Question(s) for Bob Jewett or Dr. Dave, perhaps?

[Rubik's Cube]

Good morning, gentlemen.

During a snooker world championship match today it was mentioned in commentary that should the cueball simultaneously strike a red and a colour it is deemed a foul.

The fact that anything very close might sometimes be difficult for the referee to judge accurately notwithstanding, it occurred to me that the white striking two balls at exactly the same time is probably unlikely.

My questions, sirs.

Would I be correct in that assumption?

And, if yes, is there a mathematical equation that proves the extreme rarity of a simultaneous hit?

Thank you.

 

[Patrick Johnson]

The fact that anything very close might sometimes be difficult for the referee to judge accurately notwithstanding, it occurred to me that the white striking two balls at exactly the same time is probably unlikely.

My questions, sirs.

Would I be correct in that assumption?

In pool "simultaneous" means "as far as the ref can tell".

pj <- actually Bob Jewett and Dr. Dave
chgo

 

[LowRight]

In pool "simultaneous" means "as far as the ref can tell".

pj <- actually Bob Jewett and Dr. Dave
chgo

That is the correct, practical answer. You'd have to examine the hit at the quantum level to actually see if the white "hits" them at the same time. I would think that would be exceedingly unlikely. And objects never really "touch" each other. Their electrons repel each other before they come into actual contact.

 

[WoodyJ]

As I understand it:

simultaneous hit in pool = goes to the shooter
simultaneous hit in snooker = goes to the opponent

I play both and shoot questionable shots in pool but not in snooker.

 

[Oikawa]

And, if yes, is there a mathematical equation that proves the extreme rarity of a simultaneous hit?

Simultaneous hit is a matter of definition. Practically speaking in a pool match, it is typically called simultaneous if the techniques at hand can't distinguish which ball hit first.

But as for what is actually happening, a truly simultaneous hit on a sub-atomic level, or whatever absurdly low scale fits best with your scientific worldview, will practically never happen. When the refs can't see the difference on a frame-by-frame analysis with whatever recording technology is available, it is for all practical purposes simultaneous.

 

[Biloxi Boy]

Without the ability to review, what does it matter in real life -- how are we to resolve a hit in question?

 

[Rubik's Cube]

The referees are permitted to use the video replay in professional snooker nowadays, and then amend their decision accordingly if necessary.

One would imagine the path of the cueball post collision is often a reliable indicator of which ball was hit first.

 

[Tennesseejoe]

Your assumption is that a simultaneous hit is probably unlikely. Yes it is probably unlikely but you can determine how unlikely it is.

Put a cue ball on the table, then freeze two object balls side by side about 1 foot in front of the cue ball. You now have a cue ball a foot away from the object balls that you are going to hit simultaneously. Now stand a flat head nail, flat side down, on the far side of the frozen balls...close as you can without touching the balls.
Now shoot the cue ball and try to knock the nail down. Do it 100 times. Keep track of your successes. That is your probability.

Willie Jopling set this up for a group for his presentation at the Derby City Classic for me to shoot. I did it on the first try, but not again that day.

 

[Bob Jewett]

It is usually possible to tell which ball was struck first.

Sometimes it's not possible. At snooker they seem to call that a simultaneous hit, but it usually isn't. At pool, it's called not possible to determine.

Here is the rule from snooker:

6. Hitting Two Balls Simultaneously Two balls, other than two Reds or a free ball and a ball on, must not be hit simultaneously by the first impact of the cue-ball.

Here is the corresponding rule for pool:

27. SPLIT HITS​

If the cue ball strikes a legal object ball and a non-legal object ball at approximately the same instant, and it cannot be determined which ball was hit first, it will be assumed that the legal target was struck first.

 

[Chopdoc]

Their electrons repel each other before they come into actual contact.

If you want to go that far, at the atomic level, the ball is mostly empty space. One could say they never actually touch. LOL!
Yes, I am being facetious, I don't need a physics lesson. LOL!

 

[Bob Jewett]

As for trying to achieve a simultaneous hit:

Place two object balls frozen. Place the cue ball along the common tangent to their point of contact. Shoot towards that point of contact trying to hit the balls simultaneously and use draw. If you draw the cue ball straight back to your tip, you have hit the balls simultaneously. If the cue ball comes back to one side about 45 degrees to the line of the cue stick, you hit one ball and then the other. If the cue ball comes back much straighter than 45 degrees to the side, the cue ball hit one of the balls first but then contacted the other ball while it was still touching the first ball.

I have managed to draw the cue ball back nearly straight in that situation when demonstrating close calls for a referees class. I have not gotten it to come back to my tip.

Now move the two object balls apart by not quite an inch, so that if the cue ball is placed touching them, the three balls form a right angle. (The exact distance between the two object balls is 0.932 inches, which is a little less than the diameter of a quarter dollar.)

Shoot the same shot between the balls with draw. Decide which ball was struck first.

 

[Biloxi Boy]

Shouldn't the shooter be obligated to make an obviously legal hit so that no foul could possibly result? If so, a shooter should lose all "ties". Make sense to anyone else?

 

[Bob Jewett]

Shouldn't the shooter be obligated to make an obviously legal hit so that no foul could possibly result? If so, a shooter should lose all "ties". Make sense to anyone else?

That's not an unreasonable way to play, and it is more or less how carom billiards works. The referee must be satisfied that a shot scored properly to award a point. (Fouls happen at carom a lot less often than close points.)

But I don't see any good reason to change pool from the current rule.

 

[maha]

since it is truly impossible to even get an exact hit and no way to call it. only call something you guess at. or an approximation.

so the only fair rule is if it isnt obvious which ball was hit first then the shooter gets it. which works both ways for all players so is the fair way.

 

[Amaury]

because the balls are deforming on impact, and a lot more than we think, I think simultaneous hits happen more often than we think.

 

[straightline]

because the balls are deforming on impact, and a lot more than we think, I think simultaneous hits happen more often than we think.

Depends how you round it off doesn't it? One nanosecond apart is still a difference. Anything indeterminate should be a non entity.

 

[maha]

since the opponent is the ref. if none is available, and he of course is biased, and so are many refs. which may be biased and neither can make a truly objective decision. all close ones should go to the shooter.
unless like in a money game if the opponent is concerned about say a good hit both the player and opponent will elect a third party prior to the shot to make the binding call.
its up to the opponent to call before the shot for a look at it, and not after.

 

[Bob Jewett]

because the balls are deforming on impact, and a lot more than we think, I think simultaneous hits happen more often than we think.

The ball-ball contact time has been measured. It is about a tenth of the tip/ball contact time, so around 100 to 200 microseconds.

I think there is a difference between contacts that are simultaneous and contact times that overlap. It is fairly easy to demonstrate overlapping contact times.