Serve toss question....

[uspta146749877]

I do NOT have a book by Plagenhoef

It looks to me like Plagenhoef assigned a speed of 102mph to the entire path of his theoretical serve. I assigned a final speed at court contact of 90mph for a 120mph serve and assumed deceleration was constant to arrive at an average speed of 105mph. But I broke the problem down to address the fact that there are two tasks inherent in getting the serve in the box. First, it has to get over the net and it is going faster that first 39plus feet as it drops to its window of acceptance. Second, it has to land in front of the service line. For the first part we are worried about not dropping too low in the net, but for the second part we are worried about staying too high and landing beyond the service line.

In fact, because of wind resistance and drag increasing with the square of the velocity, the ball probably slows down quicker as it approaches the net than it does past the net when it is going slower. Therefore, 102mph may be the truer number.

don

I do NOT know whether your first sentence is true or NOT

[uspta146749877]

10 degrees

If 7.5 degrees got me about 60 inches of drop, then that is about 8 inches per degree. The very top of the net would be almost 8 degrees down. The only way you could go up to 9 or 10 degrees would be if your contact point was higher or the speed of your serve was much higher. Remember a little faster serve will have a disproportionately greater reduction in drop due to gravity because gravity is an accelerating force and if you speed the ball up 20%, the amount of time the ball drops may be reduced by 1/6th, but the amount the ball drops due to gravity in that time will be reduced by much more than 1/6th because the time you are taking off is the time when the ball is dropping the fastest in that part of its journey. Still it seems to me spin and wind resistance will only make the ball drop faster and to get to those 9 or 10 degree numbers (for a fast ball), the contact point will have to be more like 10 feet instead of 9.5 feet. That would seem to be reasonable to me, until we start to consider the lean into the court. But that should balance out. We won't know until we actually do the cranking. Anybody else want to try?

don

It is NOT obvious whether a ball up at a beginning would allow us to get to 10 degrees LATER.I have some problems trying to produce any kind of drawing here.
Let me use a name of a ballistic curve here.
It is possible that a ballistic curve with a max 4 feet inside
would be the same as a toss 4 feet inside

An example of a ballistic curve is shown in a link below

http://www.google.com/imgres?imgurl=http://www.whitemuzzleloading.com/myweb2/images/whiterifles/best_l5.gif&imgrefurl=http://www.whitemuzzleloading.com/myweb2/images/whiterifles/best_loads_in_white_rifles.htm&h=230&w=400&sz=21&tbnid=MJYhbmEbk_ziHM:&tbnh=71&tbnw=124&prev=/images%3Fq%3D%2522ballistic%2Bcurve%2522&zoom=1&q=%22ballistic+curve%22&hl=en&usg=__13C9T8XMYnApe1Lq1kCDw6HeRPM=&sa=X&ei=aOcXTaTbHcK78gaL3PCZDg&sqi=2&ved=0CCcQ9QEwAQ

If one of you are able to put a ballistic curve EXPLICITLY in a post I can make some extra useful drawing
PS I want a 7 feet high kick as well.

[tennis_chiro]

2 degrees less

I do NOT understand a sentence
"Of course, I need to redo the calculations for a ball that starts out on a course with a slope of 2 degrees less than that. "

What I mean is, if my calculations were for 7.5 degrees at 3" above the net and there is an acceptance window of 2 to 3 degrees, it can't be 2 degrees lower (9.5), that would definitely be in the net, but perhaps it could be 2 degrees higher (although I doubt it initially) at 5.5 degrees. I need to redo the spread sheet for that.

I will do that after I make the sweet potatoes and lima beans to go with the turkey breast I just cooked today because I was giving lessons yesterday afternoon!
don

[uspta146749877]

Ad hoc constants

There are some ad hoc constants in your spreadsheet.

One of them is in a formula for an average speed= ...

Probably:
1.it would be good to explain how you arrived to this formula.
I can make some guesses but I do NOT see any reason to make your life easier

2.it would be good to see whether Plagenhoef had a similar assumption-my guess is : no

[uspta146749877]

A possible summary?

One of us should provide a post in a form of a post-
what was done and what should be done

[uspta146749877]

A related remark

Clearly, these are great illustrations and much nicer than the clumsy attempts I have posted in earlier posts. But they are just that, illustrations. To make a quantitative comparison, we would need the point tracker illustration for Soderling on a 130 mph serve and the same shot from someone like Krajicek who reaches at least the full 4 plus feet into the court. Then you would need to overlay those two images and you could see the advantage/disadvantage of the forward toss. I think PointTracker might even have the actual data potential in their statistics to pull out net clearance, etc. Perhaps we will get that on our digital feeds 5 or 10 years from now. There is already quite a bit on the ATP livestreaming TennisTV for live matches.

But I don't see anything in these illustrations that allows us to make a quantitative comparison of the advantage/disadvantage of

1. jumping up to hit the serve
2. tossing forward further into the court (and the reduction is reaction time, especially usable reaction time [my "action time"])
3. standing in different positions to increase the "acceptance window" of Brody (and the relationship changing the reaction time has because the server is a little further away from the receiver
4. (and I haven't seen anyone address this)while clearly, Sampras's serve was distinctive by the tremendous spin he had on his serve, how much does the spin of the ball actually slow the ball down by increasing the drag, even as it puts more balls in the court by bringing them down quicker. (Golf spends tens of millions of dollars on technology to improve dimple design to reduce spin on the drive while maintaining it on iron shots, but the bottom line is the longer hitting pros have a much lower rate of spin on their drives.)

I'm looking for what is the real benefit of getting forward on the toss. I don't think it should be emphasized until the player has the motion under control. But once that is achieved, how much benefit is really garnered by tossing the ball out into the court. I don't think you gain that much in raw MPHs, but taking away 4 feet of a "40 foot action distance" is a significant advantage for the server. How much faster is that ball when it hits the court and loses up to a third of its MPHs on the surface of the court than the ball (like Soderling's) which is hit from almost 4 feet further back. I think part of the reason for the low first serve percentage in today's game (relative to great servers of the past like Gonzales) is the blind emphasis on speed and the belief that vertical leg drive provides the difference between 115mph and 135mph serves. I think it probably provides 5 mph at most, but ends up cutting down average first serve percentages by 10 to 20% (and more among less accomplished players). I have no real data on that; just my own feelings and observations.

Invariably, the students I coach serve better when I first make them stand still and hit up at the ball in balance. Once they have MASTERED that skill, then I want them falling into the court on a somewhat forward toss, driving up with their legs and reaching up to the ball. But only after they have MASTERED that do I want them to start flinging themselves into the galaxy. Otherwise, they invariably end up hitting a little under the ball and having a great deal of difficulty getting the ball in the service box. But in participating in this thread, I am more open if not actually convinced, that the eventual and final goal for service development has to be the forward toss like Krajicek if not the actual Brian Battistone. Give me a Blake Griffin at 10 and let me train him for 5 or 6 years and if he has a complete game and Griffin's athleticsm...serving and volleying meeting the ball almost 8 or 9 feet into the court and cutting the receiver's "action distance" down from 40 feet to a little over 30 feet...not to mention the angles he could create...I think they would almost certainly change the rules to prohibit leaving the court and jumping forward to contact the serve. Come on, can you imagine someone with Blake Griffin's mobility and a 6'10" frame. That's Karlovic's reach, but with Safin's mobility. Long live the serve and volley!

don

Please see an end of post #92

[uspta146749877]

Final Speed at Ground Contact?

Don,
I have one more question ( embarrassing again):
You have a formula:
Final Speed at Ground Contact=Speed at Net plus Increase

Questions:
1.Do you have a numerical value for a variable Increase?
2.Is it positive or negative ?

[tennis_chiro]

7 foot kicker

Please see an end of post #92

Nice goal. That becomes a whole separate question. I think the height of the kick is largely a function of how high the ball drops from. If you hit a slow rainbow serve, you can probably get a higher kick than a lively ball with a tremendous amount of spin. But the ball with the somewhat lower kick but penetrating through the court is much tougher to return.

Then again, if you are hitting from a higher point, the ball is dropping more and it will have more velocity in the vertical plane as it hits the ground.

Certainly, that ball won't have any trouble clearing the net. That's why I think it is a different question.

don

[tennis_chiro]

The speed due to gravity

Don,
I have one more question ( embarrassing again):
You have a formula:
Final Speed at Ground Contact=Speed at Net plus Increase

Questions:
1.Do you have a numerical value for a variable Increase?
2.Is it positive or negative ?

In this instance, I am referring only to the speed attributable to gravity in the downward direction. That is the only speed that is increasing. Gravity. Works on bullets. Works on tennis balls. Works on everything. Except Superman.

don

[gzhpcu]

Found this which is interesting (Rod Cross, page 383)


Uploaded with ImageShack.us

Some typical serve trajectories are shown for a ball served at 110mph from a height of 9 feet 2 inches. A person of height h serves the ball from a height typically about 1.5 h. For example, a person of height 6 feet usually serves the ball from a point about 9 feet above the court, even if he or she tosses it a lot higher...

The trajectories in the figure were calculated for a serve down the center line so that the ball just cleared the net or that it loanded on the serve line. Results are given for a perfectly flat serve with no spin and for a serve with topspin at 40rev/sec. One of the advantages of serving with topspin is that the range of serve angles is increased (from 1.4degrees to 2.5degrees in this case). If the serve speed is reduced to 85mph and the spin increased to say 50revs/sec for a second serve, the range of available angles increases to 3.8degrees).

The forces to consider when calculating trajectories are force of gravity, drag force and magnus force. The drag force (air pressure on the front of the ball is greater than the air pressure on the back of the ball) is proportional to the ball speed squared. The higher the speed, the greater the drag. An additional force is the magnus force, which arises if the ball is spinning. It forces a ball hit with topspin downwards. If there is a component of slice, then it will also partically swerve sideways. It always acts at right angles to the spin axis and to the drag force.

Plenty of equations in the book.

[uspta146749877]

Slope of a serve

Couple of obvious points here about a last picture posted by Phil:

1.Slopes shown above are smaller than 4 degrees,7 degrees and 10 degrees discussed
previously.

2.I assume that pictures are produced from OBSERVED DATA
(as an opposite to calculated ones)

3.A picture above s NOT in scale-it applies to slopes/angles as well
There is a conjecture that we have the same problems with pictures
posted from Plahenhoef

4.One serve presented does NOT "care" about an acceptance window.

5.Slopes for all serves are NEGATIVE- i.e a derivative of a curve is negative

[uspta146749877]

Simplifications for a spreadsheet of Don

I would suggest to simplify a spreadsheet by Don
by using the following formula

Average speed=(Initial Speed+Final Speed)/2

instead of his

Average speed= (Initial Speed -([2/3].....

It shows at the same time limitations of the Don's derivation(assumptions behind his derivation).

It should be noted that the first formula above is NOT a definition.
It is more or less an assumption

[uspta146749877]

I did NOT answer my questions #1 and #2

In this instance, I am referring only to the speed attributable to gravity in the downward direction. That is the only speed that is increasing. Gravity. Works on bullets. Works on tennis balls. Works on everything. Except Superman.

don

I did NOT answer my questions #1 and #2.Please do.

[uspta146749877]

Related links

John and Don exchanged posts on related question:

http://www.tennisplayer.net/bulletin/showthread.php?t=2&page=85

posts #845 and 846

The basic question was whether a speed number 60 miles per hour was OBSERVED
or CALCULATED.I believe an answer is:"OBSERVED"

[gzhpcu]

Here is a quote from Kundson's "Biomechanical Principles of Tennis Technique", 2006:

Early high-speed studies (early to mid-twentieth century) of the tennis serves of advanced male and female players showed that an initial angle of the ball flight usually between 8 degrees below horizontal up to 10 degrees above. This research on the serves of skilled players was hit very near peak of the racket motion, while the racket was moving upward or transitioning to downward. Only very high-speed serves could initially be hit slightly downward and still clear the net and land in the service box. Most beginners and recreational players served the ball small initial upward trajectories....

Very skilled servers that can hit flat serves over 120 mph may be successful with initial trajectories 8 to 10 degrees below the horizontal. So most players should strive to achieve the feeling of hitting up through the ball so the initial ball trajectory is near the horizontal. Only at more advanced levels can the ball be hit initally downward on a flat serve, but only slightly.

In any case, the closer you are to the net when you serve, the steeper an angle for trajectory of the flat serve you can achieve. Window of acceptance is greater, and you can even hit down more...