I think this is very good video about string and ball friction.
http://www.theatlantic.com/magazine/archive/2011/01/the-new-physics-of-tennis/308339/
Last edited:
The Forehand: Busting misconceptions once and for all
- Thread starter 10isfreak
- Start date
I think this is very good video about string and ball friction.
http://www.theatlantic.com/magazine/archive/2011/01/the-new-physics-of-tennis/308339/
3.5-5.5 ms depending on racquet-head speed, ball speed, string type and tension, racquet stiffness, whether the main strings are free to slide or are stuck, etc. Yes, the faster the shot the less dwell time, which is probably why many pros use very flexible sticks, to increase dwell time.
It's not unusual for the strings to slide 1 cm or more.
My pleasure. The same study found that adding weight at the 3 and 9 o'clock positions reduces this effect. In fact, if you were to add 60 grams of lead tape at 3&9 this effect might be eliminated and high, middle and low impacts would produce approximately the same amount of spin. But that's more lead than anyone puts on a racquet, even Sampras. It could be done, however, but you'd need to start with an extremely light racquet with very low swingweight.
The downside to hitting below center (or above center) is that you lose about 8-9 mph on your shot.
Last edited:
Wegner
Rookie
I think this is good good video – about string and ball friction.
http://www.theatlantic.com/magazine/archive/2011/01/the-new-physics-of-tennis/308339/
Toly,
Great video, very explanatory. And great data about strings coming back into place.
Wegner
Rookie
True, but with today's racquet and string technology (plus great strokes) power is not an issue that cannot be overcome.
T
TCF
Guest
==========================
Last edited by a moderator:
TWU Prof reply
Off the top of my head, I've seen sliding from 5 mm to 30-35 mm. It depends on the speed, angle, spin, pattern, COF, and impact location. It also depends on whether the racquet is hand-held or clamped. That is why you see different results from different tests. I do see bigger displacements with stings that slide.
As to time on strings, that too depends. 5 ms is a good average. It can be as long as 7 ms in the throat and as short as 4 ms at the tip. Again, it will depend on effective mass at the hitting point as well as string stiffness at that location (clamped racquets essentially have "infinite" effective mass). But in general, 5 ms is a very good approximation.
---------------------------------------------------------
So, slide can be fifth of an inch to more than an inch.
Off the top of my head, I've seen sliding from 5 mm to 30-35 mm. It depends on the speed, angle, spin, pattern, COF, and impact location. It also depends on whether the racquet is hand-held or clamped. That is why you see different results from different tests. I do see bigger displacements with stings that slide.
As to time on strings, that too depends. 5 ms is a good average. It can be as long as 7 ms in the throat and as short as 4 ms at the tip. Again, it will depend on effective mass at the hitting point as well as string stiffness at that location (clamped racquets essentially have "infinite" effective mass). But in general, 5 ms is a very good approximation.
---------------------------------------------------------
So, slide can be fifth of an inch to more than an inch.
President
Legend
Serve is the stroke of the past, forehand is the stroke of the future!
Wegner
Rookie
Suresh, perhaps you'd like to start a thread on the serve. I'll be happy to participate. I am in the middle of moving, but next week I'll have more time.
TheCheese
Professional
I'd love to see this happen. Suresh, go for it.
OMG, racquet strings and rolling ball with two bounces!!!
http://youtu.be/ltLxlXvGXqw
So, it is possible!!!???
Last edited:
Wegner
Rookie
Toly, this is tricky, but it can be done by not putting any forward pressure, initially, then bringing the racquet forward. The racquet on the right goes backwards further than the one on the left. You can see how the ball drops vertically when it is gently stopped, then hit forward.
If he was doing the analysis to test the hypothesis that pros hit low on the stringbed intentionally, or even that they hit there more often on topspin drives, for whatever reason, then yes, he should have. But I don't think that was his objective. Anybody with a tennisplayer membership could do their own "study" of the video. I would say 30-50 clear topspin shots per player would be large enough samples to give some meaningful data and shed some light on this notion that players purposely hit below center.
Personally, I suspect that all players attempt to hit the vibration node near the center of the strings, where vibration is eliminated. However, most of us miss it more often than we hit it, especially when swinging fast, because tennis is a difficult sport.
Also, the 8-9 miles per hour lost when hitting above and below the center of the strings is highly significant. I'm not sure the spin boost one gets from hitting below center is worth the loss of pace. 8 miles per hour is an awful lot!
10isfreak
Semi-Pro
There's nearly an average 40% spin rate increase from a center hit when you hit it bellow center... It actually means that you're getting more kick, can afford bigger margin, can manage to hit better angles, etc. 40% is a huge difference.
10isfreak
Semi-Pro
Yandell found that they didn't hit there more often than elsewhere... his only real conclusive answer is simple: players do not hit in the center of the racket. As I stated, the contact location makes spin vary and this affects your trajectory. Depending on how flat you want your shot, what target you want to it or the effect you are looking to get on the other side of the net, the ideal location changes.
To really be conclusive, his study has to cover more than the ball's location because intention or even habits can hardly be drawn from proportions... It does tell that contacts tend to be spread, but it doesn't say why and, accordingly, it doesn't discredit, nor support the statements I included above. Some of these contacts might be mishits, others might be made in different spots due to habits or to fit specific purposes.
Besides, we do not have any number he used. What were the exact data he compiled, which player did he film and how did he manage to know what was the contact point... Doing science is like solving crimes: every possible detail, which may look dumb to an uneducated eye, might actually be very important in further researches. Without his paper and having only with the general outline, we can't do a lot.
As I said, contact points are likely to vary a lot for various reasons and we have to account for a physical reality: ceteris paribus, the lower contact loci grants the player with a much higher spin rate.
10isfreak
Semi-Pro
Samples depend on the test which we will be making, which varies accordingly to the type of variable we face and the sort of relationship we are willing to validate. Considering many variables at once and having properly divided our data into categories which might explain the difference in location, we can use a variance test to evaluate the impact of each category on overall variation. For purely mathematical reasons, the test might be very hard to conduct with only 30 to 50 strokes, or it may not. All depends on the test.
Besides, it doesn't take any high speed video. The contact lasts less than 0,005 seconds and to really get anything near to what SpeedMaster found, we need 200fps or more. Furthermore, you're willing to test the intention of the player, so we might need a context... Ideally, we'd film players, court level, during a training session at super high speed at the same time we film this same sequence, but with the whole court to know what happens, what is the context.
I just wanted to bring people's attention to a fundamental difference between what I have brought and what is being discussed currently:
While being interesting academically and scientifically speaking, the intention or tendencies of pro players in term of contact loci doesn't necessarily lead to manageable improvements in terms of how to play.
Yeah, it's a big increase, but unless you hit there consistently it doesn't do you any good. Because, as you point out, with spin and trajectory varying so much at different locations on the stringbed, if you are counting on that extra spin from a low impact but hit the center instead you're going to get a faster ball with less spin and (probably) a higher trajectory.
Also, aiming to strike 2 inches below center is an invitation for mishits, is it not? The ball is going to slide an inch or so on heavy topspin shots, so if you miss that spot and actually strike 3 inches below center the ball is going to clip the frame as it leaves the "spin window" of the racquet. So yes, the extra spin netted by striking below center could afford a player a greater margin for error in terms of net clearance and depth, but at the same time the risk of clipping the frame is greater. I'm not sure that's a good trade. I'm inclined to think it's a bad one, particularly as the available evidence shows that even the best players in the world are not able to make consistent contact with any particular location of the stringbed. The available evidence shows quite the opposite - that the best the top 3 players in the world can manage is a random-looking impact scatter in a 4-inch diameter zone.
He found that players didn't hit the center of the racquet consistently, and he also found that they didn't hit below center any more than they hit anywhere else. In fact, they tended to hit toward the tip more than any other location. That's three things he found, not one.
The ideal location would change, yes, but isn't just that, an ideal? Can players strike the ideal stringbed location for each shot? That seems unlikely. Maybe in mini-tennis, but with 80 mph incoming balls with heavy and variable spin coming one's way, it seems that trying to hit a particular spot on the stringbed depending on the shot you are trying would be a recipe for disaster.
His study wasn't testing your hypothesis that players intentionally aim to hit below center. That's your study to do. And I think it does, to a limited extent, provide evidence that is contrary to your hypothesis. It appears that Djokovic, Nadal and Federer don't hit any location more than any other, which suggests that they are not able to. If they are, in fact, not able to consistently strike the same spot on the racquet face, at will, then aiming for a spot below center would not be a winning strategy.
You can go to his website and take a look if you're interested. It's copyrighted info, so I can't post it here.
OK, so low impacts produce more spin. But I haven't seen any evidence that top players purposely aim to hit there, nor that they do hit there more than anywhere else on topspin shots. All the arguments I've seen here are persuasive arguments apparently based only on observation and conjecture. You are presenting a hypothesis. But to make a scientific claim there has to be evidence. Do you have evidence or data to support your contention? Did I miss it up-thread?
Last edited:
Chas Tennis
G.O.A.T.
On looking at videos of serves I believe that most servers hit in the top half of the racket face. I have not done stats which are often surprising. I would like to have a more scientific basis for a conclusion and there probably are research papers but I don't know about them.
I have looked at fewer forehands and have done no stats again but I believe that most strong forehand ATP pros (I have not looked at as many WTA forehand videos) hit topspin drives in the bottom half of the racket face. Nothing know as to whether they 'deliberately' hit in the bottom half but I believe that that do. They may not know where they hit very accurately unless they use high speed video.
How would you bet on the question? - Do most pros hit forehand drives by contacting the ball in the top half of the racket or in the bottom half? Would you need odds to bet?
Interested parties can find high speed videos of top 20 players that show top spin forehands where the position of the ball contacting the face can be clearly seen. These are hard to find as the shutter speed has to be fast to reduce motion blur and the frame rate had to be high >200 fps to increase the chance of catching the ball in contact with the strings. The ball has to be seen in contact with the strings otherwise it can be deceptive due to the viewing angle. No cherry picking, randomly accept whatever videos clearly show the impact location... You might also note how the racket face turns just after impact. Identify the video and give the seconds shown on the screen. Post results - top half - estimate from center or bottom half estimate from center. How to divide the racket face into fractional areas since inches are more difficult to calibrate........?
Youtube or Vimeo do not have good stop action. If you click the play-pause button with your mouse as fast as possible you often can get ball contact.
CORRECTION: I just used YT on this video and could use the forward and backward arrows to stop action single frame. This is a big improvement.
Tennisplayer.net has stop action as well as some other sites. In Quicktime the forward and backward arrows are used for single frame.
About 50 observations total should show how often the pros are hitting forehand drives in the top or bottom half of their racket faces. If a few good citizens could do 10-15 each we could get a preliminary answer.
I have looked at fewer forehands and have done no stats again but I believe that most strong forehand ATP pros (I have not looked at as many WTA forehand videos) hit topspin drives in the bottom half of the racket face. Nothing know as to whether they 'deliberately' hit in the bottom half but I believe that that do. They may not know where they hit very accurately unless they use high speed video.
How would you bet on the question? - Do most pros hit forehand drives by contacting the ball in the top half of the racket or in the bottom half? Would you need odds to bet?
Interested parties can find high speed videos of top 20 players that show top spin forehands where the position of the ball contacting the face can be clearly seen. These are hard to find as the shutter speed has to be fast to reduce motion blur and the frame rate had to be high >200 fps to increase the chance of catching the ball in contact with the strings. The ball has to be seen in contact with the strings otherwise it can be deceptive due to the viewing angle. No cherry picking, randomly accept whatever videos clearly show the impact location... You might also note how the racket face turns just after impact. Identify the video and give the seconds shown on the screen. Post results - top half - estimate from center or bottom half estimate from center. How to divide the racket face into fractional areas since inches are more difficult to calibrate........?
Youtube or Vimeo do not have good stop action. If you click the play-pause button with your mouse as fast as possible you often can get ball contact.
CORRECTION: I just used YT on this video and could use the forward and backward arrows to stop action single frame. This is a big improvement.
Tennisplayer.net has stop action as well as some other sites. In Quicktime the forward and backward arrows are used for single frame.
About 50 observations total should show how often the pros are hitting forehand drives in the top or bottom half of their racket faces. If a few good citizens could do 10-15 each we could get a preliminary answer.
Last edited:
dominikk1985
Legend
Regarding the sliding on the strings:
yes the contact time is short but the Speed is also high.
a 100+ mph Forehand with a lot of spin has at least 80 mph RHS.
that is 35 m/s. asuming that the contact time is 3/1000 of a second the racket moves 35/1000*3=0.105m or about 4 inches.
of course not all of this is up since the swing is also Forward but it is not unreasonable that about a third of it (33% upswing angle) is upward which would mean that the racket moves about 1.5 inches up during contact time.
yes the contact time is short but the Speed is also high.
a 100+ mph Forehand with a lot of spin has at least 80 mph RHS.
that is 35 m/s. asuming that the contact time is 3/1000 of a second the racket moves 35/1000*3=0.105m or about 4 inches.
of course not all of this is up since the swing is also Forward but it is not unreasonable that about a third of it (33% upswing angle) is upward which would mean that the racket moves about 1.5 inches up during contact time.
From the TW Professor
http://tt.tennis-warehouse.com/showthread.php?t=451309
---->
Off the top of my head, I've seen sliding from 5 mm to 30-35 mm. It depends on the speed, angle, spin, pattern, COF, and impact location. It also depends on whether the racquet is hand-held or clamped. That is why you see different results from different tests. I do see bigger displacements with stings that slide.
As to time on strings, that too depends. 5 ms is a good average. It can be as long as 7 ms in the throat and as short as 4 ms at the tip. Again, it will depend on effective mass at the hitting point as well as string stiffness at that location (clamped racquets essentially have "infinite" effective mass). But in general, 5 ms is a very good approximation.
----->
The end of the quote
PS #1 The post above does NOT explain whether the CLAMPED HAND experiment has any sense
PS #2 The post above does NOT define effective mass
TW Professor wrote:
http://tt.tennis-warehouse.com/showthread.php?t=451309
---->
Off the top of my head, I've seen sliding from 5 mm to 30-35 mm. It depends on the speed, angle, spin, pattern, COF, and impact location. It also depends on whether the racquet is hand-held or clamped. That is why you see different results from different tests. I do see bigger displacements with stings that slide.
As to time on strings, that too depends. 5 ms is a good average. It can be as long as 7 ms in the throat and as short as 4 ms at the tip. Again, it will depend on effective mass at the hitting point as well as string stiffness at that location (clamped racquets essentially have "infinite" effective mass). But in general, 5 ms is a very good approximation.
----->
The end of the quote
PS #1 The post above does NOT explain whether the CLAMPED HAND experiment has any sense
PS #2 The post above does NOT define effective mass
Last edited:
Julian, your above post consists entirely of something that the TW Professor wrote in reply to question posed by another poster, is that correct? If so, you need to attribute it to the Professor, both to credit the person who wrote it and to avoid confusion about who is saying what here. A simple way to do this would be:
Julian writes: According to the TW Professor, in response to a written query by Sureshs,
"Off the top of my head, I've seen sliding.........."
Some people need to be patient
I do NOT have a laptop at a tennis club I work.
I try to post from a cell -it is a pain.
Cut and past is complex.
Incremental savings are necessary and a screen is small
regards,
Julian
Some people have to be patient
I do NOT have a laptop at a tennis club I work.
I try to post from a cell -it is a pain.
Cut and past is complex.
Incremental savings are necessary and a screen is small
regards,
Julian
Last edited:
I copied this fragment http://youtu.be/ltLxlXvGXqw from HEAD Corp. advertising video http://www.youtube.com/watch?v=JMBqPbLrZMA. They maybe compare good racquet with bad one?
What is your statement?
What is your statement?I copied this fragment http://youtu.be/ltLxlXvGXqw from HEAD Corp. advertising video http://www.youtube.com/watch?v=JMBqPbLrZMA. They maybe compare good racquet with bad one?
This is just fancy video and no statement so far, but I will collect some more data and give you particular statement.
Btw, what is effective mass?
Last edited:
No, it is not.
There is citation from Rod Cross article, PHYSICS OF TENNIS http://www.physics.usyd.edu.au/~cross/tennis.html,
“4. The dead spot of a racquet
Clamp the end of the handle on a table, using your hand to press on the handle, so the rest of the racquet hangs over the edge of the table. Then drop a ball onto the strings at various points. The ball will bounce best near the throat. There is a spot near the tip where the ball doesn't bounce at all. That's the dead spot. At the dead spot, all of the energy of the ball is given to the racquet, and the racquet does not give any energy back to the ball.
The reason is that the effective mass of the racquet at that point is equal to the mass of the ball. The effective mass is the ratio of the force at that point to the acceleration at that point (F = ma so m = F/a). If a ball of mass m collides head-on with another ball of mass m at rest, then the incident ball stops dead and gives all its energy to the other ball.“
This racquet’s property is driving me crazy.:evil:
Last edited:
10isfreak
Semi-Pro
In the first place, I never intended to mean that Yandell was addressing this question. I meant that people were using his results improperly.
Secondly, the claim regarding the contact location doesn't rely on a ball's size spot on the string bed. The effect I am looking to get is a fast closure of the racket face upon contact. Any ball struck bellow the geometric center will make it happen to some extent -- that is, you have half a racket string bed to manage getting it right.
The study the SpeedMaster did divided contacts in terms of racket reaction after impact: stable, closed, opened. That is sweet spot, upper half or lower half. You can err a bit toward the tip, the edge or the throat... it still twists the racket. Maybe I worded it poorly by phrasing it the way I did. In my head, it was very clear that relationship wasn't continuous in the sense that each fraction of an inch would give you more spin, but looking at the sentences I wrote, I wasn't accurate enough.
I did provide a chart with three zones, but it's not clear how to use it. To me, you don't use a marginal analysis to make inferences given qualitative data...
T
TCF
Guest
==========================
Last edited by a moderator:
10isfreak
Semi-Pro
dominikk1985 said:
To give credence to your estimation, let's validate the approximation. Most pros hit at an angle less than 20 degrees and usually higher than 10 degrees (in terms of slope). We could deal with this using the tangent and a 100 units long side in a rectangular triangle.
Tan(20) = x/100 which leads us to 100 tan(20) = x = 36,4
Tan(10) = x/100 leads us to x =17,6
So, between 17,6 percent and 36,4 percent of the vector is oriented upward. With 35 m/s, it's 6,17 to 12,74 mm of upward movement.
We may have a good case to think that, indeed, the ball might move... An alternative possibility is that the ball moves along with the racket during this dwell time; yet an other possibility is that of a combination of sliding ball and moving ball. If we believe SpeedMaster's analysis (that much of spin is generated through the racket tilt and a contact bellow center -- and by bellow, I mean closer to the ground, not the throat), only a fraction of this sliding effect would contribute to spin and this fraction should be less 50%, to say the very least.
A good way of finding if someone is educated or not is asking this person if things like this are complicated or not to understand. If he answers the later, he's either a genius who didn't reveal his conclusions or he sees the tip of the iceberg.
So I think what you saying is the ball is carried by the string some distance. In fact along the target arc, it might get carried more than two ball widths, and the upward part of that is probably what you are calculating. Along with that, the ball also slides along the strings a little.
It is called multitasking. The posting time does not come out of tennis time.
dominikk1985
Legend
I have seen that 18 degree number too but I think that is mostly on balls hit on chest Level. on balls below waist the upward swing angle is probably more than 30 degrees.
when fed hits a low ball he will swing up much more. the upward angle is not only to create spin but also trajectory. to hit a ball at the knees with 3 feet net clearance you Need quite a bit of lift.
here is a nadal FH on a low ball with more than 45 degrees upward swing
http://www.youtube.com/watch?v=NSr6dfxhMUw
and here are higher balls with a flatter swing (more like 25 degree I estimate)
http://www.youtube.com/watch?v=NSr6dfxhMUw
and on chest high balls he will swing probably even flatter. swing trajectory has a Lot to do with strike height.
Povl Carstensen
Legend
Subtle difference between the low and high balls...
What is your statement,please?
What is your statement,please?This is just fancy video and no statement so far, but I will collect some more data and give you particular statement.
Btw, what is effective mass?
OK, got it.
No, it is not.
There is citation from Rod Cross article, PHYSICS OF TENNIS http://www.physics.usyd.edu.au/~cross/tennis.html,
“4. The dead spot of a racquet
Clamp the end of the handle on a table, using your hand to press on the handle, so the rest of the racquet hangs over the edge of the table. Then drop a ball onto the strings at various points. The ball will bounce best near the throat. There is a spot near the tip where the ball doesn't bounce at all. That's the dead spot. At the dead spot, all of the energy of the ball is given to the racquet, and the racquet does not give any energy back to the ball.
The reason is that the effective mass of the racquet at that point is equal to the mass of the ball. The effective mass is the ratio of the force at that point to the acceleration at that point (F = ma so m = F/a). If a ball of mass m collides head-on with another ball of mass m at rest, then the incident ball stops dead and gives all its energy to the other ball.“
This racquet’s property is driving me crazy.:evil:
Here is a tool that shows the effective mass (also called "hittingweight") at various impact locations for most racquets produced in the past five years: http://twu.tennis-warehouse.com/cgi-bin/hittingwtrac.cgi You can open up several windows to compare racquets.
Hittingweight is pretty much proportional to swingweight for impacts along the longitudinal axis, with balance point and static mass playing only a small role. Twistweight (or polar moment of inertia) becomes a factor for impacts to either side of the long axis. The hittingweight at the balance point equals the static mass of the racquet and decreases the further away from the balance point you go. So it's tiny at the tip and butt of the racquet.
And here is a tool at USRSA that lets you play with swingweight, balance and static mass and see the effective mass along the longitudinal axis: http://www.racquettech.com/store/learningcenter/lc_effectivemass.html
And this USRSA tool adds twistweight, allowing calculation of impacts at locations not on the longitudinal axis: http://www.racquettech.com/store/learningcenter/lc_effectivemassgeneral.html
Also, if you spend much time reading old articles by Cross, Brody and other physicists studying racquets you'll run into lots of estimations of apparent coefficient of restitution (ACOR). These articles were all written prior to the creation of Tennis Warehouse University, where nearly every racquet produced in the past five years has had its ACOR measured experimentally, rather than estimated mathematically. This is probably the most useful tool to access the ACOR ("Power Potential") database, as it allows a comparison between two racquets with the specs of those racquets clearly listed: http://twu.tennis-warehouse.com/learning_center/contours.php ACOR is pretty much proportional to hitting weight, with some minor role played by twistweight on off-center impacts, stiffness on impacts near the tip of the racquet. String pattern has a general, but small, effect on ACOR.
Last edited:
The thread went a wrong direction
The thread went a wrong direction
The only interesting aspect is a technique to generate a VERTICAL component of forehand AND some progressions related to it
IMHO only three websites provide some info on the subject of the vertical component
1.mention above
2.Heath Waters
3.John Yandell
Positioning of a knuckle and pronation/supination related issues can be discussed.
http://www.youtube.com/watch?v=NSr6dfxhMUw is probably a good starting point
More or less the conversation is related to what John Yandell and Brian Gordon and Macci describe as "flip"
If you want to get in touch with me via E-mail you are welcome to do so
Regards,
Julian Mielniczuk
PS #1
A vertical component of forehand achieves a HALF of the value of a HORIZONTAL component
in 1/20 of time the HORIZONTAL component achieves the max value
It is explains some problems with consistency/shanking/wrist injuries etc
10isfreak,
The thread went a wrong direction
The only interesting aspect is a technique to generate a VERTICAL component of forehand AND some progressions related to it
IMHO only three websites provide some info on the subject of the vertical component
1.mention above
2.Heath Waters
3.John Yandell
Positioning of a knuckle and pronation/supination related issues can be discussed.
http://www.youtube.com/watch?v=NSr6dfxhMUw is probably a good starting point
More or less the conversation is related to what John Yandell and Brian Gordon and Macci describe as "flip"
If you want to get in touch with me via E-mail you are welcome to do so
Regards,
Julian Mielniczuk
PS #1
A vertical component of forehand achieves a HALF of the value of a HORIZONTAL component
in 1/20 of time the HORIZONTAL component achieves the max value
It is explains some problems with consistency/shanking/wrist injuries etc
Last edited:
OK, I see what you're saying. It would make sense that any hit below center would generate more spin, if we assume a gradient from 2" from center, where 30+% more spin is generated, compared to the center. So, possibly, impacts 1" from center might generate 15% more spin then center impacts. There might be a linear spin gradient from the edge toward the center, in other words. But this is assuming a lot, as the stringbed effects responsible for that extra spin are complex and some of them rely on close proximity to the frame edge.
The rotation effect you mention is one of those effects, but given the physics of racquet rotational instability - twisting moments are much greater the further the impact is from center - one would think that the rotation effect would be much less effective at producing extra spin on impacts 1" from the center than it would be at 2" from the center. But I think another experiment would be needed to sort that out.
For those who are wondering what experiments I'm talking about: http://twu.tennis-warehouse.com/learning_center/location.php
The rotation effect can also be applied by the player if he swings so that the top edge of the racquet is accelerating relative to the bottom edge at contact. This will apply a relatively larger force to the top of the ball than the bottom of the ball, producing more spin, even on impacts at locations other than below center and without the racquet spinning in reaction to the ball impact. Rod Cross gives a good explanation of this in a paper on the physics of the kick serve, see Part II, Section 5. Racquet Rotation here: http://twu.tennis-warehouse.com/learning_center/location.php
So there are several racquet rotation events that can generate extra spin:
1. Impacts below the center of the strings produce more spin, all other things equal, due to various stringbed phenomena, one of which is a result of the off-axis impact causing the racquet to "close", which results in greater force being applied to the "top" of the ball.
2. The player can swing in such a way that the racquet-face is closing during impact. In other words, just before impact it is less closed than during and after impact. This will have a similar effect as above, but is not necessarily dependent on impact location. A player could do this by actively pronating the forearm to close the racquet face through impact. I believe coaches sometimes refer to this as "grinding" the ball to produce additional spin at impact. However, there is not enough time during impact for a player to decide, at that point, to do this. The rotation of the racquet would have to be set in motion prior to contact. (Although this could probably be debated by talking about reflex contractions of the forearm muscles, etc., but I'm not sure it would lead anywhere productive.)
3. Racquet tilt should also be considered along with the above. If a racquet is "closed" during the swing, and that angle remains constant so that it is not rotating during contact as in #2 above, it will still produce more spin for the same physical reason as the two rotation events - the closed racquet face will apply greater force to the top of the ball than the bottom of the ball.
I don't know, but I still think it would be better to aim for the center of the strings, or at least along the longitudinal axis. This would seem to give the greatest chance of producing a good shot, although shot speed and spin will vary each time one misses the center, while reducing the chance of clipping the frame and losing the point outright.
Contact Point Videos & Pictures
I think you are right and thank you for post #192.
Below is set of pictures that show point of contact. They copied from random samplings of following high speed videos:
1. Federer Inside Out Forehand tennisplayer.net https://www.youtube.com/watch?v=z6LmJyNoL8U
2. Sharapova Inside Out Forehand1 http://www.youtube.com/watch?v=uC254i1XN9I
3. AO 2012 Sharapova Easy Short Ball Forehand Winner http://www.youtube.com/watch?v=n9egjkaBnYg
4. AO 2012 Kvitova Forehand Return Serve Winner http://www.youtube.com/watch?v=Bnezy_gBxpY
5. AO 2012 Kvitova Second Serve Return Forehand http://www.youtube.com/watch?v=Z8xrhvDIE50
6. AO 2012 Nadal Down the Line Running Forehand http://www.youtube.com/watch?v=594rg_Lrcjw
7. AO 2012 Djokovic Baseline Forehand http://www.youtube.com/watch?v=f5jWEzDsxWg
8. AO 2012 Djokovic Short Ball Forehand http://www.youtube.com/watch?v=VrEwPvhT3lU
9. AO 2012 Djokovic Down the Line Backhand Winner http://www.youtube.com/watch?v=zlDsdMOXnHw
10. AO 2012 Djokovic First Serve Forehand Return Winner http://www.youtube.com/watch?v=eMECK-D9Dqk
11. Lleyton Hewitt Forehand http://www.youtube.com/watch?v=P4jgaPbHcZY
12. Davydenko Forehand http://youtu.be/hF4dlqFH_v8
IMO the best players don’t have tendency to hit ball below of the racquet longitude axis!!!
I think you are right and thank you for post #192.
Below is set of pictures that show point of contact. They copied from random samplings of following high speed videos:
1. Federer Inside Out Forehand tennisplayer.net https://www.youtube.com/watch?v=z6LmJyNoL8U
2. Sharapova Inside Out Forehand1 http://www.youtube.com/watch?v=uC254i1XN9I
3. AO 2012 Sharapova Easy Short Ball Forehand Winner http://www.youtube.com/watch?v=n9egjkaBnYg
4. AO 2012 Kvitova Forehand Return Serve Winner http://www.youtube.com/watch?v=Bnezy_gBxpY
5. AO 2012 Kvitova Second Serve Return Forehand http://www.youtube.com/watch?v=Z8xrhvDIE50
6. AO 2012 Nadal Down the Line Running Forehand http://www.youtube.com/watch?v=594rg_Lrcjw
7. AO 2012 Djokovic Baseline Forehand http://www.youtube.com/watch?v=f5jWEzDsxWg
8. AO 2012 Djokovic Short Ball Forehand http://www.youtube.com/watch?v=VrEwPvhT3lU
9. AO 2012 Djokovic Down the Line Backhand Winner http://www.youtube.com/watch?v=zlDsdMOXnHw
10. AO 2012 Djokovic First Serve Forehand Return Winner http://www.youtube.com/watch?v=eMECK-D9Dqk
11. Lleyton Hewitt Forehand http://www.youtube.com/watch?v=P4jgaPbHcZY
12. Davydenko Forehand http://youtu.be/hF4dlqFH_v8
IMO the best players don’t have tendency to hit ball below of the racquet longitude axis!!!
Last edited:
I wouldn't buy that counter argument. If they are aiming there they will hit there more than they will hit other locations. To think otherwise is preposterous: All these top players, all trying in vain to strike the ball below the center of the stringbed, and failing, continually, year after year....
Just think, if they could only manage to hit below center consistently, how good they would be!
Besides, if we wanted to know if they are aiming there or not we could just ask them.
tommyfr
Rookie
What a sample, 12 pictures and all middle or above middle!
I have seen 100s of videos and pictures, in my estimate about 50 % are below longitude midline. So I think this sample is not at all closely to being random....very selective...Cheating, in short. Argumentation the Ugly way.
I have seen 100s of videos and pictures, in my estimate about 50 % are below longitude midline. So I think this sample is not at all closely to being random....very selective...Cheating, in short. Argumentation the Ugly way.
dominikk1985
Legend
I asked "our" pro filip peliwo about that.
he said he thinks that he usually hits with a slightly closed face (but is not sure because he doesn't have slow mo-we don't know if he is experiencing the closing after contact or actual contact since that happens so fast), but he is pretty sure that he doesn't hit the ball below Center. of course this is just an anecdote because he is not a scientist and many pros actually don't know what they are doing in Detail since that happens so fast and they do it intuitively since their childhood (a lot of MLB Players think they swing down to contact) but I think it's still interesting to read.
he said he thinks that he usually hits with a slightly closed face (but is not sure because he doesn't have slow mo-we don't know if he is experiencing the closing after contact or actual contact since that happens so fast), but he is pretty sure that he doesn't hit the ball below Center. of course this is just an anecdote because he is not a scientist and many pros actually don't know what they are doing in Detail since that happens so fast and they do it intuitively since their childhood (a lot of MLB Players think they swing down to contact) but I think it's still interesting to read.
Last edited:
Since the likelihood that the ball just hits the racquet longitude axis is almost zero, thus according to your data 50% of ball contacts would be above middle line and 50% below. So, your data also demonstrate that players don’t have tendency hitting the ball below middle line.::evil::
Some of my pictures (1, 4, 7, 10) show impact below middle line.:twisted::evil:
Last edited:
Similar threads
