NV B.63 - Part 5: determining which ball was hit first - Pool Rules Quiz Instruction

http://billiards.colostate.edu

Instruction from Dr. Dave on how to interpret and apply pool shot rules in situations where it is important to know which ball is hit first.

Much more info can be found at:
http://billiards.colostate.edu

Category:

Sports

Tags:

• billiards
• pool
• rules
• fouls
• double
• hit
• frozen
• balls
• first
• contact
• rail
• push
• miscue

[oshua86]

however, for all the watchers out there you have created great videos, they are worth watching and instructional. I have really enjoyed them. good job.

[DrDaveBilliards]

@oshua86

Thanks. Please help spread the word about my vids, website, and instructional products.

[oshua86]

@DrDaveBilliards I have to all the new and "experienced" players in the league.

[DrDaveBilliards]

@oshua86

Thanks!

[oshua86]

right, I guess for the sake of pool instruction I can see your point, however; in pool they dont call it "the perpendicular line" they call it "tangent line" because pool balls are spheres.

"1.Geometry

A line which touches a circle or ellipse at just one point. Below, the blue line is a tangent to the circle c. Note the radius to the point of tangency is always perpendicular to the tangent line. "

[DrDaveBilliards]

@oshua86

That's one possible interpretation of "tangent line" (tangent to both spheres at the point of contact). However, I still think the more standard definition is: the line through the center of the ghost ball (CB position at OB impact) to which all post-collision CB paths are "tangent." I think this interpretation is the one used in most pool books and articles.

[oshua86]

@DrDaveBilliards I think I'm gonna have to email them and have them change the name from "tangent line" to "secant line" because any line that dissects a circle is a secant, it cant be a tangent ;)...

ohh god here is me being all difficult

[oshua86]

from a visual stand point, if you draw the tangent line at its exact point, the viewer would be able to see a greater deflection when the ball crosses the tangent line (top spin) or retraction from it (backspin).

[DrDaveBilliards]

@oshua86

Some people think the tangent line should be drawn through the point of contact of the two balls. Is that what you are referring to?

I prefer the more-standard definition: the tangent line is perpendicular to the line of centers through the center of the ball along the initial path of travel. All ball paths after impact (with stun, topspin, or bottom spin) are "tangent" to this line. It is better to show the path of a ball through its center.

[oshua86]

the tangent line is set up incorrectly every time in the video.