Contact point

[sfleinen]

Wher do I get Carbon Paper???

I'd say its smaller than I can see. Even with my glasses on.

3kushn:

Any office supply store (e.g. Staples, Office Max, Office Depot, et al.) carries this stuff:

http://en.wikipedia.org/wiki/Carbon_paper

Cut it into 1" x 2.5" strips. Stand a strip right up on end up against the object ball, coating-side against the object ball, and shoot the cue ball right into the middle of the strip, basically squashing it against the object ball. Try this at different speeds. Be sure, after every shot, to rotate the object ball to a clean area and stand up a fresh strip against that clean spot on the object ball. I'd recommend shooting the object ball into a pillow on the table, and not into a pocket or a cushion, so that the carbon spot on the object ball isn't rubbed off or smudged when it hits the inside of the pocket, or the cushion.

Again, try different speeds. You'll be surprised at the findings.

-Sean
-Sean

 

[chipperd]

contact point

The size of the contact point where the cueball makes contact with the object ball depends on the distance of the object ball from the pocket. For instance if the object ball is sitting in front of the pocket, the contact point is very big. If you have to shoot the object ball eight foot from the pocket and you miss the contact point by 1/8 of an inch, you will probably miss the pocket by a foot.:wink:

 

[3kushn]

The "POINT", I was trying to make here is that the area is very small. Of course when the object ball is very close to the pocket you have a greater area on the object-ball that can be hit and still pocket the ball.

What you should do is put two balls together, I recomend lighter colored balls, one, three or five, and look at the point in the light. Roll the balls around each other and see that the area never changes. It's still small. Exact measurement, I really don't know.

All I know is the farther away from the pocket the object ball is, the more precise you have to be on your shots. EXAMPLE: IF YOU START A SPACESHIP OUT TO GO TO THE MOON AND IT"S ONE MILLIONTH OF ONE DEGREE OFF COURSE, THEY MIGHT END UP ON JUPITOR.

When you miss the same shots the same way you might want to take this into consideration. The adjustment to make that particular shot is going to be a very small area.

As far as the balls compressing, I have a hard time believing this happens. The ball would be rolling like it had a flat tire. Believe what you want to believe. That's just my theory.


__________________________________

http://tommcgonaglerightoncue.com

Not to be argumentative but the contact surface area doesn't change because there's a greater or shorter distance but difficulty hitting the correct spot increases as the distance increases.

As far as the balls deforming here's a shot that's made by jumping but sometimes the situation seems the ball must flex like a water balloon cause you can't see the OB jump. I know. Makes very little sense.

CueTable Help

 

[Bob Jewett]

A few points:

The accuracy required to make a shot has nothing to do with the size of the contact patch. People who don't understand the physics/geometry of the collision might think they are related, but they're not.

The contact patch is about 1/4-inch in diameter, but this depends on the speed of the shot.

If anyone is interested in the theory, search for Hertz's Law which is the part of physics that tells you about how spheres collide. Here is a non-technical article from about 10 years ago.

 

[desmocourtney]

Bob,

What is the answer to the quiz at the end?

I am guessing the ball compression narrows the angle.

Thanks
Courtney

 

[TheBook]

Depends on the speed, Tom. We're using plastic balls these days, so the harder you hit, the larger the contact point (due to compression and snap-back). A piece of carbon paper placed between the two balls proves this -- the harder you hit, the larger the carbon mark on the ball.

Now, where do I pick up my $1.00 off coupon for a Subway sandwich?

-Sean

I also saw this in a book but can't remember which one. The size increased according to how hard the balls collided. You wouldn't think that the balls would compress as much as they do.

 

[Bob Jewett]

Bob,

What is the answer to the quiz at the end?

I am guessing the ball compression narrows the angle.

Thanks
Courtney

I'll give the other readers a little more time with the puzzle before spilling the beans. Here is the question:

In 1887, the bright, young Mr. Hertz was
walking down a street in Berlin when he
heard an unfamiliar clicking sound coming
from a tavern. Entering, he saw a teacher
and a pupil and three ivory billiard balls.
Hertz had heard of this "billiards" but had
never seen a table before. The teacher shot
a simple carom — with the click that had
attracted Hertz — and explained the 90-
degree initial carom angle. Hertz piped up,
"But the angle between the paths of the
balls must be less than 90 degrees." How
did he know? For extra credit, what was his
mistake?​

 

[jsp]

How did he know?

The fact that the balls made a sound at impact proves that the collision isn't perfectly elastic (energy is lost making the sound), so the balls couldn't depart perfectly at 90 degrees but must be slightly less (all things being equal).

For extra credit, what was his mistake?

He made the assumption that the balls were perfectly equal (i.e. same exact weight and shape)?

EDIT: Oh, I know. His mistake was that he dedicated the rest of his life to science/engineering and not billiards. Duh. :duck: