Serve toss question....

[uspta146749877]

Units missing in a Don's spreadsheet

Some variables are missing units in a Don's spreadsheet
TNetToCrt should be in secs
Increase in Speed of Gravity Ball Drop should be in feet per second
Speed of Gravity Drop at Net should be in feet per ssecond
Avg... should be in feet per second
Gravity dropped the ball 11.5 ... ( should be replaced by 11.5 inches)

[uspta146749877]

Your conclusion

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



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...

1.Your quote: "in any case ..."
It is what Don is trying to prove.Let us try to keep a question open.

2.Interestingly enough I quoted Knudson in this thread like a week ago-
please see

http://www.tennisplayer.net/bulletin/showthread.php?t=1702&page=6

post #57

julian mielniczuk Ph.D. uspta certified pro juliantennis@comcast.net
www.julianmielniczuk.usptapro.com Courtside Tennis Club,Bedford,MA

[gzhpcu]

1.Your quote: "in any case ..."
It is what Don is trying to prove.Let us try to keep a question open.

Am confused here. It is pure and simple geometry. The trajectory from the racket to the serve box steepens the closer you get to the net, doesn't it?

[uspta146749877]

I completely disagree

Am confused here. It is pure and simple geometry. The trajectory from the racket to the serve box steepens the closer you get to the net, doesn't it?

I completely disagree.
I will respond at the end of a day today.

Even if you would change the word "serve" to "flat serve" in your sentence above it does NOT have
to be true.
Additionally some quantitative statements could be useful-for example
what would be a slope for a contact of 4 feet inside.

julian mielniczuk Ph.D. uspta certified pro juliantennis@comcast.net
www.julianmielniczuk.usptapro.com Courtside Tennis Club,Bedford,MA

[gzhpcu]

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Two impact points: the red for on the baseline, the green for closer in. What do you disagree with?

[tennis_chiro]

Not necessarily

Am confused here. It is pure and simple geometry. The trajectory from the racket to the serve box steepens the closer you get to the net, doesn't it?

The question is complicated by the fact that reaching into the court lowers teh contact point. It also reduces the time the ball has to drop to the level of the court due to gravity.

There are two obstacles or goals. First, get over the net. Second, get down to the surface before the service line.

It may be as simple as fundamental geometry, but gravity complicates things a little bit.

don

[uspta146749877]

Mechanics

The question is complicated by the fact that reaching into the court lowers teh contact point. It also reduces the time the ball has to drop to the level of the court due to gravity.

There are two obstacles or goals. First, get over the net. Second, get down to the surface before the service line.

It may be as simple as fundamental geometry, but gravity complicates things a little bit.

don

It is NOT obvious that biomechanics will be the same for two cases:
one foot forward toss
vs
four feet forward toss
By the way: all this discussion about "an acceptance window" complicates
all analysis here.Can be drop "an acceptance window" dead for couple hours/days?
julian mielniczuk Ph.D. uspta certified pro juliantennis@comcast.net
www.julianmielniczuk.usptapro.com Courtside Tennis Club,Bedford,MA

[gzhpcu]

The question is complicated by the fact that reaching into the court lowers teh contact point. It also reduces the time the ball has to drop to the level of the court due to gravity.

There are two obstacles or goals. First, get over the net. Second, get down to the surface before the service line.

It may be as simple as fundamental geometry, but gravity complicates things a little bit.

don

On a high speed serve, the effect of gravity is very small. The big effect is on a slow serve. When a fast serve dips, that is mostly due to the magnus effect. The lowering of the contact point when the ball is thrown ahead has less effect than the shorter distance.

[uspta146749877]

Is it OK for a ball to go up first BEFORE it goes down?

Am confused here. It is pure and simple geometry. The trajectory from the racket to the serve box steepens the closer you get to the net, doesn't it?

Is it OK for a ball to go up first BEFORE it goes down?

[gzhpcu]

Is it OK for a ball to go up first BEFORE it goes down?

Only for a heavy topspin serve or my grandmother's serve...

[uspta146749877]

All those sentences are conjectures

On a high speed serve, the effect of gravity is very small. The big effect is on a slow serve. When a fast serve dips, that is mostly due to the magnus effect. The lowering of the contact point when the ball is thrown ahead has less effect than the shorter distance.

All those sentences are conjectures-you should really produce some numerical results.
There are some constants in

http://www.fuzzyyellowballs.com/articles/tennis-physics/the-magnus-effect-equation/

which can be discussed.
If required I can try to find a better source of a reference
An equation quoted overthere is
F=1/2 *rou*V*V*A*Cl

Don will have all the books in couple of days and he will have a more fair chance
to discuss an issue mentioned above.I will be probably out of picture
to make eveybody happy.
It remains an open question : how large is an Magnus force/Magnus effect when
a serve is flat or ALMOST flat

julian mielniczuk Ph.D. uspta certified pro juliantennis@comcast.net
www.julianmielniczuk.usptapro.com Courtside Tennis Club,Bedford,MA

[uspta146749877]

For Don

I am quitting.It gets to difficult.It is down to 2.
Please read my E-mail.

julian mielniczuk Ph.D. uspta certified pro juliantennis@comcast.net
www.julianmielniczuk.usptapro.com Courtside Tennis Club,Bedford,MA

[uspta146749877]

One green serve is ALMOST long

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Two impact points: the red for on the baseline, the green for closer in. What do you disagree with?

Let us start from something simple
One green serve is ALMOST long.Tennis is a percentage game.
Would every pro take very high risks?

[gzhpcu]

All those sentences are conjectures-you should really produce some numerical results.
There are some constants in

http://www.fuzzyyellowballs.com/articles/tennis-physics/the-magnus-effect-equation/

which can be discussed.
If required I can try to find a better source of a reference
An equation quoted overthere is
F=1/2 *rou*V*V*A*Cl

Don will have all the books in couple of days and he will have a more fair chance
to discuss an issue mentioned above.I will be probably out of picture
to make eveybody happy.
It remains an open question : how large is an Magnus force/Magnus effect when
a serve is flat or ALMOST flat

julian mielniczuk Ph.D. uspta certified pro juliantennis@comcast.net
www.julianmielniczuk.usptapro.com Courtside Tennis Club,Bedford,MA

The distance a ball drops due to gravity is y=gt^^2/2, where g=9.8m/s^^2 is the acceleration due to gravity. After 0.1 seconds, y=0.049m and after 0.2s, y=0.196m.

Formula for drag force F=C A d v^^2/2, C= drag coefficient, = 0.55. A is the cross-section of the ball =pi x R^^2, R=radius of the ball. .d=density of air = 1.21 kg/m^^2. A ball experiences a back force F = 0.55 x 0.00342 x 1.21 x v^^2/2 = 0.00114 x v^^2 Newton. If v=30m/sec (180 km/hour), then F=1.026 Newton.

Force of gravity on the ball is =mg. m=0.057 kg for an average tennis ball. So 9.8 x 0.057= 0.559 Newton. Comparing this to the force of gravity on the ball: drag is twice as much as gravity.

The magnitude of the Magnus force on a tennis ball is similar to the drag force equation.
F=( 1/(2 + (v/vspin)) A d v^^2)/2 , where vspin = R x (angular speed about a horizontal axis perpendicular to the flight of the ball). Angular speed is about 16 to 80 revs per second. If v=30m/s, w about 60 revs per second, with R=0.033m, then vspin = 9.9m/s, v/vspin= 3.03. Equation shows that the Magnus force is smaller than the drag force, but can approach it the bigger the spin.

[gzhpcu]

Let us start from something simple
One green serve is ALMOST long.Tennis is a percentage game.
Would every pro take very high risks?

Don't think you understand the diagram: the green shows the two extremes, just over the net and still in the court - over the net and still in the serve box. The angle between the two extremes is larger than in the red case, ergo, higher percentage in.