand and Plain Streets in Albany (now under the South Mall Arterial). Kinnear and others encountered one major problem: celluloid tended to explode into flames. Fortunately, another early plastic developed by Hyatt, called bonsilate, was better suited for billiard balls. Made from finely ground bone and sodium silicate, bonsilate was sturdier than celluloid, held color better, and did not burst into flames. Kinnear quickly adopted the composition as the primary material for his billiard balls.

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