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Author Topic: Why are Tennis Balls Hairy ! ?  (Read 38633 times)

Offline neilep

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Why are Tennis Balls Hairy ! ?
« on: 25/07/2007 17:46:23 »
Hello Ball Experts,

This is a squash ball:



This is a Snooker ball:



This is a Football:



Notice how unhairy and smooth they are ?


and this is a Tennis Ball:




so...why does  a tennis Ball have a beard ?






 

Offline Karen W.

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Why are Tennis Balls Hairy ! ?
« Reply #1 on: 25/07/2007 17:53:00 »
Most likely has to do with the surface of the court and traction there on!
 

Offline JimBob

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Why are Tennis Balls Hairy ! ?
« Reply #2 on: 25/07/2007 23:43:36 »
They want to look as if they are adults

Surface area is increased. I would guess this does several things - it allows the racket to get a better grip for spin although this can be done with both squash balls and snooker balls - it will slow the ball down because of increased air turbulence - it does change other aerodynamic properties; the seams stabilize the ball

Other things are possible but it is beyond me
 

Offline kdlynn

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Why are Tennis Balls Hairy ! ?
« Reply #3 on: 26/07/2007 00:08:37 »
it cushions the blow when an out of control serve from your younger brother smacks you in the face
 

Offline kdlynn

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Why are Tennis Balls Hairy ! ?
« Reply #4 on: 26/07/2007 00:09:36 »
(partially because you weren't paying attention)
 

Offline Karen W.

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Why are Tennis Balls Hairy ! ?
« Reply #5 on: 26/07/2007 00:23:11 »
OUCH..Kadie..HEE HEE!

Jim Bob those are good points especially the slowing it down part and aerodynamics! Nice points!
 

another_someone

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Why are Tennis Balls Hairy ! ?
« Reply #6 on: 26/07/2007 01:10:33 »
They want to look as if they are adults

Surface area is increased. I would guess this does several things - it allows the racket to get a better grip for spin although this can be done with both squash balls and snooker balls - it will slow the ball down because of increased air turbulence - it does change other aerodynamic properties; the seams stabilize the ball

Other things are possible but it is beyond me

The main thing about the relationship between the ball and racket would, I imagine, be the size and elasticity of the ball.

The hair would certainly affect the boundary layer around the ball, particularly as it spins, and will increase the lift (depending on the spin imparted, lift may be other than upwards), and thus give greater control over the trajectory through spin (much the same effect as the dimples on a golf ball).
 

paul.fr

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Why are Tennis Balls Hairy ! ?
« Reply #7 on: 31/07/2007 14:42:19 »
The hair allows the ball to better interact with the air it is traveling in, the playing surface, and the racquet. Think of the difference between throwing (baseball) a fast ball and a curve ball. One would have to control the seams of the ball so that it interacts with the air differently. Same with a tennis ball. You can do a topspin or a slice or a side-spinning serveand those will be easier to impart on the ball if it has hair.
 

Offline dentstudent

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Why are Tennis Balls Hairy ! ?
« Reply #8 on: 31/07/2007 14:50:53 »
I think that also the spin is better translated into movement when the ball hits the court due to the hairs. The hairs also slow the ball down somewhat - I think that when they inspect their balls in Wimbledon, they are looking for the least fluffy ones, which will then be the fastest for the "ace" serve. (IIRC) the balls are changed every 7 games?
 

Offline lightarrow

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Why are Tennis Balls Hairy ! ?
« Reply #9 on: 01/08/2007 00:11:13 »
I think it's mostly due to avoid that the ball could slip on the racket bouncing off in "strange" ways and so to control better its trajectory (independently of spin).
« Last Edit: 01/08/2007 00:13:44 by lightarrow »
 

another_someone

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Why are Tennis Balls Hairy ! ?
« Reply #10 on: 01/08/2007 01:03:28 »
http://www.tennisserver.com/set/set_01_10.html
Quote
The tennis ball cover is rough but not like sandpaper. Looking closely at the felt you can see that air flows through those raised fabric filaments - better known as fuzz. So the surface of a tennis ball is a "porous surface." It's more like dealing with the wind blowing through leaves on a tree and just as complicated. The fuzz filaments act like tiny cylinders each having their own drag component. In addition to the skin friction drag from the cover itself, drag is created from the airflow over these fuzz fibers interacting with all the other fibers behind it. Rabi Mehta dubbed this phenomenon "fuzz drag."

Experiments Mehta conducted also showed that as the ball speed increases the fuzz filaments lay down on the ball and the fuzz drag declines. Here are two pictures from the wind tunnel test. You can see in the picture on the right that the fuzz is closer to the ball's surface. The air passing over the ball on the left is about 45 mph, while on the ball on the right the air is 135 mph.

http://www.nasa.gov/centers/ames/news/releases/2000/00_58AR.html
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Initially, we could not determine why the drag on tennis balls is so much higher than that on other sports balls, he said. "Then we realized that the 'fuzz' on the ball plays a much larger role in the aerodynamics than had been anticipated in the past," Mehta said.

"If you have a smooth ball, such as a ping pong ball, it produces a large air wake, like that of a motor boat. The ball's large wake creates drag that slows the ball's flight," Mehta said. "If you add roughness, like the dimples on a golf ball, air disturbance near the ball's surface actually helps produce a smaller air wake that creates less air drag, and the ball can go farther," he explained. A smooth golf ball might only go about 100 yards compared to the 300 yards covered by today's dimpled golf balls, he added.

"Even though a tennis ball does not have a smooth surface, you get a bigger wake because of the very rough surface, plus the effect of additional drag from each fuzz filament, which I have termed fuzz drag," he said. "Fuzz drag makes the aerodynamics of the tennis ball even more interesting since the fuzz elements change orientation with increased velocity and the fuzz wears off during play."

Mehta said the complex interactions of air density, air ‘stickiness,’ air speed and physical size and surface roughness, normally are major factors in determining how sports balls fly through the air.

Air is a bit viscous or ‘sticky,’ resulting in ‘skin-friction’ drag, he explained. When a smooth ball flies through air at a slower speed, a layer of slow-moving air forms around the ball's front. The sticky, smooth-flowing air layer separates from the ball's surface, forming a wake that begins in a circle like the edge of a grapefruit that has been sliced in half. The wake behind the smooth ball is almost as wide as the ball, creating a great deal of ‘pressure’ drag that adds to the sticky air drag on the front side of the flying ball.

Surface roughness, such as dimples on a golf ball, produce turbulence in the slow-moving air close to the ball and the more energetic layer separates much later, thus leading to a smaller wake.

"The two types of flow can easily be demonstrated at home," Mehta said. "Go to a water faucet, turn it on at a slow rate, and you get a smooth stream of water almost to the bottom of the sink. Increase the flow rate, and you get a splashy, chaotic flow; this is turbulent flow," he concluded.

http://www.princeton.edu/~asmits/Bicycle_web/sportsballs.html
Quote
Tripping the boundary layer to reduce drag on spheres is widely used in sports. For example, it is the reason why golf balls are dimpled. The dimples act like a very effective trip wire, and the reduction in drag due to the delayed separation allows the ball to travel further for the same effort. A driver shot in golf can easily make a golf ball carry 250 yards, but the same shot using a smooth ball will only carry about 100 yards. Similarly, a tennis ball has a textured surface with a convoluted seam, much like a baseball. Figure 6 shows how effective different degrees of roughness can be in reducing the drag on a sphere.
Figure 6. Drag coefficient as a function of Reynolds number for spheres with different degrees of roughness. From Munson, Young & Okiishi, Fundamentals of Fluid Mechanics, John Wiley & Sons, 1998.
 

Offline neilep

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Why are Tennis Balls Hairy ! ?
« Reply #11 on: 01/08/2007 03:00:11 »
Wow !!..Thank You....thank you all for your fantastic speculations, opinions theories and quoted texts. I really do appreciate the time taken to answer and have enjoyed reading the comments and posts. Excellent texts above George...cheers.

You have all handled my hairy balls very well !!









........................(sorry....couldn't help myself) ;D
 

Offline Karen W.

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Why are Tennis Balls Hairy ! ?
« Reply #12 on: 01/08/2007 03:42:27 »
Wow !!..Thank You....thank you all for your fantastic speculations, opinions theories and quoted texts. I really do appreciate the time taken to answer and have enjoyed reading the comments and posts. Excellent texts above George...cheers.

You have all handled my hairy balls very well !!









........................(sorry....couldn't help myself) ;D


LOL It was a good question Kind Sir with good responce and answers as well! Thanks for posing it!
 

Offline lightarrow

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Why are Tennis Balls Hairy ! ?
« Reply #13 on: 01/08/2007 18:04:59 »
http://www.tennis-supply.com/balls.htm
Quote
You will not be able to play tennis correctly if you use old tennis balls. The balls are made up of a pressurized rubber core covered in felt. When this felt becomes worn & smooth, it will not react properly when it is struck by the racquet. The ball will tend to skid when it hits the court.
 

Ethos

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Why are Tennis Balls Hairy ! ?
« Reply #14 on: 02/04/2009 21:11:47 »

You have all handled my hairy balls very well !!

I knew there was a good reason for delaying my response to this thread........................
 

Offline neilep

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Why are Tennis Balls Hairy ! ?
« Reply #15 on: 02/04/2009 23:46:31 »

You have all handled my hairy balls very well !!

I knew there was a good reason for delaying my response to this thread........................

LOL...thanks for rekindling this !  ;D ;D

(How sad am I that I find amusement in my own threads ?)
 

Ethos

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Why are Tennis Balls Hairy ! ?
« Reply #16 on: 03/04/2009 01:25:03 »

(How sad am I that I find amusement in my own threads ?)
No need for sadness neilep, we all enjoy them and so should you.
 

Offline Chemistry4me

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Why are Tennis Balls Hairy ! ?
« Reply #17 on: 03/04/2009 07:20:43 »
(How sad am I that I find amusement in my own threads ?)
At least it's only the threads! :)
 

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Why are Tennis Balls Hairy ! ?
« Reply #17 on: 03/04/2009 07:20:43 »

 

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