Serve toss question....

[uspta146749877]

A slope of a serve

Hi,
my understanding is that a slope of 1 inc per foot is roughly 7.5 degrees.
Is it correct?

[tennis_chiro]

Slope Courtesy Of Excel

Hi,
my understanding is that a slope of 1 inc per foot is roughly 7.5 degrees.
Is it correct?

Slope to the net w/o gravity
1.607/12 = 0.133916667
arcsin(.1139)= 0.134320201 radians
Degrees of .134 radians = 7.695980646 degrees

Required slope from net to contact w/o gravity
1.0046/12 = 0.083716667
arcsin(.0837)= 0.083814764 radians
Degrees of .0837 radians = 4.802232246 degrees

The 1.607 and 1.004 are from my calculations in my spread sheet above.

This means if you can hit that spot 3 inches above the net, it is pretty easy to get it into the box. But I think Brody said the window was 2 or 3 degrees, not 2 or 3 inches. Obviously, you can't go much lower than 7.6 degrees, but how much higher can you go. If 7.5 degrees dropped the ball almost 60 inches, that's about 8 inches per degree. Therefore the 2 degree acceptance window is about 16 inches. (See Phil's post#61 on the top of page 7 of this thread.) That would seem to make sense.

Now the question is, how does that change as you go forward 4 feet in the court.

Another question would be: (I always considered a good second serve to hit in the last 8".) How tough, degree wise, is it to hit that last 8"? I always thought the more you hit up the more the spin brought you down and that was how we get the ball in deep in the service box consistently (and deep in the court with our groundstrokes.

don

[tennis_chiro]

Reinforcing the importance of getting up

This is a bit of a ridiculous exercise, but I am getting a very tangible feel for the importance of meeting the ball at full extension. And I will probably always remember the size of the "window" for a flat serve and that that window is miniscule for anyone who is not nearly 6 feet tall and hits the serve close to 120mph, even just 110mph.

It also brings me back to my preference for the "exact" (not really but pretty close) toss to the same place each time you serve and catching the ball right near the apex of the toss. If you miss that target by just a little bit, you are significantly diminishing the size of your "acceptance window", especially if you are hitting a big serve, much less a flat one. I come back to my Swiss watch analogy for our Swiss friend. Everything has to fit together perfectly for this to work, but if you can get the toss in the same place every time, you have a pretty good chance. That's why I go nuts about trying to teach my students a repeatable rhythm on their service motion. This "rhythm" I'm talking about is much more important for service effectiveness than the couple of miles an hour you might get by some of the contortions kids are going through these days to get a little more leg drive. When the best guys in the world are 6'4" tall and playing in the world championship semifinals and can't get in 50% of their first serves, something is wrong.

don
alias Mr. "Use Gravity to determine the speed of your toss"

[gzhpcu]

Don,
I appreciate all the work you have gone through,as an approximation.






This is better, based on a ball tracker


All the good servers today hit the ball with an inside-out trajectory in varying degrees, so that the amount of spin is pretty appreciable, really forcing the ball down into the court. Some short players, like Rochus, for example, are among the shortest players on the tour, but thanks to optimal usage of spin on their serves, still manage to hit fast serves.

The advantage for a really tall player, is that on a first serve he can reduce the amount of spin on the hit in order to achieve more power.

[gzhpcu]

Another Hawkeye image, showing curve of a fast first serve:

[tennis_chiro]

Great Illustrations

Another Hawkeye image, showing curve of a fast first serve:

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

[gzhpcu]

Maybe it is also a question of balance. Throwing the ball too much forward and propelling yourself in the air makes balance more difficult IMHO.

[tennis_chiro]

Balance is absolutely necessary

Maybe it is also a question of balance. Throwing the ball too much forward and propelling yourself in the air makes balance more difficult IMHO.

There's no question balance is essential. At the highest levels though, the serve is a condition of controlled imbalance. But I insist the player learn to hit with balance with two feet in place, then with one foot leaving the ground as they reach up to the ball, and then finally even the front foot leaving the ground as they drive up to the ball. It is, however, still not a jump. Even when my best students start to leave the ground and throw the toss forward into the court in a state of "controlled imbalance", they are not jumping. But maybe that is the next stage of development to really through themselves into the court. I just don't think it is worth the tradeoff in accuracy and consistency.

To me, the CAP rule is overarching. Consistency, Accuracy and Power necessarily in that order. The more powerful player only wins when he makes the more consistent player play at a speed where he is no longer consistent. If he isn't consistent enough to do that, his occasionally impressive power isn't going to mean more than an occasional game. Likewise with accuracy. Even in today's game.

But imagine Yao Ming leaning into the court, serving from about 11 feet off the ground (he can touch the rim standing on the court). How would those acceptance windows look? How well could you serve from about 8 feet into the court?! Sure he would need a doubles partner to play the low balls, but he's got half the games in the bag...

oh well, but yes, balance is essential.
don

[uspta146749877]

Two different slopes?

Slope to the net w/o gravity
1.607/12 = 0.133916667
arcsin(.1139)= 0.134320201 radians
Degrees of .134 radians = 7.695980646 degrees

Required slope from net to contact w/o gravity
1.0046/12 = 0.083716667
arcsin(.0837)= 0.083814764 radians
Degrees of .0837 radians = 4.802232246 degrees

The 1.607 and 1.004 are from my calculations in my spread sheet above.

This means if you can hit that spot 3 inches above the net, it is pretty easy to get it into the box. But I think Brody said the window was 2 or 3 degrees, not 2 or 3 inches. Obviously, you can't go much lower than 7.6 degrees, but how much higher can you go. If 7.5 degrees dropped the ball almost 60 inches, that's about 8 inches per degree. Therefore the 2 degree acceptance window is about 16 inches. (See Phil's post#61 on the top of page 7 of this thread.) That would seem to make sense.

Now the question is, how does that change as you go forward 4 feet in the court.

Another question would be: (I always considered a good second serve to hit in the last 8".) How tough, degree wise, is it to hit that last 8"? I always thought the more you hit up the more the spin brought you down and that was how we get the ball in deep in the service box consistently (and deep in the court with our groundstrokes.

don

Don,
I do NOT understand a difference between
"Slope to the net w/o gravity"
and
"Required slope from net to contact w/o gravity"

[uspta146749877]

Comparison with Plagenhoef

I am trying to see whether slopes calculated by Don are in a same ball
park as slopes calculated by Plagenhoef
I understand that 4.8 degrees calculated by Don corresponds to 5 degrees
calculated by Plagenhoef.
I understand that an actual curve of Plagenhoef would be the steepest.

Knudson says:
"Very skilled servers that can hit flat serves 120 mph may be successful
with initial trajectories 8 to 10 degrees below horizontal".
How does it compare with 7.6 degrees calculated by Don?

[uspta146749877]

An initial speed of a ball

I would like to point out that a initial speed of a ball used by Plagenhoef is 102 miles.
An initial speed of a ball from Don's calculations is 120 miles per hour.

I do NOT think it matters a lot-however in formulas of Plagenhoef
a speed of a ball ( v indexed b ) shows in a denominator

[tennis_chiro]

required slope to the spot over the net and then from there

Don,
I do NOT understand a difference between
"Slope to the net w/o gravity"
and
"Required slope from net to contact w/o gravity"

In other words, gravity is responsible for dropping the ball a little less than a foot in the time it takes for the ball to get to the net. If we want to clear the net by 3" and we meet the ball at 9' 6", the slope of our propulsion (might as well start to make this sound like rocket science) of the ball must drop the ball 5' 3" and gravity will take care of the rest getting the ball to 3' 3" off the ground as it passes over the net at the center strap. (And even in singles the net is less than 1" higher for every 2.75 feet we get away from the net strap.)

Of course, since we are not considering spin and wind resistance, and we are factoring out gravity, the slope of the serve will be the same beyond the net. But to understand whether we struck the ball low enough to get it into the court, I factored out the drop due to gravity for the now significantly slower ball to arrive at the necessary downward slope of propulsion of the ball to get the ball to land in the service box. While gravity only drops the ball a little under 12 inches on its journey to the net, it does considerably more in the brief time it goes the last 1/3 of it's journey to the service line because gravity is constantly accelerating the ball downward; hence the 17.65" gravity drop the last 21'. So you would only need about a 5 degree down stroke to get in the court and the 7.5 degree downslope I calculated is more than enough. 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. Of course the "past the net" part of the equation would require a greater than a 5 degree downslope. Without considering spin, I think the acceptance window would be less than 2 degrees.

I'm just trying to find a way to digest and understand the path of the ball by breaking it down a little bit so we recognize the ball is going slower and falling faster from gravity later in its trajectory.

If you followed all that, you earned another piece of pie!
don

[tennis_chiro]

My average speed was 105

I would like to point out that a initial speed of a ball used by Plagenhoef is 102 miles.
An initial speed of a ball from Don's calculations is 120 miles per hour.

I do NOT think it matters a lot-however in formulas of Plagenhoef
a speed of a ball ( v indexed b ) shows in a denominator

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

[uspta146749877]

Please elaborate

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. "

[tennis_chiro]

Height of contact is critical

I am trying to see whether slopes calculated by Don are in a same ball
park as slopes calculated by Plagenhoef
I understand that 4.8 degrees calculated by Don corresponds to 5 degrees
calculated by Plagenhoef.
I understand that an actual curve of Plagenhoef would be the steepest.

Knudson says:
"Very skilled servers that can hit flat serves 120 mph may be successful
with initial trajectories 8 to 10 degrees below horizontal".
How does it compare with 7.6 degrees calculated by Don?

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