Physicists, come in! I have a quiz.

[kickingbird]

If you hit a fast forehand with an extreme low to high swing and make contact with the ball with a vertical plane, would the ball's trajectory be like a lob? Will it have lots of spin?

If you answered yes to both, doesn't this mean that it's not possible to hit a heavy ball that is 'net skimming'? (assuming a vertical plane on contact).

My thought is that if you want more spin, you must swing faster and more steeply vertically. However, doesn't the same apply if you want to give more height to a ball? So you can't control these 2 elements separately! If you swing fast low to high not only will you get more spin but more height!?

Anyone solve this puzzle???

 

[JackD]

There are two factors at work in you question the first being trajactory. If we could run a series of swings the first being perfectly horizontal with a vertical raq face at contact the final being a vertical swing still with a vertical raq face you should get higher trajectories as the swings go from horizontal to vertical.

The second factor is topspin effeted by the incoming angle of your raq as well as the overall speed of the swing. Remember that topsin makes the ball go down not up. You are going to impart more spin as you increase the raq towrads the vertical plane as well as if the harder you swing will increase spin. The result on the spin is the ball goes down. So the question of will it look like a lob depends on how fast you swing...or to put it another way can you swing the raq fast enough to bring the higher trajectory ball down so it isn't a lob but rather just a very heavy groundstroke.

You'll notice alot of players when trying to hit a passing shot cross court (heavy topspin) follow through on the same side of there body behind the right ear (for a right handed forehand). The follow through is the result of the increased vertical swing but it isn't a lob because they imparted so much spin that the ball will dip just over the net.

 

[kickingbird]

swing the raq fast enough to bring the higher trajectory ball down so it isn't a lob but rather just a very heavy groundstroke.

Thanks JackD! That's very interesting stuff! This is the kind of conversation I'd like to have with my coach but unfortunately he isn't very into physics it seems...

Maybe this explains why sometimes I am swinging low to high quite viciously but produce a shot with a 'flat trajectory'.

So to follow up on your reply that I've highlighted, does that mean it's not possible to hit a lob (I dunno, 8m up in the air?) that is fizzing with topspin? I suppose most lobs are hit with little spin or a slightly open face on contact for the elevation?

Gee, I want to go out and do some experimenting right now!

 

[kickingbird]

Just to make it even more interesting, how would you explain the incredible height and spin Nadal gets on his forehands? The thought only just crossed my mind.

 

[kevhen]

Closed racquet face will get you more topspin allowing you to have a more upward swing for more height and depth.

 

[papa]

There are many factors that effect the flight path of a ball off your racquet. These would include spin, where on the bounce curve the ball is struck, position of the racquet face, age of the ball, etc.

However, the face of the racquet should be vertical or almost vertical at the contact point. The ball is only on the racquet strings for a fraction of a second - something like 4/100 of a second -- some think less. If the racquet is not vertical/almost vertical at contact, its basically impossible to swing the racquet fast enough to compensate for the difference. You might think you can but the reality is that your either catching the ball early/on its upward bounce, or other factors are kicking in.

High looping forehands generally have a ton of topspin so they can clear the net by several feet of more and still bounce in.

 

[mucat]

Just to make it even more interesting, how would you explain the incredible height and spin Nadal gets on his forehands? The thought only just crossed my mind.

Like JackD said, two things. The topspin will make the ball curve downward, the more topspin, the sooner and faster it dips. The angle of the racket face affect the direction (vertical and horizontal). In your question, it is related to the vertical angle of the racket face. To have higher shot, angle the racket up during contact. To have high pace shot, faster forward racket speed. To bring the ball down faster, more topspin. However, spin and pace is a tradeoff, everyone has a maximum swing speed limit, part of the speed translate to spin, the remaining of the speed moving the ball forward.

 

[Pomeranian]

In response to your question, you have to consider that strings for miliseconds, are not a verticle plane on impact. That's why it's possible to hit with a slightly closed face and make it over. I'm sure that's also a reason why you can hit a heavy ball and low over the net. You have to consider the height of the ball being recieved too, that affects the trajectory of your shot. Most people wouldn't hit a high ball back high over the net, they would hit down on it for a winner.

Also define heavy. Lots of spin or pace? A combination of both? A serve can be really heavy and not clear the net by very much.

Another thing to consider, it's pretty easy to hit low over the net and hit a heavy shot. But a shot's peak height is rarely over net if you hit deep. The peak height is almost always on the other side of the net. So maybe you should ask is it possible to hit a heavy shot with a low peak height.

 

[kevhen]

Papa,

So if you hit a ping pong ball with a closed face, is there enough grip from the paddle and ball to have it move upward with lots of topspin as your swing up on the ball or will the closed face cause the ball to move away from the paddle at the angle of the closed face?

I don't hit tennis balls with a closed face myself but it appears that pros with western grips can hit with a closed face and the ball comes off at a different angle than the face of the racquet which is due to the swing path of the racquet as the ball grips the strings for those 3 milliseconds.

 

[Andres]

(...) as the ball grips the strings for those 3 milliseconds.

30 miliseconds, actually

 

[Saito]

My head started hurting after the second post...

 

[mucat]

Papa,

So if you hit a ping pong ball with a closed face, is there enough grip from the paddle and ball to have it move upward with lots of topspin as your swing up on the ball or will the closed face cause the ball to move away from the paddle at the angle of the closed face?

I don't hit tennis balls with a closed face myself but it appears that pros with western grips can hit with a closed face and the ball comes off at a different angle than the face of the racquet which is due to the swing path of the racquet as the ball grips the strings for those 3 milliseconds.

Interesting, reminded me of playing ping pong with a good sticky paddle and a bad slippery paddle. I remember sticky paddle surface DID grip the ball upward more as I apply topspin, as I remember playing with a old bad paddle, I netted the ball more, it felt like the ball was slipping down. But that was long time ago.

 

[kevhen]

Exactly. Sticky paddle will grip and let you rip topspin while slick doesn't grip to the ball so it comes off low and weak. Tennis ball has more grip than ping pong ball but tennis strings don't have the grip of a good paddle, but the tennis ball does compress to the strings for a longer period if you swing through the ball and we all know that spin gets applied to a tennis ball so it's not slipping on the strings.

 

[papa]

Papa,

So if you hit a ping pong ball with a closed face, is there enough grip from the paddle and ball to have it move upward with lots of topspin as your swing up on the ball or will the closed face cause the ball to move away from the paddle at the angle of the closed face?

I don't hit tennis balls with a closed face myself but it appears that pros with western grips can hit with a closed face and the ball comes off at a different angle than the face of the racquet which is due to the swing path of the racquet as the ball grips the strings for those 3 milliseconds.

Well, as you know we're not talking about ping pong. I must tell you, I don't know a heck of a lot about that game although like everyone else, I've enjoyed it. My thinking is that the dynamics of tennis differ quite a bit from tennis although certain basic principals would apply to both games, I'm sure.

Sometimes, what "appears" the pros are doing is actually quite different from what "actually" is going on because of the tremendous speed involved. I would agree that many times it looks like they hit with a closed face untill you really examine the entire stroke.

 

[Prod]

If you're making contact with the vertical plane and that plane is moving straight up vertically with no horizontal movement, there would be no horizontal force, just vertical force. With no horizontal force imparted on the ball, it would not move horizontally (translational). With just a vertical force, which is perpendicular to the radius of the ball at the point of impact, tremendous torque is applied causing rotational movement. The ball would just spin about its center of mass. Would the ball move up vertically in a translational manner? I'm not sure, but I think slightly due to friction or something. But it's rather pointless to just make contact with the ball with a vertical plane with just a vertical force, you would want some horizontal translational movement to get the ball over the net. Generally, the more vertical force you apply perpendicularly to the ball, the more torque = more spin. But, wouldn't just want spinning ball going upward.

If you want to get technical...
Energy = 1/2mv^2 + 1/2Iw^2 (where m = mass, v = velocity, I = moment of inertia, w = angular velocity)

Torque = Ia = r x F (cross product, depends on sine...a = angular acceleration, r = radius, F = force)

If you're making contact with the ball vertically and the line of force is perpendicular to the radius of the ball, you would get an angular acceleration which means you would get an increase in angular velocity. So the more force you apply in such a manner, the more rotational energy it has, which means more spind. But due to the conservation of energy, the energy you put into the shot must be transfer to the ball (in an ideal environment with no wind resistance, etc). Thus, you would get a decrease in translational energy. So the ball doesn't move faster or higher horizontally or vertically.

 

[papa]

Well, I think all this torque, angular velocity, moment of inertia, etc. is probably correct but lets face it, one doesn't have to be a "whiz kid" to play tennis - didn't someone figure that to play top-flight tennis you only needed an IQ of 88 -- not making this up either.

When I was an undergraduate we had a course in "vectors" which in retrospect probably explains this whole process.

But back to the table tennis for a moment. If I'm not mistaken that "sticky" stuff Kevhen speaks about, wasn't that baned from competition years ago - like in the 80's??

Again, knowing little about the technical aspects table tennis, I would think the comparisons between the two sports have to be carefully examined "before" anyone leaps to conclusions.

For example, the relative hights and distances between the two are tremendous along with the size/weight of the ball, racquet/paddle/ net, etc. It just might be that in table tennis one has to have the paddle at a considerable angle to the table to compensate for some of these factors - I would not argue that. And as Kevhen mentioned, the surface of the paddle are greater factors than they are in tennis because the ball skids somewhat as the ball is struck - I would imagine that the angle of the paddle (used to hit a ball) depends on the material stuck to the paddle. Off the top of my head I would think the smoother/harder the surface the less the angle off perpendicular.

I would also think that "many", if not most shots (table tennis), are made where the ball is two, three, or more times the height of the net (prehaps above and below) - in other words, most shots are either hit down or up. I would also believe that although a table tennis ball travels at good speed (maybe as fast as a tennis ball, don't know) it traverses the table in less time than in tennis which becomes another factor.

It just seems to me that the anology between the two sports is probably slight.

 

[Prod]

true, you don't have to be a "whiz kid"...seriously, if you are to calculate and figure out all of this physics stuff while playing, you won't get anywhere. Since the OP asked for a physics related answer, I gave it to him/her. It's fascinating to think about the physics behind tennis, but do you really need an indepth scientific explanation of how to hit with topspin or would you rather go out and experiment and try it for yourself? What matters is that you can get the ball over the net and beat your opponent, physics doesn't matter much when you're playing.

 

[mucat]

<snip>
But back to the table tennis for a moment. If I'm not mistaken that "sticky" stuff Kevhen speaks about, wasn't that baned from competition years ago - like in the 80's??

Again, knowing little about the technical aspects table tennis, I would think the comparisons between the two sports have to be carefully examined "before" anyone leaps to conclusions.

For example, the relative hights and distances between the two are tremendous along with the size/weight of the ball, racquet/paddle/ net, etc. It just might be that in table tennis one has to have the paddle at a considerable angle to the table to compensate for some of these factors - I would not argue that. And as Kevhen mentioned, the surface of the paddle are greater factors than they are in tennis because the ball skids somewhat as the ball is struck - I would imagine that the angle of the paddle (used to hit a ball) depends on the material stuck to the paddle. Off the top of my head I would think the smoother/harder the surface the less the angle off perpendicular.

I would also think that "many", if not most shots (table tennis), are made where the ball is two, three, or more times the height of the net (prehaps above and below) - in other words, most shots are either hit down or up. I would also believe that although a table tennis ball travels at good speed (maybe as fast as a tennis ball, don't know) it traverses the table in less time than in tennis which becomes another factor.

It just seems to me that the anology between the two sports is probably slight.

The more sticky paddle I was talking about was just a newer and better paddle, it was a legal paddle. As the paddle surface get old, they usually lose the grip.

The relation between contact angle (both horizontal and vertical), ball travel direction and spins still apply to both sport. I found beginners in tennis have difficulty understanding spins and how to apply them. But for those beginner with table tennis knownlege, they will understand spins and can use them right away.

 

[papa]

The more sticky paddle I was talking about was just a newer and better paddle, it was a legal paddle. As the paddle surface get old, they usually lose the grip.

The relation between contact angle (both horizontal and vertical), ball travel direction and spins still apply to both sport. I found beginners in tennis have difficulty understanding spins and how to apply them. But for those beginner with table tennis knownlege, they will understand spins and can use them right away.

Well, as I've stated, I don't know much about the technical aspects of table tennis. The "sticky paddle" I was referring to was quite some time ago in some international meet - seems to me it was fifteen or twenty years ago but I might be wrong. Quite frankly, I don't know whats legal in the way of the rubber facing for paddles - I've just kinda picked up whats available and played. Not trying to put the sport down in any way, just trying to show that I don't know very much about it other than the obivious.

My comments where intended to be directed at the angle of the paddle when one strikes the ball compared to what they are in tennis. In tennis, as you probably know the racquet head should, for all practical reasons, be vertical or close to it. In table tennis it seems that this angle (because of previous comments people have had) might be more off the vertical - I was simply trying to offer an explanation of why this might be so.

 

[paulfreda]

Hawaiian FH Grip

If you hit a fast forehand with an extreme low to high swing and make contact with the ball with a vertical plane, would the ball's trajectory be like a lob? Will it have lots of spin?

If you answered yes to both, doesn't this mean that it's not possible to hit a heavy ball that is 'net skimming'? (assuming a vertical plane on contact).

My thought is that if you want more spin, you must swing faster and more steeply vertically. However, doesn't the same apply if you want to give more height to a ball? So you can't control these 2 elements separately! If you swing fast low to high not only will you get more spin but more height!?

Anyone solve this puzzle???

I think you are committing a logical fallacy here assuming the 2 elements are inseparable. Nevermind the physics, I can tell you that with my Hawaiian FH grip I can hit a low screamer with tremendous topspin over the net with this grip. That is why I love it.

How do I do it ? That would take a while to explain.

Why does it work ? I am too tired and busy to come up with the physics, but I can tell you it is not as simple as some would think.

 

[mucat]

My comments where intended to be directed at the angle of the paddle when one strikes the ball compared to what they are in tennis. In tennis, as you probably know the racquet head should, for all practical reasons, be vertical or close to it. In table tennis it seems that this angle (because of previous comments people have had) might be more off the vertical - I was simply trying to offer an explanation of why this might be so.

I think in both sport, for topspin, can be hit with both vertical or close. That why I think in this aspect, it is very similiar. The ball slipping and sliding downward at contact only happen with really old and/or really bad paddle. But the technique and muscle use to play tennis and table tennis are very different though.