# Cushions increasing ball speed

#### bud green

##### Dolley and Django
Silver Member
Players at my local pool hall seem convinced that a Diamond bar table they use increases the speed of the ball after rebounding off the cushion.

Obviously you can stun a shot with spin and make it speed up off a rail, but can a center english shot actually gain speed after contacting a rail?

I find it hard to believe...where does the extra energy come from? They seem to think the cushions can add energy. I think only transferring spin to linear movement can do this. Especially if a ball hits a rail with any kind of forward spin.

Paging Dr Dave and Mr Jewett....

#### nathandumoulin

##### WPBL / RUNOUT MEDIA
Silver Member
I've heard some pro players complain about Diamonds for this very reason. Others seem to feel that it's a positive characteristic. As for why it happens...I have no idea. Lets get someone who actually knows what they're talking about to figure out this illusion.

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#### Tramp Steamer

##### One Pocket enthusiast.
Silver Member
The same phenomenon used to be discussed regarding a baseball that was hit onto artificial turf (called Astro Turf back in the day), and then took off at a higher rate of speed.
It is an optical illusion.
When a baseball contacts the artificial turf, or an object ball contacts a rail, some of the energy of the object in motion is lost at the point of contact and the object slows. Newtonian physics proves this out. What we see is simply a different path of travel than what we are accustomed to, which is the illusion.
So there you have it. Clear as mud.

#### DogLoop

##### Doing some cueing ?
Silver Member
Object in motion, friction and imperfect elasticity ...

Players at my local pool hall seem convinced that a Diamond bar table they use increases the speed of the ball after rebounding off the cushion.

Obviously you can stun a shot with spin and make it speed up off a rail, but can a center english shot actually gain speed after contacting a rail?

I find it hard to believe...where does the extra energy come from? They seem to think the cushions can add energy. I think only transferring spin to linear movement can do this. Especially if a ball hits a rail with any kind of forward spin.

Paging Dr Dave and Mr Jewett....

If Dr Dave or Bob J chime in that would be good, but I'm sure the answer will be something like:

The rails are not adding speed to the cue ball, rather the rails are giving back more than other tables that these players are used to.
Otherwise, couldn't a player could hit a ball at medium firm speed straight up-and-down the table and watch forever while the ball never stopped, right?

#### Nostroke

##### AzB Silver Member
Silver Member
If this was really true, then 2 of these 'fast cushions' opposing each other would provide "perpetual Motion" and we know that aint happening!

#### sausage

##### Banned
Players at my local pool hall seem convinced that a Diamond bar table they use increases the speed of the ball after rebounding off the cushion.

Obviously you can stun a shot with spin and make it speed up off a rail, but can a center english shot actually gain speed after contacting a rail?

I find it hard to believe...

it's not only hard to believe, it's physically impossible. but for those who believe it, i have a perpetual motion machine that i will sell you cheap. :wink:

#### Tramp Steamer

##### One Pocket enthusiast.
Silver Member
Good answer. This is remedial level physics, something any coherent eighth grader should be able to answer.

Energy is never created or lost, it just changes form. The rubber on diamond tables may conserve more of the energy than other tables, perhaps by being cut more perfectly (i.e. if the rail hits closer to the exact center of the ball) or being a different compound of rubber.

If it were truly adding speed to a non spinning ball (wherein the spin is adding the speed by converting rotational energy to linear speed), this would be the basis for things that are proven not to exist, like perpetual motion.

dld

Excellent Double D. Well said. :thumbup2:

#### realkingcobra

##### Well-known member
Silver Member
It's impossible to speed up a ball after coming into contact with the cushions, but the cushions can rebound the ball further than you expected giving you the appearance of coming off the rail cushion faster. There are several reasons this can happen, but I'm not going to go into all the different possibility's.

Glen

#### 8pack

##### They call me 2 county !
Silver Member
It's impossible to speed up a ball after coming into contact with the cushions, but the cushions can rebound the ball further than you expected giving you the appearance of coming off the rail cushion faster. There are several reasons this can happen, but I'm not going to go into all the different possibility's.

Glen

Not only is it possible but a fact .(Maybe) Iv seen this on alot of old tables.
Im not sure if the rails are bad or whats going on.But these tables are a nightmare that just keeps getting worse.....

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#### dr_dave

##### Instructional Author
Gold Member
Silver Member
If Dr Dave or Bob J chime in that would be good, but I'm sure the answer will be something like:

The rails are not adding speed to the cue ball, rather the rails are giving back more than other tables that these players are used to.
Excellent answer! I agree.

Otherwise, couldn't a player could hit a ball at medium firm speed straight up-and-down the table and watch forever while the ball never stopped, right?
... only if the cloth were "slick" and "fast" enough.

Regards,
Dave

#### willybang

##### AzB Silver Member
Silver Member
I agree that Diamond cushions just kick the ball back more than other tables.
I played on a table recently where tha cushions killed the ball. On inspection
it showed that the cushions where too high above the centre of the ball.

##### AzB Silver Member
Silver Member
Good answer. This is remedial level physics, something any coherent eighth grader should be able to answer.

LOL, this statement alone probably addresses 50% of the general public!:grin-square:

#### SpiderWebComm

##### HelpImBeingOppressed
Silver Member
People who say that aren't educated. It's physically impossible for a ball to come off a rail faster than when it hits. The Diamond rails are just more efficient. Shows you how inefficient other rails are.

#### CreeDo

##### Fargo Rating 597
Silver Member
I think part of it is that when a ball goes into a more lively rail, it compresses the cushion more and spends a little longer dipping into the rubber before bouncing back out. For a split second, your eyes see this very brief slowdown while the rubber is compressing. Then the ball zips out of there. The change in speed from the moment of compression to the moment of exit is what gives the illusion of the ball coming in slower and somehow exiting faster.

#### 8pack

##### They call me 2 county !
Silver Member
So do some of you guys thinks its not possible a ball to come out faster
then it comes into the rail?And im not talking about a new table either.

#### dr_dave

##### Instructional Author
Gold Member
Silver Member
So do some of you guys thinks its not possible a ball to come out faster then it comes into the rail?And im not talking about a new table either.
I've tested slick vs. typical cloth conditions, for a variety of shots, and quite a lot of speed is lost in all cases. Here's a video documenting the results:

The exact amount lost will vary with cushion nose height, cloth conditions, and cushion properties, but I think the numbers in the video are typical.

Regards,
Dave

PS: BTW, the short answer to your question is: Yes ... it is not possible. Now, the CB can come out faster if it has running English or masse, but I think that is a different question.

#### SUPERSTAR

##### I am Keyser Söze
Silver Member
What about potential energy stored in the rail?

Someone needs to get a speed gun and measure the balls speed on a diamond table after a 2+ rail shot. Like shooting the ball and coming deep out of the corner 2 rails.

Until someone does do this comparison, this debate will go on forever.

#### dr_dave

##### Instructional Author
Gold Member
Silver Member
What about potential energy stored in the rail?
It can't be more than the initial kinetic energy of the ball.

Someone needs to get a speed gun and measure the balls speed on a diamond table after a 2+ rail shot. Like shooting the ball and coming deep out of the corner 2 rails.
That's a different question. Here rotational energy from running English can help speed up the ball. This can be demonstrated off one rail. A slowly moving ball with lots of running English can move away from the rail faster than it approached (i.e., it will have more translational speed, but less spin). You can easily demonstrate this by spinning a ball with your hand into a rail with lots of spin and not much forward speed.

Until someone does do this comparison, this debate will go on forever.
See:
I think this answers the main question posed in this thread, unless I am mistaken.

Regards,
Dave

#### iusedtoberich

##### AzB Silver Member
Silver Member
I understand the physics parts of it...

But from a player's perspective, certain rails are perceived to be WAY faster than others. As already stated, they do not increase the rebound speed of the ball when compared to the initial speed of the ball.

But when compared to other rails, the rebound speed can be very different.

One example of this is always brought up and that is the Diamond Table rail (intended to be this way for some reason).

A second example I'm sure most of us have seen in our travels are some Gold Crown tables where something is wrong with either the rubber, the installation, or something else, that results in even MORE speed on the rebound than the already mentioned faster Diamond tables.

In all these cases, the physics shows the rebound speed can never be greater than the initial speed. But from a practical player's standpoint, the players is expecting a certain rebound speed that has been standard forever. And now that player either plays on a Diamond with faster speed, or plays on bad rails on a GC with faster speed, and his game is completely off.

#### dr_dave

##### Instructional Author
Gold Member
Silver Member
Well stated. I agree.

Regards,
Dave

I understand the physics parts of it...

But from a player's perspective, certain rails are perceived to be WAY faster than others. As already stated, they do not increase the rebound speed of the ball when compared to the initial speed of the ball.

But when compared to other rails, the rebound speed can be very different.

One example of this is always brought up and that is the Diamond Table rail (intended to be this way for some reason).

A second example I'm sure most of us have seen in our travels are some Gold Crown tables where something is wrong with either the rubber, the installation, or something else, that results in even MORE speed on the rebound than the already mentioned faster Diamond tables.

In all these cases, the physics shows the rebound speed can never be greater than the initial speed. But from a practical player's standpoint, the players is expecting a certain rebound speed that has been standard forever. And now that player either plays on a Diamond with faster speed, or plays on bad rails on a GC with faster speed, and his game is completely off.