Can you (accidentally) hit topspin with an open racket face?

[Attila_the_gorilla]

I did think about gravity, but I admit I did not pursue it too much. So you are relying on the ball falling down to create a little bit of top spin. I would say the spin would be negligible and cannot be calculated using toly's formula. The other reason why I abandoned the gravity idea is that it requires you to to hit a falling ball - it doesn't produce any top spin if the ball is rising when you hit it.

But even if gravity is taken into account, there will be so little top spin that I don't think it can be called a top spin lob. Any time you tap the ball with your racket, it will have a tiny amount of back spin or top spin. What is more, as the ball is in flight, tiny imbalances with cause spin, like in a knuckleball. I wouldn't agree that these qualify as spin lobs.

The reason I used a falling ball and gravity is because it's very easy to understand, using two opposing forces. Of course gravity is constant and the higher force you apply with your racket, its effect becomes more negligible. The point is that asymmetrical force will result in a ball spinning, regardless if the ball is falling or not. The bigger the force (ie faster the racket) and the more away from the centre the ball is hit, the faster the spin. And no this is not a "tiny" amount of spin. This is the reason why there is spin at all.

Strings and string arrangement help this effect by increasing dwell time, friction and snap back, (depending on the kind of string you use), which allows you to just brush on the ball, maximising the distance away from the centre of the ball, thus maximising the asymmetrical nature of the force you apply, thus maximising the amount of spin you get. But you don't need to just brush the very perimeter of the ball to create good top spin.

 

[toly]

Is the racket moving forward (into the court) or backward at contact?

A racquet’s velocity is a vector. I’m going to analyze two previous cases of lobs and evaluate velocities as vectors.
1. Figure 1 - The racquet’s face is vertical, angle A=15°, racquet speed V=65mph.
2. Figure 2 - The racquet’s face is extremely open 70°, angle A=15°, racquet speed V=65mph.

Iincoming ball has zero speed in both instances.

If racquet’s face is vertical, the horizontal component of the racquet’s velocity is very high |VracHor|= 63mph and has forward direction. The vertical component is relatively low |VracVer| = 17mph.

If racquet’s face is open by 70°, the horizontal component of the racquet’s velocity is tremendously low |VracHor|=5mph, but also has forward direction. The vertical component is very high |VracVer| = 64.7mph.
Thus in both cases the racquet moves forward and upward! At the start of trajectories the balls have the same speed and topspin, but awfully different arcs.

 

[sureshs]

I am still not convinced. With an open face and hitting the ball low to high, the 15 degrees off-center line of force you show will not be like that due to deformation of dwell area. Maybe a very slight spin. And certainly this is not due to gravity but to off-center hit.

 

[Cheetah]

gravity is not constant. inverse square rule. hehe just saying... :twisted:

 

[Attila_the_gorilla]

I am still not convinced. With an open face and hitting the ball low to high, the 15 degrees off-center line of force you show will not be like that due to deformation of dwell area. Maybe a very slight spin. And certainly this is not due to gravity but to off-center hit.

Well I've now told the whole story, so just try to dwell on it and see how you go. The reason I used gravity in my example was to make it easier to understand asymmetrical force on a falling ball. This is very easy to demonstrate in practice. Of course gravity and a falling ball are not needed for spin to be produced. Glad you're catching onto the "off-center hit" concept. Same thing applies with side spin.

 

[sureshs]

Well I've now told the whole story, so just try to dwell on it and see how you go. The reason I used gravity in my example was to make it easier to understand asymmetrical force on a falling ball. This is very easy to demonstrate in practice. Of course gravity and a falling ball are not needed for spin to be produced. Glad you're catching onto the "off-center hit" concept. Same thing applies with side spin.

The off-center hit would be more palatable to me if it was a billiard ball being struck by a cue along a line which does not pass through the center of the ball. In the case of deformable strings and balls, that precise line that toly shows is not there.

In any case, point taken. Good find.

 

[mntlblok]

Yes, you can.

A top spin lob is not hit with an open face. I'd love for you to explain what swing path using an open face at the point of contact would result in a top spin lob.

http://twu.tennis-warehouse.com/cgi-bin/trajectory_maker.cgi#output

In the right hand column, change the input from "45" in the "Swing angle" box to "70", and change the input in the "Racquet tilt" box from "5" to "-2". Voila. :mrgreen:

Also, I find everything that Attila sez to be right on target. Coincidence that both he and Rod Cross are down under??

This issue also reminds of something related. I started learning topspin over thirty years ago, when I first started playing. The thing that frustrated me the most was trying to feed balls to an opponent at the net in doubles so that he could warm up his volleys. I simply could *not* give him a good feed. I'd constantly either dip them at his feet, feed them into the net, or hit him some kind of ugly little mishit topspin lob.

I'm prone to taking to experimentation (eventually) when I get frustrated enough, and I finally figured out that I could feed on a decent trajectory without a ridiculous amount of topspin (but still some, if I use a low-to-high swing) if I merely switched to a continental grip - yielding contact with the feed with a slightly open racquet face. As time went on, I started noticing that essentially *all* teaching pro's feed with this grip. Whenever I've asked one of them what grip they feed with, they tell me "continental". I've *never* had one offer that advice otherwise. Some kind of trade secret??

 

[mntlblok]

Previous thread

Fed's swing path isn't flattish; it's shallow. There's a slight difference, because flattish implies a racquet face perpendicular to the ground throughout the swing, and very little low to high.

Most of Fed's "low to high" on his swing comes very near contact, where his violent stretch-shortening in the forearm/shoulder adds a significant upward component in addition to the forward that was built up by the shallow swing path.

Also see this thread, very relevant: http://tt.tennis-warehouse.com/showthread.php?t=374137

Just read that thread and agree with GuyClinch's take. He even danced around the edge of the distinction that I like to make about "swing paths". I like to break it down between the "hand path" and the "racquet head path".

The flatter - or more horizontal - the hand path, the greater the racket head speed will be (in the direction you want to hit the ball, assuming a {near} vertical racket face). I think of that as "hit", as opposed to spin.

Spin, according to the guys who wrote "Technical Tennis" (and know what they're talking about) comes primarily from how fast the racquet is moving "in the plane of the string bed". On a swing with a "flat" "hand path" and no movement in the "plane of the string bed", there would be no (top)spin to speak of.

When Fed uses that relatively flat "hand path", he's still found a way for the racquet to move *massively* in the "plane of the string bed" - using that "doorknob" move. He moves it *very* quickly in that plane, with amazing timing, and only "sometimes" frames it with that dinky little racquet head he uses. :mrgreen:

I think there's too much emphasis placed on what the "wiper" thing does "after" contact, rather than before. The racquet (I'm going back to "racket" - easier to type) head comes from way below his hand to just a bit below it at contact on a medium height ball. The wiper move after contact is merely the result of this late acceleration in the plane of the string bed just before contact. It just don't matter what it does once the ball leaves the racket face.

But, when Fed finishes with the racket head to the side rather than over the shoulder, the racket head has still done pretty much what it always does on anybody's topspin forehand (relative to the hand), but the hand path is flatter - and more powerful. Least that's my theory and I'm sticking to it.:mrgreen:

 

[mntlblok]

topspin lobs

http://twu.tennis-warehouse.com/cgi-bin/trajectory_maker.cgi#output

In the right hand column, change the input from "45" in the "Swing angle" box to "70", and change the input in the "Racquet tilt" box from "5" to "-2". Voila. :mrgreen:

Seems to be quite a range of racket face angles that can be used. Played with a few other combinations of racket face angle and upward swing paths for topspin lobs here: https://www.flickr.com/photos/mentalblock/sets/72157644574943293/