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Post by volleydadtx on Jul 14, 2021 17:56:31 GMT -5
When we were experimenting with the float serve speeds, at least for this particular young athlete, the slower floats were deadly. She passed them but with more difficulty than those coming @ 31-32 mph. They would clear the net and then just drop like a stone.
It reminded me of knuckle ball pitcher R.A. Dickey. His 70 mph floating pitch would make batters look silly.
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Post by mikegarrison on Jul 14, 2021 18:48:17 GMT -5
When we were experimenting with the float serve speeds, at least for this particular young athlete, the slower floats were deadly. She passed them but with more difficulty than those coming @ 31-32 mph. They would clear the net and then just drop like a stone. It reminded me of knuckle ball pitcher R.A. Dickey. His 70 mph floating pitch would make batters look silly. RA Dickey had an unusually fast knuckleball. Typically knuckleball pitches are significantly slower than his was. That's kind of the opposite of what you are saying here about a slow floater being harder to pass. |
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Post by crando on Jul 14, 2021 23:04:57 GMT -5
A couple years back I found this: volleyballmag.com/floatserve/My take is that there's a certain speed at which the volleyball's drag increases significantly -- thus it will drop harder right at the point where air drag slows it down to exactly that speed. What that exact speed is, it's based on the surface of the ball (I believe that a golf ball's dimples help make that speed slower -- so that a golf ball generally never slows down to that exact speed until after it bounces, thus helping it fly longer and straighter), the size-to-weight, the temperature and air pressure, etc. But ideally, you'd want to hit a serve at an initial speed such that air drag slows the ball down to that critical speed at some point after it crosses the net and before it reaches the passers. The ball's flight also becomes its most erratic at a specific speed -- I think the article implies it's the same speed. So around the point at which a serve starts to drop hard, that's when it floats the most. And, intuitively, that makes sense. If a machine serves a ball at 200 mph, it's knifing through the air so fast it won't float. And at low speed, the ball doesn't float much because it's not passing through much air. Similarly, in baseball the knuckleballers don't want to throw too hard, because the ball will track too straight -- there's an exact speed for any given ball on any given day at which it flutters the most. So, I think you multiple by 2.25 (3600 seconds per hour divided by 1600ish meters per mile) from m/s to get mph, and looking at Figure 3 in that article, a conventional ball seems to hit its drag coefficient around 15 m/s, so low 30s in mph. If a ball loses about 1 mph per 7 feet, we want to hit the ball about 5 mph harder than that critical speed -- so the ball starts max-floating and max-dropping somewhere just after crossing the net (maybe 35 feet from the server). A little slower on hot days, or at altitude; a little faster on cold days at sea level. That's the speed for the nastiest serve -- and again, what type of ball changes that exact speed too. Personally, too, I felt like when I took just a little off my max velocity, that's when the ball would float the most (and when the passers would curse at me the most). And I've felt, watching high-level women's/girls, that some kids who just crank their serve don't hit the toughest ones -- in most conditions, it feels like the kids hitting a couple mph less (38 mph off the hand, instead of 40-42??) bedevil the passers the most. More things to think about. |
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Post by mikegarrison on Jul 15, 2021 0:41:05 GMT -5
No No No! This equal time assumption is wrong. What he is describing is correct, but for the wrong reason.
I see I also commented on he article at the time. Looking at my comment, I'm not so sure I was correct as I thought I was four years ago. I still think there are problems in his description of what happens and why it happens, though.
No one disputes that the drag suddenly drops as the speed increases. This drag crisis is measured data. His explanation of why it happens still seems wrong to me.
The other thing that isn't addressed here is that this is not symmetric with the direction of the Reynolds number change. In other words, the drag crisis happens at a different point when the ball is slowing down than it would happen if it is speeding up. But in general, of course it is going to be slowing down, so I'm pretty sure it was tested that way.
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Post by ay2013 on Jul 15, 2021 2:44:51 GMT -5
would love to see a link of your daughter's highlights. Sounds like she's a beast for sure. I appreciate that, but I do not use this forum to promote my daughter. Anonymity and all =) Taking everything you’ve said as fact (a U18 girl is blasting float serves at the very top end of the physical spectrum with enough accuracy to rack up dozens of aces in one weekend), I have a hard time believing you’d stay “anonymous” on this forum. |
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Post by silverchloride on Jul 19, 2021 13:28:57 GMT -5
I appreciate that, but I do not use this forum to promote my daughter. Anonymity and all =) Taking everything you’ve said as fact (a U18 girl is blasting float serves at the very top end of the physical spectrum with enough accuracy to rack up dozens of aces in one weekend), I have a hard time believing you’d stay “anonymous” on this forum. I'll never tell =) |
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