Hmm. I've heard that since a hooking ball is still sliding, it will therefore deflect too much off the head pin. And what you are saying is the exact opposite. I'm confused now, but I do understand the sliding friction is much more than the rolling friction. Isn't the general consensus that the ball should stop hooking just before the pins?

Great topic by the way!

I think I can see the reasoning there. When the ball is rolling, it is easy to change the direction of the roll, because the only force to be overcome is the rolling COF. When it's still in its hook phase, the skidding COF is keeping it from deflecting, which is much higher.

I love threads like this.

That's exactly how I would describe it. The greater coefficient of friction will keep the ball from deflecting as much. Another thing to take into account is the difference between stopping hooking and rolling out. When the ball is first going down lane, it's motion down the lane is not in the same direction as the rotation of the ball. When the ball hits the friction, the balls slows down and the revs increase, as said earlier. Also, the ball's motion down lane starts to turn to match the direction of the rotation, in other words, hooks. Even if the ball has stopped hooking, the ball will still be sliding and increasing revs, but now in the same direction as the motion of the ball, so the ball drives through the pins. A ball that rolls out has not only stopped hooking but has also stopped revving up, so it no longer drives.

Mark

Ok, that was the part that got me confused. I didn't realize there was a difference between hooking out and rolling out. One of the top world coaches says that he prefers the term "hook out" to "roll out" as "roll out" would imply that the ball has stopped rolling. I therefore thought the two terms mean the same thing and I wasn't aware that the ball could have 0 axis rotation and still be sliding.

Hmm... but let's say a ball has lost all its axis rotation, is heading toward the head pin at an angle, but is still not rotating fast enough - so it's still sliding.

The force is acting in opposite direction of the ball's heading. At impact, the force of impact would also act on the ball in the same direction. Since the sliding friction force is greater than the rolling friction force, doesn't this mean the ball will deflect more if it's sliding?

I know where you're getting confused. Friction is a force that will always oppose the motion of an object. So, the friction force is opposing the motion of the ball moving forwards down lane, but that will not be too important for the next part. Now, look at what happens when the ball hits the pin. Let's say the ball hits the pin towards the right side of the pin. Part of that impact force will act to the right and try to accelerate the ball to the right. Thus, the friction force will act to the left to oppose the motion of the ball to the right due to deflection. If the ball is still sliding, the coefficent of friction between the ball and the lane is greater than if the ball is just rolling. Because the coefficient is greater when the ball is sliding, the ball experiences a greater friction force to the left to counteract the deflection and deflects less than the ball that is just rolling because the coefficient and then the friction force to counteract deflection is smaller.

A good analogy is a car on a perfectly level road. You accelerate up to 60 mph. Then, when the car has reached 60 mph, you shift into neutral and let the car stop on it's own, it will take a bit of time. Next, you once again increase to a velocity of 60 mph. This time, you press on the brakesa and the wheels lock up, assume no anti-lock brakes. The wheels will now be sliding, so the coefficient of sliding friction is once again involved, so you will stop quicker than if you shifted it in neutral and let it stop due to rolling friction.

Mark

Hmm, it is obvious that a sliding ball will decelerate faster than a rolling ball, since when a ball is rolling, there's almost no friction between the surface of the ball and lane.

Kind of like when you put a block of wood on the floor. No friction there whatsoever. If you think about the small area of a rolling ball's surface that's actually touching the lane, that surface of the ball is not rubbing against the lane. So there is no friction - well, there is some friction, but not nearly as much as when the surfaces are rubbing against eachother.

HOWEVER, what about the fact that the force needed to start moving a block of wood on a wooden surface is actually greater than the force needed to keep moving the block, once it's already moving (and I'm not talking about the moment of inertia here).

When an object is stationary, you need to overcome the maximum static friction (aka traction) in order to get it moving. And the coefficient of traction is usually higher than the coeff of kinetic friction (http://www.nationmaster.com/encyclopedia/Friction). Therefore, since a rolling ball and the lane don't have surfaces that move relative to each other, the coefficient of traction should apply.

When a rolling ball hits the pin, it's harder to deflect the ball, since you have to overcome traction. With a sliding ball, you (only) have to overcome friction.

Am I still wrong?

I'm just finding it really really hard to accept that a sliding ball will deflect less than a rolling ball, since I've read in multiple sources that a hooking ball is still sliding and will therefore deflect _more_.

Nevermind... you're probably right.

I found another source on the same subject and it basically says what you are saying. That the ball should hit the pin while still slipping.

The only thing that's weird is that this source says that the ball at that point is rotating faster than it is travelling? That would have to mean you're throwing the ball with like 700 or 800 rpm. !?

Your first part of the post about friction is right, I haven't included static friction in my discussion. I'm going to say why I'm having a hard time accepting this statement. When the rolling ball hits the pin towards the right, the force of static friction acts to the left to try to stop the motion, but the ball deflects to the right and then travels in the path of the deflection until it hits another pin.

When the hooking ball hits the pin, the ball is indeed still sliding, but since the revolutions of the ball are partially towards the right, part of the friction force acts to the left, which is why the ball hooks in the first place. So, if the ball is still hooking after it deflects off of a pin, it will keep on trying to hook back to the left, not just follow the path of deflection.

That's where my biggest problem with the statment lies. A ball that is purely rolling (rolling out) will just deflect without counteracting the deflection, so as it goes through the pins, it's at the mercy of them. Watching a shot roll out and just go flat is no fun and not something I ever want to see. I remember when I was younger and used to have problems with shots rolling out. I'd leave weak 10 pins all the time. Here is what I believe. A ball that is early in its hook will deflect quite a bit because its not revved up yet and made the turn it needs to make to correct for deflection. A ball that has rolled out cannot counteract deflection at all. I mentioned something like this earlier, there is a balance that needs to match your game.



I'd have to say that's a little strange. I'll see what I can find on this.

Mark

I believe that it is possible for it to end up rotating faster than it is translating. I just don't have the time to explain right now, I have to go apply some of these ideas.

Mark

Ok, here is hopefully my short explanation. It refers back to that part about the total energy being the sum of the rotational kinetic (RKE) and translational kinetic(TKE). The total energy, for the most part, stays the same with the exception of what is lost as heat from friction. Earlier in the thread, I also mentioned that a 16 lb ball that has had it's translational velocity decrease from 18 to 15 mph will lose 30.5% of it's TKE. So, with the exception of what energy is lost to friction, the revs will have to increase to balance out the loss in TKE. If the rev rate is already on the high side, the ball might have to rev up to a rotational velocity that is greater than the translational velocity to keep conservation of energy true.

Mark