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dr_dave
01-15-2008, 12:06 AM
Below is an e-mail question I received recently, along with my reply. I wanted to share it with you guys for comment and discussion. I've heard about this experiment from several people. If you haven't tried it yet, give it a try. The visual results are very interesting.

<blockquote><font class="small">Quote e-mail question:</font><hr>What you may find interesting would be to place a striped ball with the stripe tilted as the ball is at 0:18 in your NV B.7 (http://billiards.colostate.edu/normal_videos/new/NVB-7.htm) video. Instead of hitting it with sidespin only, also hit it with some draw. Hit it low, off center and on the stripe. It would be like you are back spinning the ball so it keeps the stripe in line spinning in reverse on a tilted axis as it goes down the table. ( the stripe aligned with the spin direction)

The ball should come up to a vertical spin (perpendicular to the table) and then keep rolling. It does... but not how you would think. The ball comes up to a vertical spin and the axis then actually flips over 90 degrees from the original axis that it started on. You can't see that with a measels ball.

If you put arrows on the starting spin direction and stop the ball in towels or use something to catch the ball on the opposite end of the table... the arrows will be facing in the complete opposite direction. That is why I mentioned the red/white ball. If the red side starts out facing one side of the table it will flip over and the red side will face the opposite direction. A complete ball flip or turn over.<hr /></blockquote>The reason why you can't see it with the measles ball is the spin axis really isn't flipping. It just looks that way because of how the 2-color or striped ball rotates sideways and forward as the drag converts to roll.

I have tried this experiment several times with a striped ball, a 2-color Elephant Practice Ball, and an Aramith "measles" ball. The experiment doesn't change my understanding. When you hit the ball with bottom-left English, the spin axis starts off pointing down and to the right. If you use your right hand and curl your fingers in the spin direction, your thumb will point in the spin axis direction. With just left spin, your thumb would point straight down, with your fingers curling in the clockwise direction (looking from above). With just forward roll and no sidespin, your thumb would point to the left, with your fingers curling in the forward roll direction. Now, with the shot in question, this is how the spin axis changes:

1.) The thumb (spin axis) first points down and to the left (at 4:30 o'clock), with the bottom-left spin.

2.) After the drag removes the bottom spin, only left idespin remains for a moment, and the thumb points straight down (6:00 o'clock).

3.) As forward roll starts develops, the spin axis drifts towards the left (towards 7:30 o'clock), as the ball now has forward roll and the left sidespin.

The spin axis does not flip. It gradually drifts through steps 1, 2, and 3. Again, the 2-color Elephant Practice Ball or a striped ball kind of creates a visual illusion (leading to your "flip" interpretation). It looks cool, but I don't think it is showing what you think it is showing. Try it with an Aramith measles ball, and the spin-axis changes described above are fairly easy to see. The measles don't lie.

Regards,
Dave

Billy_Bob
01-15-2008, 11:42 AM
I just tried this using a striped ball as the cue ball for the "Hook Shot" from 99 critical shots.

It works like magic!

In the past I have had trouble showing people this shot and explaining what is going on with the cue ball. This will help a lot!

The stripe switches after contacting the rail to point toward the "A" on the below diagram. So first the vertical stripe is pointing at the 3 ball, then after contacting the rail, the rail redirects the ball to have a forward motion toward "A". Thus the "curving effect shown.

Here is a diagram of the hook shot...

http://CueTable.com/P/?@2CanU2OBRn3QXIY2WanU2Wcbo2WaOo2WYhl2WXre2WXSV3WX QY3WWbY2jBRn2jbMW@

With the hook shot shown, the 15 striped ball is the cue ball. Align the stripe on the ball vertical going straight toward the 3 ball. Shoot the 3 ball into the side with a slight left cut (hit slightly to the right side of the 3 ball). Shoot high center, use a MEDIUM speed stroke with TONS of follow through. So much follow through, you are trying to send the tip of your cue through the far wall!

Fast stroke does not work. Also alignment of the cue ball is critical. Somewhere near the spot and resting toward the corner pocket a few inches (on my 7 ft. table.)

The cue ball needs to have a LOT of follow at the time it hits the 3 ball to get this shot to work.

dr_dave
01-15-2008, 02:32 PM
Billy_Bob,

Thank you for sharing this. Again, I think an "measles" ball helps you visualize the actual spin a little better, especially if you have a camera for slower playback.

Regards,
Dave
<blockquote><font class="small">Quote Billy_Bob:</font><hr> I just tried this using a striped ball as the cue ball for the "Hook Shot" from 99 critical shots.

It works like magic!

In the past I have had trouble showing people this shot and explaining what is going on with the cue ball. This will help a lot!

The stripe switches after contacting the rail to point toward the "A" on the below diagram. So first the vertical stripe is pointing at the 3 ball, then after contacting the rail, the rail redirects the ball to have a forward motion toward "A". Thus the "curving effect shown.

Here is a diagram of the hook shot...

http://CueTable.com/P/?@2CanU2OBRn3QXIY2WanU2Wcbo2WaOo2WYhl2WXre2WXSV3WX QY3WWbY2jBRn2jbMW@

With the hook shot shown, the 15 striped ball is the cue ball. Align the stripe on the ball vertical going straight toward the 3 ball. Shoot the 3 ball into the side with a slight left cut (hit slightly to the right side of the 3 ball). Shoot high center, use a MEDIUM speed stroke with TONS of follow through. So much follow through, you are trying to send the tip of your cue through the far wall!

Fast stroke does not work. Also alignment of the cue ball is critical. Somewhere near the spot and resting toward the corner pocket a few inches (on my 7 ft. table.)

The cue ball needs to have a LOT of follow at the time it hits the 3 ball to get this shot to work.
<hr /></blockquote>

dr_dave
02-04-2008, 04:15 PM
FYI, I just posted a video that demonstrates and explains (with the help of high-speed video) how the spin axis changes as drag converts bottom spin to forward roll, while English persists. Here it is:

NV B.10 - Drag spin loss and English persistence (http://billiards.colostate.edu/normal_videos/new/NVB-10.htm)

If you not able to view YouTube videos, an alternative (lower quality) version can be viewed here (http://billiards.colostate.edu/normal_videos/index_alt.html).

Check it out and give it a try. It's a cool visual demo.

Regards,
Dave

wolfdancer
02-04-2008, 05:03 PM
I believe Buddy Hall shows this shot in his position play Video....now all I need is buddy's stroke, to make it work. Just watched a great action shot by Larry Nevel on Youtube
Nevel Vs Schmidt, with an unfortunate scratch at the end.
shows up at the 4.25 min mark on the match:

Larry's break form:

Ralph_Kramden
02-04-2008, 06:44 PM
<blockquote><font class="small">Quote dr_dave:</font><hr> FYI, I just posted a video that demonstrates and explains (with the help of high-speed video) how the spin axis changes as drag converts bottom spin to forward roll, while English persists. Here it is:

NV B.10 - Drag spin loss and English persistence (http://billiards.colostate.edu/normal_videos/new/NVB-10.htm)

If you not able to view YouTube videos, an alternative (lower quality) version can be viewed here (http://billiards.colostate.edu/normal_videos/index_alt.html).

Check it out and give it a try. It's a cool visual demo.

Regards,
Dave <hr /></blockquote>

Very good demo. It shows the importance of a center ball hit on a longer drawshot. Thanks for the video.

dr_dave
02-05-2008, 10:03 AM
<blockquote><font class="small">Quote Ralph_Kramden:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> FYI, I just posted a video that demonstrates and explains (with the help of high-speed video) how the spin axis changes as drag converts bottom spin to forward roll, while English persists. Here it is:

NV B.10 - Drag spin loss and English persistence (http://billiards.colostate.edu/normal_videos/new/NVB-10.htm)

If you not able to view YouTube videos, an alternative (lower quality) version can be viewed here (http://billiards.colostate.edu/normal_videos/index_alt.html).

Check it out and give it a try. It's a cool visual demo.

Regards,
Dave<hr /></blockquote>

Very good demo. It shows the importance of a center ball hit on a longer drawshot. Thanks for the video.<hr /></blockquote>I'm not sure what you mean by this, but I'm glad you like the video.

Dave

Ralph_Kramden
02-05-2008, 10:37 AM
<blockquote><font class="small">Quote Ralph_Kramden:</font><hr>
Very good demo. It shows the importance of a center ball hit on a longer drawshot. Thanks for the video.<blockquote><font class="small">Quote dr_dave:</font><hr>I'm not sure what you mean by this, but I'm glad you like the video.
<hr /></blockquote>

What I meant was that people who hit long draws with an off center tip may be contacting the OB when the CB is actually spinning horizontaly, although they may think it is still spinning backwards.

dr_dave
02-05-2008, 10:45 AM
<blockquote><font class="small">Quote Ralph_Kramden:</font><hr>Very good demo. It shows the importance of a center ball hit on a longer drawshot. Thanks for the video.<blockquote><font class="small">Quote dr_dave:</font><hr>I'm not sure what you mean by this, but I'm glad you like the video.<hr /></blockquote>What I meant was that people who hit long draws with an off center tip may be contacting the OB when the CB is actually spinning horizontaly, although they may think it is still spinning backwards.<hr /></blockquote>Good point. A below center hit doesn't always result in "draw." Also, stun with sidespin can result in more throw (collision-induced or spin-induced, depending on the type of spin: outside or inside English). The slower speed resulting from the drag action can also increase the amount of throw. FYI, all of these effects (and more) are covered in my throw article series (http://billiards.colostate.edu/bd_articles/index.html).

Regards,
Dave

wolfdancer
02-07-2008, 09:22 PM
web page (http://www.moviewavs.com/php/sounds/?id=gog&amp;media=MP3S&amp;type=Movies&amp;movie=Score&amp;quote=p hysics.txt&amp;file=physics.mp3)