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Associate

Join Date: Feb 2009
Location: India
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### In Which Case the Friction is Higher?

03/29/2012 11:26 PM

In which case the friction is higher ??

A steady ball travelling in air or A spinning ball travelling in air ?

to my knowledge i suppose frictional resistance is higher on steady ball as we know that static friction is higher than rolling friction.

But i'm confused over it because additional axis of motion should add to resistance so spinning ball should under go more friction than a stead ball.

can anyone plz explain me in detail by going into the subject ??

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Guru

Join Date: Oct 2008
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#1

### Re: In which case the friction is higher?

03/29/2012 11:55 PM

Is the air still, or moving, relative to the direction of travel of the ball?

How is the ball spinning, relative to the direction of travel of the ball?

Are you discounting other forces that would act on the ball under these conditions?

I think your question is ambiguous.

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Guru

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#3

### Re: In which case the friction is higher?

03/30/2012 12:53 AM

Homework. Don't know. Don't care.

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Associate

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#8

### Re: In which case the friction is higher?

03/30/2012 1:21 PM

i just tried to keep my questions short so it turned out to be ambiguous.. excuse me !

i'm grateful to ur response !

1. Air is "still" relative to the direction of travel of the ball.
2. the ball spinning "Perpendicular" to the direction of travel of the ball
3. If other forces effects the velocity of the ball more than the air resistance and surface friction, then i would like them to be considered
• assumptions on a smooth surfaced ball like cue ball
• velocity of the ball is constant and travelling in still air

if i missed to give any details required plz let me know..

thank you sir

Guru

Join Date: Oct 2008
Location: 34° 34' 21.60" N, 92° 55' 42.28" W
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#9

### Re: In which case the friction is higher?

03/30/2012 2:26 PM

Consider how a spinning , smooth sphere will travel in a vacuum.

Will it goe in a straight line or curve as a result of rotation about its own axis?

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Associate

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#11

### Re: In which case the friction is higher?

03/31/2012 12:54 AM

thank you...

Associate

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#15

### Re: In which case the friction is higher?

03/31/2012 12:18 PM

please sir.. help me out !

Guru

Join Date: Mar 2007
Location: City of Light
Posts: 3311
#16

### Re: In which case the friction is higher?

04/01/2012 9:10 AM

I shall give you a hint: make the model of each movement separate and then try to build up their "sum".

What you should know is that depending on the Reynolds number and the relative rotation velocity the ball can have a helicoïdal trajectory. This is known to happen in water in air it is less probable.

Guru

Join Date: Sep 2007
Location: Japan
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#2

### Re: In which case the friction is higher?

03/30/2012 12:17 AM

play golf! and find out!

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Guru

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#4

### Re: In which case the friction is higher?

03/30/2012 2:31 AM

Friction would be associated with air speed, so the question becomes, is the surface of a ball accelerated by spin...

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Associate

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#12

### Re: In which case the friction is higher?

03/31/2012 1:10 AM

yes.. the ball is set to be spinning at constant speed by external source.

th ball follows a straight line at a defined velocity through out its journey.

can you please provide me formula particularly for friction on the surface when th conditions are as shown in the figure below

Guru

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#13

### Re: In which case the friction is higher?

03/31/2012 4:56 AM

It is a home work according to your last messages!

CR4 does NOT make home work ONLY helps after the student aleady made an effort.

Think what could happen and then after you put on line your reszults we can help.

Associate

Join Date: Feb 2009
Location: India
Posts: 34
#14

### Re: In which case the friction is higher?

03/31/2012 5:20 AM

no its not an home work question. i'm exploring my mind.... i have tried it simulating on Ansys software but my idea need some mathematical back up to import it into FLUENT software where i can show picture of what i was trying to prove.

i need to put those formulas in C language so that it will synchronize that data and give me accurate results...

if i don't get those mathematical inputs my simulation work will b just a kind of animated movie which doesn't obey any physics !

so please help me out ! by the way i finished my graduation 3years back now i'm working in local CAD training center for 10k INR (i.e \$200 /per month.)

thank you !

Guru

Join Date: May 2007
Location: Harlow England
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#5

### Re: In which case the friction is higher?

03/30/2012 3:07 AM

I'm sure Google will show tons of stuff explaining the swerving of spinning balls in flight.

Try 'physics of curve ball' the stuff starts coming up before you even finish typing curve...
I just tried, but I'll let you do it yourself.
Del

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Guru

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#6

### Re: In which case the friction is higher?

03/30/2012 6:34 AM

You lazy......

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Guru

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#7

### Re: In Which Case the Friction is Higher?

03/30/2012 8:08 AM

In air you should make clear if you mean the air resistance or only the ball friction since those are different. The air resistance is more than the friction alone.

Friction is due to only shear of layers near to the ball surface, resistance covers also the fact that air is displaced by the ball an has to change direction so othe forces are involved.

2
Guru

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#10

### Re: In Which Case the Friction is Higher?

03/30/2012 5:22 PM

A ball moving through air that is initially non-spinning will likely begin to spin as it interacts with air. For it not to begin to spin would require equally balance drag all over the ball at all times, and that just doesn't seem likely.

What has a greater effect is the surface of the ball. It is well known that a dimpled golf ball travels farther and straighter than an equivalent smooth ball. The structure of the dimples takes into account the fact that the ball is spinning to help the ball go farther.

From Wikipedia, aerodynamics of a golf ball:

When a golf ball is hit, the impact, which lasts less than a millisecond, determines the ball's velocity, launch angle and spin rate, all of which influence its trajectory (and its behavior when it hits the ground).

A ball moving through air experiences two major aerodynamic forces, lift and drag. Dimpled balls fly farther than non-dimpled balls due to the combination of two effects:

First, the dimples on the surface of a golf ball cause the boundary layer on the upstream side of the ball to transition from laminar to turbulent. The turbulent boundary layer is able to remain attached to the surface of the ball much longer than a laminar boundary and so creates a narrower, low pressure, wake and hence less pressure drag. The reduction in pressure drag causes the ball to travel farther.[7]

Second, backspin generates lift by deforming the airflow around the ball,[8] in a similar manner to an airplane wing. This is called the Magnus effect. Backspin is imparted in almost every shot due to the golf club's loft (i.e., angle between the clubface and a vertical plane). A backspinning ball experiences an upward lift force which makes it fly higher and longer than a ball without spin. (see Baez[9]) Sidespin occurs when the clubface is not aligned perpendicularly to the direction of swing, leading to a lift force that makes the ball curve to one side or the other. Unfortunately the dimples magnify this effect as well as the more desirable upward lift derived from pure backspin. (Some dimple designs are claimed to reduce sidespin effects.)

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