Forgot it was pool.
Ball never touches bottom of pocket
- Thread starter nataddrho
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High performance bowling balls are not homogenous spheres like pool balls. They contain cores that give the ball different moments of inertia about different axes, causing the gyroscopic precession due to the friction-drag moment as the ball slides and curves down the lane. Here's my shortened version of the podcast video, which has many visuals, illustrations, and demonstrations to go with the discussion:
Bob is correct. There is no gyroscopic motion in pool. This is clear mathematically in Euler's Equations of Rotational Motion, where all the gyroscopic terms are zero if the moments of inertia are equal.
However, the spin axis of a pool ball can most certainly change as the spin components change due to moments (or angular impulses during collisions) about different axes due to friction between balls or between the ball and the cloth on the table or rail cushions. Here's a good example:
That's not gyroscopic precession. It is just deceleration of one spin component.
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DeeDeeCues
Well-known member
Nah, once you spin the sphere the angular velocity creates gyroscopic effects.
Here’s a simpler description:
A curving bowling ball is like a massė shot in pool. But because a bowling ball is not a homogeneous sphere, its spin axis wobbles (due to gyroscopic effects), unlike with a pool ball. For more info and demonstrations, see:
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DeeDeeCues
Well-known member
Wow. Gyroscopic effect helps a spinning body to maintain a single axis of rotation, which reduces wobble.
Hence, using the fact that a bowling ball wobbles is actually counter to your argument.
Take a baseball pitch. The gyroscopic effect helps a fastball fly straight. A knuckler reduces spin and the ball curves and wobbles.
A baseball has raised seams that cut the air allowing movement on pitches. The spin, or lack thereof, doesn't contribute to the movement of a baseball. Try throwing a curveball with a smooth ball.
DeeDeeCues
Well-known member
Same phenomenon occurs with soccer balls, racquetballs, tennis balls....
I think you might be confusing the "gyroscopic effect" (e.g., precession) with a navigational "gyroscope." A gimbal-mounted gyroscope experiences no gyroscopic effects. The gyroscope maintains its spin axis because no torques/moments can occur through the gimbal. If there are no torques/moments, the angular momentum remains constant, so the spin axis does not change.
As is made clear in my video (and by Euler's Equations of Rotational Motion), a bowling ball's spin axis wobbles because it is not a homogenous sphere (i.e., it has different moments of inertia about different axes) and because the friction between the ball and the lane creates a moment/torque (about an axis different from the spin axis). Anytime there is torque/moment acting on an object with directional properties (like a non-homogeneous sphere), in a direction different from the spin axis, gyroscopic effects occur (hence the axis wobble).
Actually, a spinning baseball curves due to aerodynamic effects associated with the seams and the Magnus effect. A knuckle ball wobbles due to instability of the turbulent vortices shedding (and shifting direction) behind the ball. And none of this has anything at all to do with gyroscopic effects.
... because they are not smooth like a pool ball or bowling ball.
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Again, soccer balls and tennis balls aren't entirely smooth. Aerodynamics along with spin causes the movement. I've never played racquetball so I can't speak to that. It's possible because the ball is flexible, it is changing shape in flight which would cause a change in direction, especially when spin is induced. I suppose the same could be possible with a soccer ball and tennis ball.
Yes I get it Teach. lol...
DeeDeeCues
Well-known member
A person can easily find loads of references to gyroscopic effects on soccer balls and baseballs, cueballs, homogenous spheres of all types. Some which have been posted here.
You are missing overwhelming evidence because of your hypothesis bias.
Your bias is showing through a lot recently, like arguing that miscue double hits should be fouls. You are making the mistake of letting your bias get in the way of your 'science'.
DeeDeeCues
Well-known member
I never disputed that aerodynamics play a role.
Never said you did, just pointing it out.
You probably shouldn't trust everything you read on the Internet, especially things you are specifically looking for to to back up your beliefs, because you can always find the answers you want, regardless of your "alternative fact" beliefs. Also, some people might be using the phrase "gyroscopic effects" in a non-technical, informal way (i.e., not "properly"). I taught Advanced Dynamics at a graduate level for 30 years, so I know what "gyroscopic effects" really means, both intuitively and analytically, based on the official (math/physics) definition.
There is no bias in my suggesting miscues should be fouls because the video evidence (and an intuitive understanding of why the CB reacts the way it does with a miscue) proves that every clear miscue shot is technically a foul:
I honestly still do think it is ridiculous we penalize most clear push shots and double hits as fouls, but we make an exception and allow these fouls for miscues and scoops. However, due to the resistance people would have to a proposed rule change, I admit that it would not be a good course of action to change the rules. Rules should not be changed unless there is strong consensus, regardless of the facts. The best and most practical thing to do is to not change the rules that explicitly allow miscues and scoops even thought they technically are fouls.
DeeDeeCues
Well-known member
I don't trust everything I read on the internet, as is proven by my not trusting... you.
You have your thirty years of credentials, I'm not an expert on whether your credentials are valid, or what others with similar credentials think of your expertise. I only have one data point having worked with one of your former students who was about as useful as an engineer as a kitten is. Likely not your fault, but he held a degree from your institution.
As per the rules:. Rules should be changed to make a sport better, whether popular or not. Your proposed miscue rules would make pool almost unplayable without a well trained ref in every game.
You clearly aren't as interested in discussing science as you are in pretending to be a scientist. You have evaded the points raised in at least 3 scientific papers that were brought to your attention in this thread...one of which you have linked on your website on the physics of billiards. Instead you have chosen to pimp some of your YouTube videos on situations that are not applicable to case presented in the original post.
You and Neil Tyson are something else...you hide in plain sight...sometimes I get the scary feeling that even you believe your own hype.
Sad.
You and Dee Dee must have science credentials that put both of those science posers to shame. Let's see them.
pj <- ready to be impressed
chgo
Yo PJ, have you finished your Power Ranger coloring book yet?
That would be impressive.