Squirt. End Mass and Cue Flexibility.

Yes and no. :)

If you apply a force to an object, its center of mass...

Thus proving nothing more than that some arbitrary center of mass isn't in any meaningful sense, 'the object'. Would you claim that in the interaction we are discussing we should be using the center of mass of the table (and balls)?

Thank you kindly.
 
Technically no. The force can only be felt by any particular atom after it has traveled to the place that atom is at the speed of sound in that material. So, the first atoms start to move immediately, the next atoms move when they feel the force of the first atoms moving, and so on. ...

Well, it's true that the force between the tip and the ball has to propagate (in sound waves) to the nether reaches of each object before such reaches can participate in the collision, and to do the analysis completely we need to use a tool at least as complicated as finite element analysis, but the times involved are such that the compression waves have plenty of time to alert all parts of the objects during the tip-ball contact time and a simpler "rigid body" analysis seems to be satisfactory for most requirements.
 
You seem to be under the false impression that force is being imparted during the entirety of tip contact, but it's not. It's only being imparted while the tip is being compressed. As soon as the tip starts to decompress, the force ceases to be imparted between the ball and the tip/shaft.
Jaden,

I hope you are "pulling my leg" with this, because we have been through this ad nauseum.

This is an extremely basic principle of physics. If the tip is compressed and still in contact with the CB (even if it is in the decompression stage), then there must be a force between the tip and CB.

Here's one more try:

A tip behaves like a spring. Force is directly related to compression (F = kx). If the tip is compressed a little, it is because there is a small force acting on it. If it is compressed a lot, it is because there is a large force acting on it. When the tip first touches the CB, there is no compression at all, and no force. As the cue continues to move forward, the tip begins to compress gradually. This results in an equal and opposite force on the tip and CB that also increases gradually. The CB begins to accelerate as soon as there is a force acting on it (F = ma). The CB accelerates slowly at first since the force is small, but as the tip compresses more and more, the CB accelerates faster and faster. When the tip reaches full compression, the force between the tip and CB is at its peak, and the CB is accelerating at its fastest rate. As the CB begins to move faster than the tip, the tip begins to spring back and the force between the tip and CB starts to decrease in proportion to how much it is still compressed. The force is maximum at the beginning of the decompression and is zero after the tip has fully decompressed (as it is about to release from the CB), but there is force acting between the tip and CB during the entire spring-back or decompression stage. The force continues to cause the CB to accelerate forward this entire time (until the tip totally releases from the CB).

FYI, I think all of these effects are evident (with an open mind) in the high-speed video and images on the squirt endmass and stiffness effects resource page.

The tip MIGHT be imparting lateral force to the BALL, but the ball definitely isn't imparting any lateral force to the tip/shaft.
Jaden,

This is another fundamental flaw in your thinking that again violates a very basic foundational principle of physics (Newton's third Law of Motion): "For every action, there is an equal and opposite reaction." In other words, if the tip is exerting a force on the CB, the CB must also be exerting an equal and opposite force on the tip. This applies in all directions (longitudinal and lateral).

Also, if the CB deflects from the line of the shot, and the endmass moves laterally in the opposite direction (both of which are clearly visible in the videos, illustrations, and analyses), there must be an equal and opposite lateral force acting between the tip and CB.

Again, the two main premises of your way of thinking on this topic are absolutely wrong. This isn't my opinion ... it is fact, based on extremely basic and simple physics principles.

I hope my efforts at least make you reconsider your premises. And I hope the video and images help you visualize these effects. I would also recommend you carefully read through everything on the following resource pages (even if you have carefully read through them in the past) with as open a mind as possible:

what causes squirt

squirt endmass and stiffness effects

It won't help one bit if you continue to keep telling me my premises are wrong (because they are based on very basic and sound physics principles). It also won't help to keep repeating your incorrect premises and drawing incorrect conclusions from them.

Regards,
Dave
 
Why do you think this? We all agree that different cues have different feel. What makes you think that it is the contact time IN PARTICULAR that makes the difference in what you feel? Why that and NOT efficiency (for example)?

Thank you kindly.

I could ask you the same question in reverse.

Why do you, or anybody else, think that is not the case?

You asked me what I "thought" and I told you.

I "think" that "I" can "feel" the difference in the time.

If there was no "feel" involved, then there wouldn't be a cue trading market, or different tips, etc., etc., etc.

My background is in "communications", FWIW, and I feel that people "communicate" with their cue (and some cues don't listen...LOL). The more you can "feel" what is happening with your cue, the more you are able to determine what is "right" and what is "wrong" when you hit a ball.

I have known car mechanics who could put their hand on the hood of your car and tell you if it wasn't running properly because of the vibration.

Believe it or not...I believe it.

I can't control what anybody else believes.

Aloha

http://www.eatonhand.com/hw/facts.htm

Hand and Brain
"About a quarter of the motor cortex in the human brain (the part of the brain which controls all movement in the body) is devoted to the muscles of the hands. This is usually illustrated with a drawing of a human figure draped over the side of the brain, body parts sized proportional to the amount of brain devoted to their movement, referred to as a homunculus - as illustrated in this drawing from Dr. Wilder Penfield's monograph "The Cerebral Cortex of Man.":

Fingernail feeling
"Do fingernails have feeling? No, but the fingernail extends deep beneath and behind the skin of the cuticle, and nerves on the back of the finger around the cuticle sense forces transmitted from the tip of the fingernail. The brain integrates the sensations from the nerves of both the fingertip pad and cuticle to give a complex enhanced perception of pressure and shear at the fingertips. Loss of a fingernail changes the feeling on the palm side of the fingertip."

http://www.isciencetimes.com/articl...human-touch-new-research-suggests-fingers.htm

"This means that, if your finger was the size of the Earth, you could feel the difference between houses from cars," Mark Rutland, Professor of Surface Chemistry at the institute and one of the authors of the new study on human touch, said in a press release. "That is one of the most enjoyable aspects of this research. We discovered that a human being can feel a bump corresponding to the size of a very large molecule."

http://www.science20.com/news_articles/sense_touch_uses_vibrations_just_hearing-98781

Researchers have known for years that these afferents respond to skin vibrations, but they studied their responses using so-called sinusoidal waves, which are smooth, repetitive patterns. These perfectly uniform vibrations can be produced in a lab, but the kinds of vibrations produced in the skin by touching surfaces in the real world are messy and erratic.

For this study, Bensmaia and his team used a vibratory motor that can produce any complex vibration they want. In the first experiment, they recorded afferent responses to a variety of frequencies in rhesus macaques, whose tactile nervous system closely resembles humans. In the second part, a group of human subjects reported how similar or different two particular frequencies felt when a probe attached to the motor touched their skin.

When the team analyzed the data recorded from the rhesus macaques, they found that not only did the nerve oscillate at the frequency of the vibrations, but they could also predict how the human subjects would perceive vibrations based on the neuronal responses to the same frequencies in the macaques.

"In this paper, we showed that the timing of spikes evoked by naturalistic vibrations matters, not just for artificial stimuli in the lab," Bensmaia said. "It's actually true for the kinds of stimuli that you would experience in everyday life."

What this means is that given a certain texture, we know the frequency of vibrations it will produce in the skin, and subsequently in the nerve.

In other words, if you knew the frequency of silk as your finger passes over it, you could reproduce the feeling by stimulating the nerves with that same frequency without ever touching the fabric.

But this study is just part of ongoing research for Bensmaia's team on how humans incorporate our sense of touch into more sophisticated concepts like texture, shape, and motion.

http://www.science20.com/news_articles/sense_touch_uses_vibrations_just_hearing-98781

Researchers could someday use this model of timing and frequency of afferent responses to simulate the sensation of texture for an amputee by "replaying" the vibrations produced in an artificial limb as it explores a textured surface by electrically stimulating the nerve at the corresponding frequencies. It could also be used for haptic rendering, or producing the tactile feel of a virtual object on a touchscreen (think turning your iPad into a device for reading Braille, or controlling robotic surgery).

"We're trying to build a theory of what makes things feel the way they feel," Bensmaia said. "This is the beginning of a story that's really going to change the way people think about the somatosensory system."

https://books.google.com/books?id=g...epage&q=can the hand timing vibration&f=false
 
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^^^^^^^^^^^^^^^^^^^^^^^^^

:thumbup2:

Interesting & we are very complex bio-mechanical entities.

To take our boi-mechanical aspects out of the equation is a mistake IMO.

We obviously 'feel' the collision & thus we at the very least subconsciously react to it in some manner.
 
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I said:

"I would guess that on a hit below center (draw), there ought to be an ever so slight delay (miniscule) from cloth friction?"

So the analysis would be with a small force applied at, say .3 of the ball's height and the bottom of the ball stuck to the cloth. I think that results in the somewhat counter-intuitive result of the ball getting a little follow. Going back to pushing the door, this would be like pushing on it a few inches from the hinges. The door will still move. It only will remain stationary if you push right at the hinges (= base of the ball).
Bob, I stand corrected. Thanks for getting me to think about the inevitable effect of applying a torque above the point of contact with the cloth.

Jim
 
Thus proving nothing more than that some arbitrary center of mass isn't in any meaningful sense, 'the object'. Would you claim that in the interaction we are discussing we should be using the center of mass of the table (and balls)?
I don't think the center of mass of an object is some arbitrary attribute. If you ask where an object is located or how fast it's moving, physics-wise, I think its center of mass is the most natural thing to choose. This is especially true if its individual parts are undergoing all sorts of gyrations.

I'm not sure at this point what interaction you're referring to. I brought up the center of mass thing in reference to a free standing object.

Jim
 
Bob, I stand corrected. Thanks for getting me to think about the inevitable effect of applying a torque above the point of contact with the cloth.
Jim,

Good job setting a positive example by admitting that an idea or premise that is in conflict with a basic Law of Physics probably needs to be rethunk.

Hopefully, others who might have ideas in violation of basic Laws of Physics will learn from your example.

Regards,
Dave

PS: I know ... I'm being overly optimistic.
 
Does the resistance of the CB mass make the tip compress & the shaft bow with the tip pointing in...

or does it simply bounce off & deflect off away from the center of the CB mass?

Does the tip & cue stick swipe to the outside of the ball as the bowed shaft restores itself from being bowed with the tip pointing in toward the center of the ball...

Or...

do they do both?

Do they do both 'simultaneously' or do they restore themselves first & then bounce off & deflect away from the center mass of the CB?

Do the compressed tip & bowed shaft restore themselves & help to push the cue ball away?

Do the tip & shaft then travel outward away from the center CB mass?

Do they start to bounce & deflect off first & then restore themselves as they continue to move to the side?




If a cue stick travels straight through on a side of the center line where a cue ball once sat would the ball squirt be at the highest degree?

If the total forces & parameters involved are such that the capacity for the cue stick to travel straight through on a side of the center line is diminished & it is by some means sent away for the center of the cue ball's mass would the squirt angle be reduced?

If two cue sticks were identical in their weight distribution but one was more flexible than the other would the one that is more flexible yield less CB squirt angle?

If the two cue sticks had identical flex characteristics but one had a lighter front end would it yield less CB squirt angle?

If one of the two cue sticks had both greater flex characteristics AND a lighter front end would it yield even less CB squirt angle than either of the other two scenarios?

Just some rhetorical food for thought for anyone so inclined.
 
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Good job setting a positive example by admitting that an idea or premise that is in conflict with a basic Law of Physics probably needs to be rethunk.
I've gotten a lot of practice in this thread....wasn't exactly looking for any, though. :)

Jim
 
a simpler "rigid body" analysis seems to be satisfactory for most requirements.

Of course. As long as one doesn't try to say things like the body isn't moving and the force is 'building up'. Which is where I saw the argument going.

Thank you kindly.
 
Why do you, or anybody else, think that is not the case?

What makes you think I think it is not the case?

You asked me what I "thought" and I told you.
I "think" that "I" can "feel" the difference in the time.

No, actually you didn't say that. You said it felt different, and attributed that to the contact time. And you certainly didn't say HOW you knew it was the time.

So you are saying that you are able to detect both the initiation and cessation of contact between the tip and ball, and measure the difference to within less than 0.001 seconds. And that you have tested this to determine that this is what you are feeling and not some other aspect of the interaction, like efficiency.

Awesome. Can you please explain how you did that?

My background is in "communications", FWIW

Terrific, so there should be no problems with communication this information to us.

Thank you kindly.
 
I wouldn't discount being able to feel a difference on the order of a millisecond. The human ear, even my ears that have been damaged from years of being a musician, can hear well into the kiloHertz. SOMETHING in your brain can certainly process information that quickly, and we also know that our hearing is quite sensitive to small delays between when a sound hits the individual ears....certainly under a millisecond.

Anyhow, I wouldn't just toss it out because it seems like you shouldn't be able to feel something that short. We routinely process at least some physical stimuli that quickly.
 
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You've said this before.

I don't know the man. He's probably a great guy and sells some good products. But you're referencing a person who says the tip contact time can be 4ms and/or 7mm :eek:

Likely because he has read my previous posts and links.... I will continue to say 4ms and not bat an eye until I have high speed video that disproves it....

http://dbkcues.ru/2011/06/12/another-couple-of-hs-video-now-24-000-fps/?lang=en

This is the test that I suspect caused the change to the information on Dr Dave's resource page... Notice it is Hard vs Medium NOT SOFT... and you are up to 2ms already..(Dave's info has a soft at 2ms).... A medium tips spring rate is about 8% less than a hard tip on average and you have already doubled contact time...

It would follow if the spring rates continue to drop then the contact should continue to increase... So a Soft tip may end up at 3ms and a true super soft like the one used by Blackboar on their ferule-less LD shaft may indeed reach 4ms.. I have played around with making the super softs and they are 15% less than a medium.....
 
What makes you think I think it is not the case?



No, actually you didn't say that. You said it felt different, and attributed that to the contact time. And you certainly didn't say HOW you knew it was the time.

So you are saying that you are able to detect both the initiation and cessation of contact between the tip and ball, and measure the difference to within less than 0.001 seconds. And that you have tested this to determine that this is what you are feeling and not some other aspect of the interaction, like efficiency.

Awesome. Can you please explain how you did that?



Terrific, so there should be no problems with communication this information to us.

Thank you kindly.

If you come to Hawaii, I'll be happy to converse with you all day about it, but I don't have a stenographer so I'm not going to try to write textbooks on here with this little iPad keyboard.

Believe what you want to believe. Whether you believe has no effect on me or my game.

You asked me what I thought and I answered you.

Aloha
 
I wouldn't discount being able to feel a difference on the order of a millisecond. The human ear, even my ears that have been damaged from years of being a musician, can hear well into the kiloHertz. SOMETHING in your brain can certainly process information that quickly, and we also know that our hearing is quite sensitive to small delays between when a sound hits the individual ears....certainly under a millisecond.

Anyhow, I wouldn't just toss it out because it seems like you shouldn't be able to feel something that short. We routinely process at least some physical stimuli that quickly.

I don't play an instrument, but I agree with you.

Explaining colors to a colorblind person is hard also, when shades of different colors all look the same to them.

It would be like trying to explain the following link to some people.


https://www.reddit.com/r/askscience...oes_plucking_a_guitar_string_harder_not_make/
 
Originally Posted by LAMas
-" The tip compresses before the CB moves."


.......

I'm puzzled by this statement. I hope you realize that if there has been force to compress the tip that same force has started cue ball movement. They must occur at the same time.

This is very, very basic physics.

My conclusion is that since the cue ball is just beginning its acceleration, the distance moved is small and the photography is not good enough to capture the small movement that has taken place
Bob Jewett
SF Billiard Academy


Here is an old high speed vid. The tip is being compressed a bit before the CB rotates or moves forward.

https://www.youtube.com/watch?v=DceJZs2AJgQ

What do you see?
 
Originally Posted by LAMas
-" The tip compresses before the CB moves."


.......

I'm puzzled by this statement. I hope you realize that if there has been force to compress the tip that same force has started cue ball movement. They must occur at the same time.

This is very, very basic physics.

My conclusion is that since the cue ball is just beginning its acceleration, the distance moved is small and the photography is not good enough to capture the small movement that has taken place
Bob Jewett
SF Billiard Academy


Here is an old high speed vid. The tip is being compressed a bit before the CB rotates or moves forward.

https://www.youtube.com/watch?v=DceJZs2AJgQ

What do you see?
My conclusion from the video is that the initial motion of the cue ball is hard to see because it is accelerating from zero and since the force from the tip will be increasing more or less linearly, the velocity will be increasing as the second power and the displacement as the third power.
 
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