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tennis_pr0
11-08-2009, 02:52 PM
Just wondering, but if a hand held radar gun is placed directly behind the net, (which means the gun is about 40 feet from the server), how much, or what percentage of velocity is lost from the time it takes to go from the racquet to the net. The head pro at the club I teach as said around 20-30%, but I just wanted to know if this was correct or if anyone knows the calculation for this. Thanks.

5263
11-08-2009, 04:19 PM
Just wondering, but if a hand held radar gun is placed directly behind the net, (which means the gun is about 40 feet from the server), how much, or what percentage of velocity is lost from the time it takes to go from the racquet to the net. The head pro at the club I teach as said around 20-30%, but I just wanted to know if this was correct or if anyone knows the calculation for this. Thanks.

That would be in the ball park for sure. It does depend to some extent on the radar gun, as they have different pickup ranges.
There is also the aspect of how much off angle the pick up is too , as the radar is more accurate the more it is inline with the shot. On the ground near the net is not only far from best pick up, but also is well offline of any serve that would be good.

drakulie
11-08-2009, 04:39 PM
the bushnell (speling) is a "hand-held" radar device, and it is supposed to pick up the speed of the ball as soon as contact is made. The speedtrac is not hand-held, and needs to be placed near the net. This device picks up the speed as it approaches the device, so the reading is a bit lower than the actual speed at contact. However, 20-30% even for this device is way too much. more like 5-10% depending on how far the device is from the server.

tennis_pr0
11-08-2009, 04:43 PM
Right, well they say that a serve loses 50% of its velocity when it reaches the opponent, so a 130 mph serve is actually only about 70 or so when it reaches the other player.

Fedace
11-08-2009, 04:49 PM
Just add 5-8 mph to the reading and you will be accurate.. i am talking about speedtrack, of course. Bushnell is the most accurate means of testing serve speed. That is why it is used for the Fast serve competition that is held Nationally each year...

5263
11-08-2009, 04:50 PM
I guess you can choose who to believe. I don't know how a bushnell is supposed to pick up a serve at contact from just anywhere, not to mention; which bushnell. I own a busnell and it sure is not capable of that. Anyone with radar experience can explain that to you and 5% is not even close for a speed check on the other side of the net. The past radars even used in the pros were off almost that much just for out wide serves due to alignment.

tennis_pr0
11-08-2009, 04:56 PM
well we know the serve loses a considerable amount of velocity, I think adding 25% to a radar gun at the net is the most accurate.

drakulie
11-08-2009, 04:57 PM
Right, well they say that a serve loses 50% of its velocity when it reaches the opponent, so a 130 mph serve is actually only about 70 or so when it reaches the other player.


yes, but the speedtrac does not pick up the speed right at the net. It picks it before it reaches the net.

I have one, have taken several serve speeds and compared it to a forumula which provides accurate serve speed calculations. Like I said, it is between 5-10%.

chess9
11-09-2009, 04:55 AM
the bushnell (speling) is a "hand-held" radar device, and it is supposed to pick up the speed of the ball as soon as contact is made. The speedtrac is not hand-held, and needs to be placed near the net. This device picks up the speed as it approaches the device, so the reading is a bit lower than the actual speed at contact. However, 20-30% even for this device is way too much. more like 5-10% depending on how far the device is from the server.

Yes, I'd agree for most serves. 20% might be a bit too high, depending on the quality of the calibration of the two instruments, and some ambient factors (humidity and wind speed will have more effect on a faster serve).

Neither 'radar' is instrument grade, so, take any of their readings cum granulo salis.

-Robert

Fedace
11-09-2009, 06:29 AM
yes, but the speedtrac does not pick up the speed right at the net. It picks it before it reaches the net.

I have one, have taken several serve speeds and compared it to a forumula which provides accurate serve speed calculations. Like I said, it is between 5-10%.

which translates to if you add 5-8 mph, you are in the ballpark, right ? so if it registers 93 mph on the serve then i am really serving 98-100 mph, am i right ?

drakulie
11-09-2009, 07:35 AM
^^^correct. This is if you have the radar near the net facing you.

However, if you placed the radar on the opposite side of the net (a few feet away from the net), it would register a slower speed. The further the radar is from the server, the slower the speed registered.

5263
11-09-2009, 10:30 AM
Just wondering, but if a hand held radar gun is placed directly behind the net,

plus the alignment issue for at least 5%.
which is also an error often for vid technique,
and is mentioned by Mike.
so in this case you have one error, masked by
the same error in the backup technique.

Ripper014
11-09-2009, 10:44 AM
Right, well they say that a serve loses 50% of its velocity when it reaches the opponent, so a 130 mph serve is actually only about 70 or so when it reaches the other player.

Most of the speed is lost when the ball is coming off the court. And I agree that you want to be measuring the speed of the ball leaving the racket face.

5263
11-09-2009, 10:49 AM
Most of the speed is lost when the ball is coming off the court. And I agree that you want to be measuring the speed of the ball leaving the racket face.

Not exactly true. Yes, much speed is lost on the bounce, but not most of the loss. Most is drag from air over the distance.

Ripper014
11-09-2009, 12:51 PM
Not exactly true. Yes, much speed is lost on the bounce, but not most of the loss. Most is drag from air over the distance.

I will accept your word for it... but intuitively I would think that more energy would be displaced when hitting a fixed object than what might be lost due to friction over 70 or so feet.

5263
11-09-2009, 12:59 PM
I will accept your word for it... but intuitively I would think that more energy would be displaced when hitting a fixed object than what might be lost due to friction over 70 or so feet.

What you say makes sense, but I guess it is due to the deflection angle allowing it to hold some good speed. A light fuzzy ball really has lots of drag effect. It is really quite amazing.

TenniseaWilliams
11-09-2009, 01:33 PM
What you say makes sense, but I guess it is due to the deflection angle allowing it to hold some good speed. A light fuzzy ball really has lots of drag effect. It is really quite amazing.

It would be amazing if it were true.

The bounce slows the ball more than air drag in most situations.

5263
11-09-2009, 01:49 PM
It would be amazing if it were true.

The bounce slows the ball more than air drag.

care to explain what you say?

I based my comment on the study below and what I've seen on hawk-eye data. Look like the bounce is responsible for less than half of the speed loss to here and other things I've seen on this.

Ball Speed in Pro Tennis

The team found that the maximum speed recorded by the radar guns on the serve corresponded very closely with the computer program analysis. For the 23 first serves for which the team had radar gun readings, the average speed was 117mph. For the same 23 serves, the average maximum speed calculated by our software program was 121mph, a difference of about 3.5%.

What the spectators saw on the radar guns was probably extremely accurate, but what about what they couldn't see? The results of the analysis were clear--the ball slows down dramatically after the hit in pro tennis, both on the serve, and on all the other shots. By the time the ball had bounced on the court, every Sampras shot had lost roughly 50% of its initial speed. By the time the opponent returned the ball, or it crossed the baseline out of play for a winner, this number could reach as high as 60%.

What did that mean in terms of the individual shots, starting with Sampras's most famous shot--his first serve? In total 29 first serves (including the 23 with matching radar gun numbers) were analyzed. The program showed that the average maximum speed of these serves was 120mph.

Before the serves bounced in the service box, this average speed was down to 87mph. The air resistance, i.e., the drag as the ball traveled through the air, had already reduced the ball speed by over 30mph.

But the bounce of the ball on the court--an event that lasts only around .004 of a second--reduced the speed even more. Sampras's first serves went from an average of 87mph just before the bounce to an average of 62mph after the bounce. This was a loss of another 25mph in a tiny fraction of a second.

Taken together then the air resistance during the flight of the ball and friction of the bounce on the court reduced the average speed from 120mph to just over 60mph -- about half the initial velocity.

TenniseaWilliams
11-09-2009, 02:05 PM
care to explain what you say?

I based my comment on the study below and what I've seen on hawk-eye data. Look like the bounce is responsible for less than half of the speed loss to here and other things I've seen on this.

Ball Speed in Pro Tennis

The team found that the maximum speed recorded by the radar guns on the serve corresponded very closely with the computer program analysis. For the 23 first serves for which the team had radar gun readings, the average speed was 117mph. For the same 23 serves, the average maximum speed calculated by our software program was 121mph, a difference of about 3.5%.

What the spectators saw on the radar guns was probably extremely accurate, but what about what they couldn't see? The results of the analysis were clear--the ball slows down dramatically after the hit in pro tennis, both on the serve, and on all the other shots. By the time the ball had bounced on the court, every Sampras shot had lost roughly 50% of its initial speed. By the time the opponent returned the ball, or it crossed the baseline out of play for a winner, this number could reach as high as 60%.

What did that mean in terms of the individual shots, starting with Sampras's most famous shot--his first serve? In total 29 first serves (including the 23 with matching radar gun numbers) were analyzed. The program showed that the average maximum speed of these serves was 120mph.

Before the serves bounced in the service box, this average speed was down to 87mph. The air resistance, i.e., the drag as the ball traveled through the air, had already reduced the ball speed by over 30mph.

But the bounce of the ball on the court--an event that lasts only around .004 of a second--reduced the speed even more. Sampras's first serves went from an average of 87mph just before the bounce to an average of 62mph after the bounce. This was a loss of another 25mph in a tiny fraction of a second.

Taken together then the air resistance during the flight of the ball and friction of the bounce on the court reduced the average speed from 120mph to just over 60mph -- about half the initial velocity.

Sure! If you read your example carefully, you will see that the ball lost about 33mph in the air, and about 25mph in the bounce.


So the ball lost 27.5% speed in the air, but was slowed 28.7% from the bounce.

This example I found comes with a lot of math explaining how things like angle of incidence and court speed usually result in 30%-60% loss in bounce, with air resistance pretty much fixed at around 25%.

Obviously, this doesn't hold true when the ball path goes extremely vertical.

p345 Physics and Technology of Tennis

For example, a ball served at 100mph will slow down through the air and hit the court at about 75mph. It then bounces off the court at about 50mph.

This example shows a 25% drop in the air, and then a 33% loss on bounce.

5263
11-09-2009, 02:10 PM
Sure! If you read your example carefully, you will see that the ball lost about 33mph in the air, and about 25mph in the bounce.

This example I found comes with a lot of math explaining how things like angle of incidence and court speed usually result in 30%-60% loss in bounce, with air resistance pretty much fixed at around 25%.

Obviously, this doesn't hold true when the ball path goes extremely vertical.

p345 Physics and Technology of Tennis

This example shows a 25% drop in the air, and then a 33% loss on bounce.

You are really reaching. clearly half the initial speed was loss due to air drag and half to the bounce, even in your example.
Is your whole purpose to post just to be a pain?

You can continue to post to me if you like, but I'm done with you under this user name as well as the other one you use.

TenniseaWilliams
11-09-2009, 02:13 PM
You are really reaching. clearly half the initial speed was loss due to air drag and half to the bounce, even in your example.
Is your whole purpose to post just to be a pain?

I can see you're not big on this science and math stuff.

5263
11-09-2009, 02:27 PM
This ignore feature is really nice. I think this forum can be a ton more enjoyable without the mindless spam of those who just want to annoy.

Ripper014
11-09-2009, 02:34 PM
Sure! If you read your example carefully, you will see that the ball lost about 33mph in the air, and about 25mph in the bounce.


So the ball lost 27.5% speed in the air, but was slowed 28.7% from the bounce.

This example I found comes with a lot of math explaining how things like angle of incidence and court speed usually result in 30%-60% loss in bounce, with air resistance pretty much fixed at around 25%.

Obviously, this doesn't hold true when the ball path goes extremely vertical.

p345 Physics and Technology of Tennis

This example shows a 25% drop in the air, and then a 33% loss on bounce.



Actually if you do the math he is right... I don't have a calculator on me... but 120mph to 87mph % difference vs 87mph to 62mph % difference. Like I said earlier, intuitively this makes sense.

TenniseaWilliams
11-09-2009, 02:42 PM
Actually if you do the math he is right... I don't have a calculator on me... but 120mph to 87mph % difference vs 87mph to 62mph % difference. Like I said earlier, intuitively this makes sense.

I am not trolling you, the math and the concepts behind it are quite correct.

Our numeric friend has some issues ...

5263
11-09-2009, 02:45 PM
Actually if you do the math he is right... I don't have a calculator on me... but 120mph to 87mph % difference vs 87mph to 62mph % difference. Like I said earlier, intuitively this makes sense.

Of course, we can play with the numbers and show all kinds of things if you want, but i can't imagine you would look at something other than what % of the initial speed, each part plays. Air drag was about a 30+ mph loss before the bounce and another 5-10 after, which accounts for as much as 42 mph of the total. Quite a bit more than the 25mph loss from the bounce.

But to each his own though and if it makes you feel someone is part right or right, great. Feel the best you can.

5263
11-09-2009, 02:53 PM
Most of the speed is lost when the ball is coming off the court.

If you are interested in those type of word games and twisting, notice you said when the ball is coming off the court. I would expect that the loss has already happened as the ball was coming into the court opposed coming off.

tennis_pr0
11-09-2009, 05:38 PM
These calculations seem to be correct. From what I was told, the ball loses about 25% as it reaches the net, and another 10 or 15% after the box. Your calculations seem to be accurate.