check out my new posting regarding feather & nylon at....

http://www.badmintonforum.com/forums/read.php?f=2&i=23694&t=23618

You claimed that I had previously made some erroneous assertions regarding nylon shuttle, but you never said what they were. Let's hear your thoughts.

The cooler post in question is at...

http://www.badmintonforum.com/forums/read.php?f=2&i=19906&t=19728

Keeping my words, i will try to pass on my thoughts. I am not asserting that my knowledge is 100% correct as there isn't 100% certainty in science. However, it is no revelation either as simple high school physics's principles are suffice and shoudln't require Phd person to understand it.

In that post, u had made some correct and not so correct description of feather vs nylon shuttles. I will only highlights the one i feel that are not correct.

gregr: "However, even nylon shuttles with real cork bases still don't sound quite as crisp & clean as their feather counterparts. I suspect that the difference in sound is due, in large part, to the initial speed of the shuttle coming off the racket. It seems to me that the feather shuttle comes off the racket at a faster velocity than most nylon shuttles" "Many synthetic shuttles are, what I call, "constant velocity" birds. Altho' they may not come off the racket quite as fast as a feather bird, ..."

cooler: Assuming constant racket angular velocity on a hard smash stroke from similar rackets, both corked nylon (n) and feather shuttle (f) will exit the racket at similar velocities (V). Since no one had conducted this experiment b4 of comparing exit Vn vs Vf, i would in this case consider any difference in V , if it even detectable by the best measuring devices, as insignificantly small and equates exit both Vn and Vf as being equal. You may now say "cooler, u r making an assumption here as there have not any test or experiment done to support your claim" True, however, mother nature is pretty consistent on basic principles and i have derive my claim here from fluid mechanics, and mechanic dynamics principles. (Maybe this is why no test or experiments were done as it is not a mystery or an unknown variable) This is not rocket science. Vf and Vn do differ after they leave the racket. However, the sound is created at contact and subsequence delta V after leaving the racket has no role to play in contact sound. . Therefore, the difference of sound is not due to the difference of exit V and there is no difference in exit V either. Please note that this is a VERY brief explaination and i had constrained this explaination on hard smash strokes only. Also, i've made no attempt to explain why they differ in sound on contact.

Other incorrect statements of your IMO are:

1. "The primary reason a hard hit feather shuttle comes off the racket quickly but also has more braking action is that the feathers collapse more than the nylon skirt does at impact"

2. "A difference in spin characteristics could also account for differences in deceleration & initial speed between a feather shuttle & a synthetic shuttle. More speculation... could it be that the feather shuttle has little or no spin initially (at impact) whereas the synthetic shuttle starts to spin sooner? This could possibly be another factor."

3. "Another possibility is to track down James or Jon Poole for more info. I don't know is James Poole is still alive but he is undoubtedly retired. Last I heard Jon R. Poole was an assistant professor in the Dept. of Teaching & Learning at Virginia Polytechnic Institute and State University (where he also received his doctorate)."

I'm not doubting nor discrediting J. Poole credential(s) or his educational background but what does he teaches and what kind of Phd degree he got?

I will not attempt to explain item #1 and #2 as it would require me to first explain numerous fluid mechanics, statics and dynamics mechanics, material science principles before i can even begin to dwell into the differences of nylon vs feather dynamics on and off the racquet.

I hope that i didn't come across as being arrogant but i dislike typing long english composition to explain mathematical and scientific principles without the aide of equations and symbols. You definitely does a better job than me in explaining things in linguistic way as i have enjoyed your previous explaination of pronation, smashing technique & positioning very much.

Cooler, your assumptions are overlooking some important points. The physics involved is more complex than you think (I'm sure that it is more complex than I can fathom either). Remember the difference between elastic and non-elastice collisions? The transfer will not always be the same even IF the masses (of the shuttles) involved are similar. Other factors are involved. Some energy is lost thru the heat of compression; this can very well be different if the cork material differs or if the masses of the 2 types of shuttles are somewhat different. There is also a matter of DWELL... how long (milliseconds) does shuttle "cork" stay on the strings? The material type & its compression characteristics have some bearing on dwell.

Air resistance is a MAJOR factor in determining how fast the shuttle comes off the racket. The feather shuttle becomes more streamlined as it leaves the racket on a hard hit, thus offering less air resistance... initial speed would be greater in this case. Mag, I think, pointed out that high speed studies have shown that skirt of the nylon shuttle distorts in a very different manner... in such a way that air resistance is actually greater for a very short time. This results in a slower initial speed.

The shuttle is now in your court...

Are you disputing that the feathers become more streamlined as they come off the racket on a hard hit shot? High speed studies have indicated that this happens. If you accept that, would you agree that a streamlined bird would have less air resistance and that with less air resitance the shuttle would not lose it speed as rapidly? Wouldn't you also agree that the feathers would tend to regain their origianl shape and would thus have greater air resitance as it continued to travel? Would this not result in a greater braking action?

High speed studies also show that nylon shuttles do not experinece the same streamlining action that feather do. In fact, their skirt distorts on impact so that the "hit" is not as "clean". I would guess that this type of distortion causes more air turbulence than the streamlined feather shuttle.

I'm not going to defend point #2. As i indicated b4, it was pure speculation on my part in attempt to propose another possible diff in flight characteristics between feather & nylon. I will say, however, that I do believe that the spin characteristics differ. For one thing, as a lefty I can impart more spin on a feather shuttle with a sliced FH overhead shot than a right handed player. This happens cuz of the way the feather overlap. when I cut the bird, I'm going against the overlap which grabs the tips of the shuttle feathers moreso than when a righty cuts the bird. I don't have this advantage with a nylon shuttle. I have noticed differences in spin (nylon vs feather) in other situations as well. When I perform a net drop, the nylon shuttle tumbles in a different manner than the feather bird.

James Poole was the last of the U.S. international champions (way back in the 1960s). He is considered one of the greatest badminton champs of all times. The refernences that I've seen regarding his scientific work has been with biomechanics and physiology; much of it with badminton. I don't really know for certain what his areas of expertise are. Check out the following...

A scientific paper on the IBF site makes reference to Dr. Poole:
http://www.intbadfed.org/review.htm#BIOMECHANICS

Also check out this back page from his book on badminton:
http://www.amazon.com/exec/obidos/tg/stores/detail/-/books/0881338923/reader/8/ref=lib_dp_TBCV/102-8121056-8048158#reader-link

It could be that the crisp sound of a feather shuttle smash or clear is not only the contact itself but possibly ALSO the sound created at the bird first leaves the strings. I may be wrong about this, but I do believe that the impact and the resulting actions after impact are very complex; (much as the The Big Bang and the first few fractions of a second after the Bang were so incredibly complex that it violated the laws of physics as they exist now).

A lot of the perceived diffs in speed might actually happen when the shuttle has left the strings and is only a few centimeters away from it. I believe, at this point, the feather shuttle will be faster than most nylon shuttles due to the diffs in skirt/feather distortion & diffs in air resistance. I suspect that the feather shuttle also turns around faster than the nylon shuttle when it leaves the stringbed. This also could be attributed to the difference in distortion of the skirt vs the feathers. The diff in the cork/feather balance of the shuttles may also be a factor in the turn-around time. If the nylon shuttle doesn't turn around quite as fast (as i suggest) it would catch more air (yet, even more air resistance).

When I speak of the initial speed of the shuttle, I am referrring to fist few cm of travel as it leaves the stringbed. Does it accelerate in those first milliseconds? I would be tempted to think so if we assume that momentum is conserved. For an instant, the shuttle and racket strings at the contact point are traveling at the same speed. As the shuttle leave the strings the colliding masses become seperated. It seems that the racket does not decelerate significantly immediately after impact from its contact velocity, yet the shuttle moves away from the strings (cuz it is moving faster than the racket!). This acceleration of the shuttle happens as a result of the collision with momentum preserved. The cork/rubber regains its original shape & the stringbed which has stored some of the energ of the impact throws the shuttle out.

Am I wrong about acceleration of the shuttle as it leave the strings? At one instant it is traveling at the same speed as the racket and the next instant it is traveling faster. IF (not the caps) the racket does not lose a significant amt of speed from its racket+shuttle speed, then the shuttle must acclerate immediately after leaving the stringbed. If I'm correct about this then it is reasonable to assume that the feather shuttle & the nylon shuttle do not acclerate quite the same due to a variety of other factors (such as distortion, turn-around time, air resistance, etc).

However, as the shuttle travels a few meters away than things change 'cuz the aerodynamics of the nylon is somewhat different than the feather. I believe the added braking action of the feathers (as they regain their wider position) is one reason. Other differnences in construction account for diffs in aerodynamics as well.

It should be noted that there are differnces from one feather shuttle model to the next. However, there are more variances in differerent models of nylon shuttles (some approximate feather characteristics much better than others).

i have read J. Poole's paper on biomechanics of badminton. It seem the paper dealt strictly in the area of body mechanics and energy transfer to the racket. What i have been debating with u here deal with the interaction of shuttle and string, with makeup of racket and player being a constant. Do u remember your original post talking about the difference in sound between feather and nylon shuttles?

That's why i didn't talk about shuttles velocity profile AFTER exiting the string. It is a no brainer that Vf and Vn are different in it flight path. Anybody can notice that obvious difference.

i merely mentioned the paper on the IBF site to indicate that he had considerable credibility with the international badminton community. that topic of that particular paper had nothing to do with our present discussion.

The differences in flight characteristics may be noticeably different some time after the shuttle has left the racket, but what is not so obvious is what transpires at contact & IMMEDIATELY after contact. This short period of time has been the focus of my comments. While the bird is ON the strings, they are (obviously) both traveling at the same speed. However, what happens AS the shuttles leaves the racket differs significantly as I see it; other differences come into play as the shuttle continues on. Are we agreed on that?

sure, i can agreed on those points. It's good that u agreed that exit Vf = Vn
"While the bird is ON the strings, they are (obviously) both traveling at the same speed. "


however, that is what i'm trying to say. If i may reiterate,

Vf=Vn at contact as we agreed
feather and nylon shuttle make different sound at contact duration
therefore, difference in sound of feather & nylon shuttles is not function of exit Vf or Vn

sure, i can agreed on those points. It's good that u agreed that exit Vf = Vn
"While the bird is ON the strings, they are (obviously) both traveling at the same speed. "


however, that is what i'm trying to say. If i may reiterate,

Vf=Vn at contact as we agreed
feather and nylon shuttle make different sound at contact duration
therefore, difference in sound of feather & nylon shuttles is not function of exit Vf or Vn

As we both recognize the intricacy details of shuttle impact sound and flight, it is the reason why i had been exclusively talking about V of shuttles in relation to impact sound and not entered into discussion of its flight path. However, you seem to wander off into detail of shuttle flight comparision which makes it hard for me to focus my point of view regarding relationship of impact sound to shuttle exit velocities.

Since there is enough variables just involving the impact sound versus shuttle V topic, i even had predefine my explaination. **cooler: Assuming constant racket angular velocity on a hard smash stroke from similar rackets, both corked nylon (n) and feather shuttle (f) ** When i say similar rackets i also meant same strings with same tension. Also, i should have also said n and f shuttles are brand new and of similar weight too. (I also assume that the nylon and feather shuttles comparion made here are from the same maker, ex. yonex Mavis versus Aerosensa which i have to assume yonex bought the cork from the same supplier, hopefully harvested from the same tree forest or farm). If any of the above condition differs, there is no way one could condense the topic specifically about impact sound versus n and f shuttles. Since i was talking about corked shuttles, your points about cork material, cork compression and heat lost are quite irrelevant as both corks of the n and f shuttles would experience similar distortion as well. If the n and f cork is made from the same material and each shuttle is similar in weight, the dwell time would be similar as well.

Of course the ambient air resistance would dominate after the shuttles exit the racket string but that is beside the point. Who would argue with this point anyway?

Yes, the shuttle is on my side of the court but IMO it flew out of bound. Sorry, a point for me :)

It's true that shuttle dynamics is complex but it can be described by widely accepted newtionian physics. Although the big band is much much more complex, scientists have able to understand it down to around t=10**-20 second which is not bad imo.

It is also true acceleration after leaving the string bed also differs between different shuttles but imo have unmeasureable or no relationship to the impact sound, assuming that we are talking about in hard smashes.

.

sorry guys, it's late. I hope kwun new software has a time delay feature (few minutes?) that allow re-editing.

Actually, the original post (from early Nov) that set off this lively discussion had very little to do with the sound of the shuttle. It was all about the phyics & aerodynamics of feather vs nylon. In a later thread (Nov/Dec), you had made the statement that you disagreed with a # of the assertions that I had made but you did not elaborate at that time.

In this thread, it seems that you have several points of contention. However, it seems that your primary focus now is the sound & the velocity at the instant of impact. Altho' I had made some statements about the instant of impact, one of my primary foci was the velocity of the shuttle just after impact rather than its velocity right at impact. Perhaps, this is were our discussion was out of sync.

Actually, this is the very type of discussion I was looking for back in Nov, but somehow the thread got sIdetracked on something about replaceable feathers or something else only remotely related.

I'll have to come back to visit some of the other issues you present here when I've got more time to read & digest it. Keep it coming.

actually what I was saying is that Vracket = Vshuttle at impact. Vf may very well be the same as Vn right at impact, but I am thinking that DWELL time and the velocites immediately after impact are more important. When I was speaking of the "initial" velocity in my Nov & subsequent post I was referring to the speed just after impact.

Perhaps, the initial velocity of which I speak may or may not have anything to do with the sound. You assume only the contact contributes to the sound. I'm suggesting that perhaps the way a feather shuttle "pops" off the stringbed has something to do with the sound. This could include the nature of the contact itself, the cork/rubber material involved, the dwell time AND the speed (or acceleration?) of the shuttle immediately AFTER contact.

Your "exit V" and my intial V may not be exactly the same thing. I am thinking that the shuttle might very well accelerate for a brief time just after contact so that Vmax is perhaps somehwat greater than your Vexit. I can't say for sure that this Vmax contributes to the sound we hear, but it may, in fact, do so. I'm am saying that I believe that Vmax for feather is faster than Vmax for nylon.

well this sounds a bit different. we are agreed that the acceleration after contact differs but we are not in accord on weather or not this post-contact acceleration has any bearing on the sound. You may be correct, but I'm thinking that a shuttle that is rapidly accelerating to 150 to 200+ MPH may very well add to the acoustic energy released as a result of the contact itself.

We can also agree that, altho' the racket-shuttle-air interaction is very complex, it doesn't REALLY compare to the complexity of the Big Bang (this was just an exaggerated simile).

Above, I had suggested that the air rushing past a shuttle accelerating & achieveing speeds in excess of 150 MPH would contribute to the sound of the impact that we perceive. Mayhaps, what may be an even larger factor in the generation of acoustic energy is the amount of turbulence created as the shuttle is leaving the racket. IF a feather shuttle becomes more streamlined at/after contact and the nylon bird distorts more irregularly AND the turn-around time of the nylon is greater than that of feather, then it would stand to reason that the nylon shuttle creates more air turbulence. These factors would not only affect Vmax but it could possibly have a profound effect on the sound we hear.

waddayathink?

as if things weren't complex enough.......

Let me see
Assuming the shuttle is causing the sound......

But what if the shuttle doesn't contribute much to the sound. Maybe it's the strings. and the different quality of sound is due to a different material on the string i.e. nylon vs feather.

Here is a "low velocity" example:
bang your racquet against your stationary knee with the strings
1) a light impact causes a small sound - the knee doesn't move
2) a harder impact causes a louder sound - the knee doesn't move

Now bang the racquet against the heel of the hand

Result: a different quality of sound! Could it be the strings causing the sound?

OK, I'm not going to get embroiled with physics but just suggesting an alternate hypothesis.

cheung, i'm pleasantly surprised. You have pinpointed the main source of impact sound from a hard smash, whether on a nylon or feather shuttles. In my previous postings, i was mainly focusing on the delinking of the impact sound difference to difference exit V. IMO, 90%+ of the impact sound energy that one hear is emitted from string vibration. On softer strokes, IMO, 95%+ of the sound come from the string. This further support that velocity difference at impact, if any, doesn't explain the difference in impact sound of a nylon versus feather shuttle which i have been repeatedly trying to say. As cheung had mentioned here, and Mag had mentioned back in the Nov/01 post, it is the skirt material difference of nylon versus feather shuttles that determine their unique impact sound.

gregr, as we both agreed, descripting all the mechancis of a shuttle path from racquet to rest state (V=0) is quite comprehensive. It is the reason why i have restricted my explaination to just one topic: impact sound vs exit velocity differences of nylon versus feather shuttles. As you have seen, after more than 3 threads and many posting, i have yet convince you that difference in Vn and Vf, if any, under hard smashes do not determine the sound their impact sound differences. As the is topic is still hung, why go talk about the shuttle physics after leaving the racquet or shuttle spins or shuttle balance or shuttle deformation. As you have stateed before, your original post got side tracked because no one else had stay in topic and none of your inquiries got debated nor answered back in nov, 2001.(except for Mag)