Squirt. End Mass and Cue Flexibility.

It moves from stored kinetic energy....duh...

Corwyn_8 said:

Given that how do you explain a rubber ball hitting the floor and bouncing back up. If no force is being applied as the ball decompresses how does it move?

Thank you kindly.

Click to expand...

The energy is stored in the rubber of the ball from the impact with the ground...The ground has already imparted the energy for the ball to bounce back up.

Jaden

Jaden said:

How does an object that is moving away from another object receive force from that object?

If the tip is decompressing, the ball is moving away faster than it, there is no objectivity to that statement. It is FACT.

So again, how does an object impart force to an object that is moving away from it?

Jaden

Click to expand...

It's not obvious to me at what point it is moving away from the tip faster than the tip is expanding, but what seems obvious to me is that peak force would have to be at maximum compression....and sometime later that has to go down to zero force. Somewhere in between, the tip is decompressing yet is still pushing on the cue ball or else you would go from peak force to zero force with nothing in between. Classical physics doesn't generally have discontinuities like that.

Even if you know absolutely nothing about classical physics, you should be able to reason through that:

1) the tip compresses the most when it's pushing the most
2) sometime later, the force eventually drops to zero
3) in between, there's a time when the tip is expanding while the force is smoothly dropping to zero

Corwyn_8 said:

Can we unpack that statement a bit?
1) When you say you can control it better, are you talking about subsequent shots? Or are you saying that you "feel" the shot, make a decision, and change something?

2) What aspects of the cue ball trajectory are you controlling, based on that feel?

3) I can understand "different" feel, but I have no idea what "more" feel means (in this context). Can you describe?

Thank you kindly.

Click to expand...

"Feel" to each person is DIFFERENT! It is hard to explain feelings.

I will "try" to explain what I think happens with "ME".

I have played for 50 years or more and I have had numerous cues, both production and custom.

I learned with a tip that ranged from the softer side to something that was probably medium hard and that "feel" is engrained into my "muscle memory".

When I hit with "my" tip, the "feedback" lets me "know" how hard or soft I have hit the ball because I can "evaluate" the feedback against what I already know from previous shots. I also can feel if I have hit closer to the center of the ball because it feels "heavier" when I hit dead center. I think the millisecond longer contact time has something to do with it. Some may say this is BS, but I can line up numerous players who play at an "A" or higher level who will tell you the same thing.

Some will call it "hit" or something else...to each, their own.

If I play with a tip that "rebounds" the ball at rocket speed, it doesn't give me the same "control", because it isn't what my muscle memory is accustomed to and the "feel" and "sound" is different.

I'll let the scientists on here debate whether that is a fact or not, but in my mind that is the way it works with "ME".

yes that is correct.

john coloccia said:

It's not obvious to me at what point it is moving away from the tip faster than the tip is expanding, but what seems obvious to me is that peak force would have to be at maximum compression....and sometimes later that has to go down to zero force. Somewhere in between, the tip is decompressing yet is still pushing on the cue ball or else you would go from peak force to zero force with nothing in between, classical physics doesn't generally have discontinuities like that.

Click to expand...

There is a point where the force becomes net zero and it isn't immediately after compression. I acknowledge that. It is pushing back initially but not for the entirety of contact.

Jaden

Jaden said:

So again, how does an object impart force to an object that is moving away from it?

Click to expand...

Consider the rubber ball again. It is decompressing, it is exerting a force on the ground, the ground is exerting a force on it (of the same magnitude, but opposite direction). How else would it get back into the air?

Thus the ground is imparting a force to an object that is moving away from it.

Thank you kindly.

Jaden said:

The energy is stored in the rubber of the ball from the impact with the ground...The ground has already imparted the energy for the ball to bounce back up.

Click to expand...

Ok. So now squeeze a ball in your hand, and release it, why doesn't it jump up? It is compressed just as if it hit the ground.

Thank you kindly.

Jaden said:

There is a point where the force becomes net zero and it isn't immediately after compression. I acknowledge that. It is pushing back initially but not for the entirety of contact.

Jaden

Click to expand...

Well, that just has to do with the resiliency of the tip. Different materials will yield different results. I have no idea how a leather tip springs back. There's no fundamental physical reason why it would have to be so, though, other than at the very tippy end of the decompression...because if not, the tip would fly apart, so clearly it's slowing down on it's own. How much, starting where, etc is a physical property of the tip and nothing else, really.

But if it's in contact, it really must still be pushing, and I can give a bit of a nuanced argument why if you're interested.

For the tip to be in contact with the cue ball, yet impart no force, it must be expanding at precisely the same rate that the cue ball is traveling. Let's neglect friction, because we know that all this happens in a very short amount of time, and slowing down due to friction is negligible (and will actually only slant the problem more in my favor).

We already know that the rate the tip expands MUST go back down to zero very quickly, or else the tip flies apart. So think about this: for the tip to be in contact and not push, it must be traveling at constant velocity to just barely keep up with the cue ball. That would be an incredible coincidence. What really happens is that any time the tip is in contact, it IS pushing. The only reason they're still in contact is that the tip is pushing on the cue ball, and the cue ball's not getting out of the way fast enough. There's a instant in there where the tip's velocity (due to the being on the cue + it's expansion) finally slows up enough that the cue ball skitters away, but it's overwhelmingly likely that any time the tip and cue ball are in contact they're pushing on each other because it would require theoretical perfection for it to happen any other way.

I hope that makes sense. I know it's not easy to follow and is kind of a hand wavy sort of argument, not a proof.

HawaiianEye said:

I think the millisecond longer contact time has something to do with it. Some may say this is BS, but I can line up numerous players who play at an "A" or higher level who will tell you the same thing.

Click to expand...

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.

Jaden said:

For any mass to be MOVED, there HAS to be enough force to move it.

Click to expand...

If the mass is floating in space, any force, no matter how small, will move it immediately. If it's sitting on a table here on earth, however, the force will have to build up until static friction is overcome. So you're sort of right in that respect, but it's the fiction and not the mass that causes the delay, as John Coloccia has been pointing out.

Jaden said:

If the force necessary to move it is less than the force it takes to deform the tip, guess what? the tip will deform prior to the mass being moved.

Click to expand...

I think you meant "more," (but I would never nitpick).

Jaden said:

This is because of inertia preventing the object with mass from moving until acted upon by enough force to move its mass. You don't have to factor in any calculation for inertia just like you don't have to factor in any calculation for gravity even though gravity is what is holding the objects to the table.

If you can't even see that, then you need to give up now.

Click to expand...

Maybe not a bad idea?

Jim

Jaden said:

There is a point where the force becomes net zero and it isn't immediately after compression. I acknowledge that. It is pushing back initially but not for the entirety of contact.

Click to expand...

Then what is maintaining contact?

Thank you kindly.

john coloccia said:

But if it's in contact, it really must still be pushing, and I can give a bit of a nuanced argument why if you're interested.

Click to expand...

I have a another argument: "Contact" can not be defined at a sufficiently precise level, without being aware of the existence of forces between the objects.

Do Atoms ever touch

Thank you kindly.

john coloccia said:

I have no idea how a leather tip springs back.

Click to expand...

I think you do. Imagine instead of a leather tip, we used a tip made of phenolic instead. I bet you imagined that it would act just like a ball-to-ball interaction (i.e. high squirt, low spin transfer, etc). Now imagine instead a tip made of crumpled paper. I bet you imagined the cue ball not moving much at all and the cue crashing into it like a car crash, both object moving together at their average momentums. A leather tip is somewhere in between (closer to the phenolic).

Thank you kindly.

Jal said:

If the mass is floating in space, any force, no matter how small, will move it immediately.

Click to expand...

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.

If it's sitting on a table here on earth, however, the force will have to build up until static friction is overcome.

Click to expand...

It is EXACTLY the same case here. The first atoms move, then the next. Atoms stuck to the table might not move, and the wave bounces back, and further force (i.e. more atoms, moving further) will be required to break those bonds.

We know there is a force, which means we know that some mass is accelerating, it just happens to be atoms, not objects.

Thank you kindly.

Bob Jewett said:

Except that the fact the ball is constrained only at the bottom will allow it to move immediately (and rotate). But the static friction (about an ounce) is negligible compared to the typical peak force from the tip (about 1000 ounces).

Click to expand...

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

I think Jaden might have come to believe that's it's mass that causes a delay from pushing around, say, refrigerators and the like - thus the point about static friction.

Jim

Corwyn_8 said:

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.

Click to expand...

Yes and no.

If you apply a force to an object, its center of mass accelerates immediately according to: a = F/m. If, for instance, you designate a swarm of rocks stretching from here to the nearest star as an 'object,' and push on just one of the rocks near the earth, the center of mass of the entire swarm will accelerate according to F/M, where M is the sum of all the individual masses. This isn't a violation of relativity, but comes from the definition of center of mass (a weighted average of the mass distribution). (There is a relativistic version of F/M, but we're talking about small velocities).

In that respect, the object does accelerate instantly. But, as you say, it's certainly true that only the parts of the object in intimate contact with the driving force move "immediately." The rest of the parts will take time to catch up to the center of mass (assuming they're all joined together).

Jim

Jaden said:

The ground has already imparted the energy for the ball to bounce back up.

Click to expand...

Energy is not the same thing as force.

As an aside, the ground did not impart any energy to the ball. If it did where did it come from? Why is the ground WARMER than it was before and not COLDER, which it would be, if it just gave up energy (rather than gained it).

You are going to have a hard time understanding this if you don't get a clearer picture of where the energy is in this scenario. It starts as gravitational potential energy in the ball. Changes to kinetic as the ball falls, converts to spring energy in the ball (and thermal energy in the ball and ground), and back to kinetic energy of the ball traveling upwards, and back to potential energy at the top of the bounce.

Thank you kindly.