Coin-op pool tables

Ok, the other day, I was at a bar and grille, and they had a coin-operated pool table there. If you hit a ball into a pocket, the table trapped it, until you put in another buck, but if you accidentally pocketed the cue ball, it spat it back out. What I’m wondering is, how does it tell the difference? My best guesses are:
1: The cue ballhas a slightly different mass, radius, or moment of inertia from the other balls. This could account for the sorting, but it would also change the play of the game, probably noticeably, above the table.
2: There’s some sort of device in the table that “looks” at the ball, and picks it out based on color. Fine, except that I don’t think that the technology for this existed when these tables were first made.
3: The cue ball contains iron, and is sorted magnetically. Somehow, I don’t think that they do this…

Any other guesses, or confirmation for any of these?

The cue ball is slightly smaller than the other balls. There’s an amusing story about this at Darwin Awards: http://DarwinAwards.com/cgi-bin/frames.cgi?/darwin/darwin1999-30.html

I always thought it was by weight, but I found the following in a coin-op pool table ad:

They seem to be pushing their magnetic system as superior to one with a cue ball of slightly different size. I suppose you could go to your local bar with a set of calipers, a scale, and a magnet.

Even if it results in a ball of the same size and weight, putting a ball bearing or something in the middle of the cue ball is going to change the weight distribution, and thus the characteristics of the ball when it comes to applying English.

But, then again, who’s going to notice on your average bar table?

Yeah, “moment of inertia” is the scientific term for the distribution of the mass, and it would be possible to make a magnetic ball with the same mass, volume, and moment of inertia, if you put the right amount of iron in at the right depth and made the compensating hole in the middle the right size. If you did that, then the cue could be made to behave exactly like the other balls, in the absence of a magnetic field.

On bar tables, the cue ball is actually larger than the other balls. As a result, in a bar, it’s easier to apply “follow”, where you apply a forward spin on the cue ball, so it’s spinning faster than it’s rolling, and after contact with another ball will continue to roll forward. Likewise, on a non-coin table (where the cue ball is smaller), it’s easier to apply “draw” or backspin, causing the cue ball to roll backwards after contacting another ball.

Personally, I don’t care for larger cue balls. I have a much better time controlling the cue ball when it’s smaller.

So how do we take advantage of the magnetic qualities of the new cueballs? Hm…

bille, I have played on way more of my fair share of coin op tables, and out of my own curiosity (as in the OP) noticed that the cue balls were SMALLER on the coin op tables.

A reglation pool table should have the cue ball the same size as the others, it allows for greater accuracy ie the cue ball will contact the EXACT center of the object ball (if you want it to of course)

All these answers are correct. Some tables use larger balls, others use smaller balls, and some use the magnetic trick.

The larger and smaller cue balls change the game quite a bit. The larger cueballs are often heavier, which changes the rebound angle after two balls collide. If the cueball is larger than the object balls, it can be nearly impossible to cut a ball into a pocket if it is resting on the rail (the trick to this one is to aim the cueball to miss slightly, and only contact after it’s already sunk into the rail a bit).

All the ones I’ve ever seen were larger than the object balls. I recall entering a pool tournament four or five years ago, and my game at the time was generally very good. But the tournament was played on coin-op tables, and the larger cue ball size really threw off my estimate of the required angles. I didn’t do very well.

Aha, so it does usually change the gameplay, and bars just don’t care! I suppose that if you get enough beers into a player, you could use a basketball for the cue and it wouldn’t matter much… I do like the magnetic idea, though… I wonder if I could sneak one of those 20 Tesla electromagnets from the lab into the bar?

Try a roll of 40+ ga enameled wire, a 6v gel cell (I’ve seen surplus 24AH units that are pocket-sized for under $20) and a doorbell button – instant electromagnet.

Just look up the resistance and current capacity of the wire you choose. If your wire isn’t long enough to keep total resistance under the current capacity… yowch! Meltdown!

Not that I’d actually condone such chicanery