# Energy Transfer Question

#### Andrew Manning

##### Aspiring know-it-all
Silver Member
Directed at the scientists and engineers out there:

Controlling for tip hardness, how much variance in cue-to-ball energy transfer efficiency exists between different types of shafts?

Jump cues and break cues make it pretty obvious that certain cues will hit the ball harder given the same input from the player, but I'm wondering how much of that can be attributed to factors other than tip hardness?

Also which of those factors have the biggest effect relative to each other?

#### Bob Jewett

##### AZB Osmium Member
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Directed at the scientists and engineers out there:

Controlling for tip hardness, how much variance in cue-to-ball energy transfer efficiency exists between different types of shafts?

Jump cues and break cues make it pretty obvious that certain cues will hit the ball harder given the same input from the player, but I'm wondering how much of that can be attributed to factors other than tip hardness?

Also which of those factors have the biggest effect relative to each other?
Some shafts are not very good. By that I mean that they absorb a lot of the energy of the shot. This is easy to test by bouncing the shaft off a solid, smooth floor (tip down) and seeing how high it bounces. Dr. Dave has a video of a couple of geeks doing this.

You have to have a tip installed for this or you risk damaging the ferrule. This can be done with just the shaft, but I've only done it with a complete cue.

I think most well-built cues are more "efficient" than the tip so the tip becomes the main factor but not the only factor.

#### Andrew Manning

##### Aspiring know-it-all
Silver Member
Some shafts are not very good. By that I mean that they absorb a lot of the energy of the shot. This is easy to test by bouncing the shaft off a solid, smooth floor (tip down) and seeing how high it bounces. Dr. Dave has a video of a couple of geeks doing this.

You have to have a tip installed for this or you risk damaging the ferrule. This can be done with just the shaft, but I've only done it with a complete cue.

I think most well-built cues are more "efficient" than the tip so the tip becomes the main factor but not the only factor.

Are there known trends linking construction methods, materials, or diameter with that absorption? Does lamination vs. solid wood have much effect, or the end-drilling of LD shafts? CF vs. any of the above? Or is it less predictable than that?

#### dr_dave

##### Instructional Author
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Some shafts are not very good. By that I mean that they absorb a lot of the energy of the shot. This is easy to test by bouncing the shaft off a solid, smooth floor (tip down) and seeing how high it bounces. Dr. Dave has a video of a couple of geeks doing this.
The video, along with supporting information, can be found here:

cue efficiency resource page

I think most well-built cues are more "efficient" than the tip so the tip becomes the main factor but not the only factor.
I agree that for a typical cue with no damage and everything attached firmly, the tip is the most important (but not only) factor that dictates cue efficiency.

Regards,
Dave

#### dr_dave

##### Instructional Author
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Are there known trends linking construction methods, materials, or diameter with that absorption? Does lamination vs. solid wood have much effect, or the end-drilling of LD shafts? CF vs. any of the above? Or is it less predictable than that?
I don't know of any studies other than the limited video Bob and I did.

In general, I think a stiffer shaft and joint will result in less energy loss during the hit; but again, a soft, inelastic tip can have a big effect.

Regards,
Dave

#### mikepage

##### AzB Silver Member
Silver Member
Some shafts are not very good. By that I mean that they absorb a lot of the energy of the shot. [...]

Since you threw a value word in there...

Other than the contribution to global warming and hastening heat death of the universe, is less efficient energy transfer necessarily bad?

If you tend to play on fast cloth, there are, I think, two potential benefits of an inefficient cue.

(1) Speed/distance is a pretty sensitive function of stick speed for an efficient stick, like when your computer mouse moves too much for a small hand motion. A less efficient stick helps here, imo.

(2) If we think of "half-ball-hit and send the cueball two rails to the center of the table" as kind of the breadbox of stroke speed, then on fast cloth, this go-to stroke may occur at a stroke speed slower than the peak of the comfort/accuracy curve.

#### Bob Jewett

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I don't know of any studies other than the limited video Bob and I did. ...
I was told a long time ago that Predator did tests of efficiency of shafts/tips using their robot, Iron Willie. I think that was primarily aimed at developing break cues. I don't know what tests they've done recently, but some qualitative results are at https://www.predatorcues.com/shafts/predator-low-deflection-shaft/ for energy transfer.

An earlier test was done by A.D. Moore, an engineering professor at the University of Michigan, in 1941. He hit a ball with a cue stick in a setup where both were hanging on wires. The height the ball swung up compared to the height the cue stick started at gave the efficiency of the hit (he calls it the coefficient of restitution) after some calculation. From Moore's manuscript:

... At any rate, the writer experimentally determined e for the case
in hand. The set-up was made and the readings were taken in one
afternoon (11-25-1941). The simplicity of the set-up, the ease of
making observations, and the accuracy secured indicate that someone
could, without much effort, add greatly to our list of coefficients.
The cue and ivory ball were hung by light steel wires beneath a
horizontal 10-inch board. String was wrapped around the ball, and
held in place with Scotch tape. Loops in the string permitted two
wires to be attached. The wires went to screw-eyes put in the edges
of the board, across from each other. Similar pairs of wires (two
pairs) suspended the cue for direct central impact, The vertical
radii were all 20 inches. When both bodies were at rest, they grazingly
touched.
The writer's brass-jointed cue was used. Its length is 57.5
inches ...
The result was that Moore measured a value of e of 0.81 or 81% for his equipment.

Moore's experiment suggests a somewhat more controlled test than the one Dave and I did. Suspend a stick as Moore describes but have it hit a very heavy smooth object (block of iron? concrete wall?) and see how far it swings back. The target does not have to be a ball to get a good measurement.

#### Bob Jewett

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Since you threw a value word in there...

Other than the contribution to global warming and hastening heat death of the universe, is less efficient energy transfer necessarily bad?

If you tend to play on fast cloth, there are, I think, two potential benefits of an inefficient cue.

(1) Speed/distance is a pretty sensitive function of stick speed for an efficient stick, like when your computer mouse moves too much for a small hand motion. A less efficient stick helps here, imo.

(2) If we think of "half-ball-hit and send the cueball two rails to the center of the table" as kind of the breadbox of stroke speed, then on fast cloth, this go-to stroke may occur at a stroke speed slower than the peak of the comfort/accuracy curve.
I think the efficiencies are all well over 50%. Going from 87% to 75% (as a semi-reasonable example) doesn't seem like it would move much on the hand speed comfort curve.

One problem with having an "inefficient" cue is that during contact the cue stick does not slow down as much and the cue ball does not speed up as much as for a more efficient stick. For a center-ball hit, you can just crank up your hand speed to get to the same final ball speed.

However, if you hit well off-center with an inefficient tip/shaft you risk having the cue stick never slow down to the below the final speed of the cue ball. The results for such a shot are not well defined.:smile:

How about just changing to a lighter stick for faster cloth? That will also help to slow the cue more to avoid dragging on the ball for extreme spin shots.

#### dr_dave

##### Instructional Author
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I think the efficiencies are all well over 50%. Going from 87% to 75% (as a semi-reasonable example) doesn't seem like it would move much on the hand speed comfort curve.

One problem with having an "inefficient" cue is that during contact the cue stick does not slow down as much and the cue ball does not speed up as much as for a more efficient stick. For a center-ball hit, you can just crank up your hand speed to get to the same final ball speed.

However, if you hit well off-center with an inefficient tip/shaft you risk having the cue stick never slow down to the below the final speed of the cue ball. The results for such a shot are not well defined.:smile:

How about just changing to a lighter stick for faster cloth? That will also help to slow the cue more to avoid dragging on the ball for extreme spin shots.
For those interested in the effects of tip efficiency and cue weight on the likelyhood of bad hits at large tip offsets, see:

TP A.30 - The effects of cue tip offset, cue weight, and cue speed on cue ball speed and spin

I like the idea of using a lighter cue on faster cloth.

Enjoy,
Dave

PS: If you don't like the math and physics, you can just look at the plots and conclusion statements.

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