Lift Bernoulli

SaintJude · Mar 19, 2012

Imagine a golf ball traveling in semi-turbulent air. As the ball spins forward, will the turbulent flow it experiences lift the ball?

Do most objections moving in semi-turbulent fluid (like an airplane in air) experience "lift"?

thais · Mar 19, 2012

SaintJude said:
Imagine a golf ball traveling in semi-turbulent air. As the ball spins forward, will the turbulent flow it experiences lift the ball?

Do most objections moving in semi-turbulent fluid (like an airplane in air) experience "lift"?

I thought only laminar flow was in the MCAT ?

typicalindian · Mar 19, 2012

"spin forward" you mean like top spin? Top spin makes it dip downward where as backspin makes it lift up. Im not sure if I understood your question but hopefully my answer helped. If you've ever played tennis you should be able to relate the effect of spin on the ball very easily.

As for airplanes, the way they experience "lift" is because they have a larger surface area above the wings than below. This causes the air above the wings to move faster to keep up wit the air below which causes the pressure above the wing to decrease relative to below the wing, which leads to the plane "lifting up"

MedPR · Mar 19, 2012

SaintJude said:
Imagine a golf ball traveling in semi-turbulent air. As the ball spins forward, will the turbulent flow it experiences lift the ball?

Do most objections moving in semi-turbulent fluid (like an airplane in air) experience "lift"?

I don't really know what you're asking, but I can tell you, as a golfer, than top spin reduce lift while backspin increases lift.

I think the objects in air only experience lift if the pressure on the top is less than the pressure on the bottom; like an airplane wing. I'd imagine that if you somehow flipped the wings of an airplane upside down mid-flight that the air would actually push the airplane down instead of help to lift it.

The wings are curved at the top so that air passing over it must take a longer path than the flat bottom surface of the wing. So, like in water, air takes the path of least resistance and you have more air on the bottom of the wing, thus inducing lift.

SaintJude · Mar 19, 2012

Ok, I didn't want to do this--but I'll put the darn question.

In aerodynamic design, reducing the coefficient of friction is critical to drag. Most of the time that means eliminating turbulent flow. yet pure laminar flow is not ideal. Which of the following is not a reason that a golf ball flies better w/ asymmetric dimples laid in an isometric pattern?

A. It reduces overall profile (cross-sectional area of the ball.)

B. Turbulent flow from the dimples can actually lift the ball if it spinning.

C. Asymmetric dimples raise turbulent flow.

D. Isometric patterns raise laminar flow.

Answer in white: D

C & D I understand, but what is A & B saying!!?

Edit: MedPr, You golf?! I was actually going to PM you this question, but then decided against 'cause I thought it be random...Not knowing this is your niche

typicalindian · Mar 19, 2012

SaintJude said:
Ok, I didn't want to do this--but I'll put the darn question.

In aerodynamic design, reducing the coefficient of friction is critical to drag. Most of the time that means eliminating turbulent flow. yet pure laminar flow is not ideal. Which of the following is not a reason that a golf ball flies better w/ asymmetric dimples laid in an isometric pattern?

A. It reduces overall profile (cross-sectional area of the ball.)

B. Turbulent flow from the dimples can actually lift the ball if it spinning.

C. Asymmetric dimples raise turbulent flow.

D. Isometric patterns raise laminar flow.

Answer in white: D

C & D I understand, but what is A & B saying!!?

Edit: MedPr, You golf?! I was actually going to PM you this question, but then decided against 'cause I thought it be random...Not knowing this is your niche

Why wouldn't you want to post the question? Is this some kind of secret question?

Edit: also, did my airplane and topspin/ backspin explanation make sense to you?

typicalindian · Mar 19, 2012

MedPR said:
I don't really know what you're asking, but I can tell you, as a golfer, than top spin reduce lift while backspin increases lift.

I think the objects in air only experience lift if the pressure on the top is less than the pressure on the bottom; like an airplane wing. I'd imagine that if you somehow flipped the wings of an airplane upside down mid-flight that the air would actually push the airplane down instead of help to lift it.

The wings are curved at the top so that air passing over it must take a longer path than the flat bottom surface of the wing. So, like in water, air takes the path of least resistance and you have more air on the bottom of the wing, thus inducing lift.

I'm not so sure that it's correct for you to say that. I think the key to the lift is the difference in pressure above and below the wings.

chiddler · Mar 19, 2012

The reason that there is lift when it spins backwards is because backwards spin causes more velocity on the top of the golf ball. More velocity means less pressure, right? So there's some lift associated with it.

What does semi-turbulent mean? As opposed to fully turbulent?

milski · Mar 19, 2012

Any sort of asymmetric profile will create some pressure difference which will result in some amount of lift. Asymmetric here can be any sort of lack of symmetry, including a rotation of the object. The dimples of the golf ball allow it to have that rotation be more pronounced and thus will increase the lift generated by it.

Front side of the ball spinning up will create lift up, spinning down - lift down. That's easily confirmable by different sports, some of them played by MedPR.

typicalindian is spot on with lift being difference of pressures. The difference of areas is not that important though - there are airplanes which have a fully symmetric wing. They still fly since in flight the wing is tilted slightly up on the front side, allowing for enough difference of pressure.

MedPR · Mar 19, 2012

SaintJude said:
Ok, I didn't want to do this--but I'll put the darn question.

In aerodynamic design, reducing the coefficient of friction is critical to drag. Most of the time that means eliminating turbulent flow. yet pure laminar flow is not ideal. Which of the following is not a reason that a golf ball flies better w/ asymmetric dimples laid in an isometric pattern?

A. It reduces overall profile (cross-sectional area of the ball.)

B. Turbulent flow from the dimples can actually lift the ball if it spinning.

C. Asymmetric dimples raise turbulent flow.

D. Isometric patterns raise laminar flow.

Answer in white: D

C & D I understand, but what is A & B saying!!?

Edit: MedPr, You golf?! I was actually going to PM you this question, but then decided against 'cause I thought it be random...Not knowing this is your niche

A. By reducing surface area, you reduce drag. So this is a reason, and therefore not the right answer.

B. The dimples increase turbulent flow because the air molecules must go into the dimples rather than just flowing smoothly over the surface as they would a perfectly smooth ball. Like in the wing example, the air molecules bang up against the surface of the dimpled golf ball (instead of simply sliding across it) which increases pressure and induces lift. This is a reason, and therefore not the right answer.

typicalindian said:
I'm not so sure that it's correct for you to say that. I think the key to the lift is the difference in pressure above and below the wings.

Well, more air particles passing = greater pressure because more air particles = more force and pressure is F/A.

chiddler · Mar 20, 2012

typicalindian · Mar 20, 2012

MedPR said:
A. By reducing surface area, you reduce drag. So this is a reason, and therefore not the right answer.

B. The dimples increase turbulent flow because the air molecules must go into the dimples rather than just flowing smoothly over the surface as they would a perfectly smooth ball. Like in the wing example, the air molecules bang up against the surface of the dimpled golf ball (instead of simply sliding across it) which increases pressure and induces lift. This is a reason, and therefore not the right answer.

Well, more air particles passing = greater pressure because more air particles = more force and pressure is F/A.

Right right agreed. My mistake

MedPR · Mar 20, 2012

chiddler said:

I'm going to ignore this because it confuses me

chiddler · Mar 20, 2012

MedPR said:
I'm going to ignore this because it confuses me

lol

The spin drags air with it. So as the ball is spinning, it's making a tiny wind at the bottom of the picture.

This wind crashes with the incoming wind ---> <--- and bam, no air movement.

On the other hand, the air on top is flowing quickly. Fast air is lower pressure air.

SaintJude · Mar 20, 2012

typicalindian said:
Why wouldn't you want to post the question? Is this some kind of secret question?

Edit: also, did my airplane and topspin/ backspin explanation make sense to you?

Haha--no--i was being lazy..../scared of a plethora of responses that may further confuse me. And no I didn't understand your backspin/topspin analogy.

How did you guys (MedPr) know that a reduction in surface area would reduce drag? S**** how did I miss that?

And chiddler what are you (saying/drawing??!) Mainly, how did you know the air on top is moving faster??

MedPR · Mar 20, 2012

SaintJude said:
Haha--no--i was being lazy..../scared of a plethora of responses that may further confuse me. And no I didn't understand your backspin/topspin analogy.

How did you guys (MedPr) know that a reduction in surface area would reduce drag? S**** how did I miss that?

And chiddler what are you (saying/drawing??!) Mainly, how did you know the air on top is moving faster??

Well because it is kind of intuitive. Point a pencil straight down and drop it. Then point it parallel to the ground and drop it. Which one has a greater surface area exposed to molecules contributing to air resistance? So which one experiences more drag?

chiddler · Mar 20, 2012

i drew it nicely :-3

and to repeat, more velocity = less pressure.

milski · Mar 20, 2012

chiddler said:
i drew it nicely :-3

SaintJude · Mar 20, 2012

Ah, yes of course! I remember now that I've learned that less surface area means less drag. More surface area --> more drag. This principle is what parachutes rely on!

MedPR · Mar 20, 2012

chiddler said:
i drew it nicely :-3

and to repeat, more velocity = less pressure.

Yes, I'm glad you reminded me of this because it is completely counterintuitive. Bernoulli says highest pressure horizontal pipe (or anything, I guess) = region of lowest velocity.

SaintJude · Mar 20, 2012

chiddler said:
i drew it nicely :-3

and to repeat, more velocity = less pressure.

So chiddler, thank you for drawing it out again! To summarize, you are saying that the spin forward of the ball leads to the wind currents sort of crashing into the thrust currents of the rotating ball. This causes the velocity of the air beneath the ball to be relatively less than that of air currents above the ball.

Bernoulli's principles says lower velocity--higher pressure. And since Pressure is proportional to Force, the ball will experience kind of a net pressure pointing upwards, or really a net force pointing upwards (aka lift)

?

chiddler · Mar 20, 2012

SaintJude said:
So chiddler, thank you for drawing it out again! To summarize, you are saying that the spin forward of the ball leads to the wind currents sort of crashing into the thrust currents of the rotating ball. This causes the velocity of the air beneath the ball to be relatively less than that of air currents above the ball.

Bernoulli's principles says lower velocity--higher pressure. And since Pressure is proportional to Force, the ball will experience kind of a net pressure pointing upwards, or really a net force pointing upwards (aka lift)

?

The velocity of the air above the ball is less than below...

but minor detail. all else sounds correct.

SaintJude · Mar 20, 2012

chiddler said:
The velocity of the air above the ball is less than below...

but minor detail. all else sounds correct.

Naaaah, that's can't be true. Wouldn't that entire negate your argument? The pressure is higher on the bottom & (so it's velocity is lower). You need that gradient to develop the lift force you're talking about.

Edit: In fact in your supposedly ugly picture (beautiful in my eyes) you drew that the velocity on the bottom was less than that of the top.

chiddler · Mar 20, 2012

SaintJude said:
Naaaah, that's can't be true. Wouldn't that entire negate your argument? The pressure is higher on the bottom & (so it's velocity is lower). You need that gradient to develop the lift force you're talking about.

Edit: In fact in your supposedly ugly picture (beautiful in my eyes) you drew that the velocity on the bottom was less than that of the top.

i drew them opposite on a whim. the first, gorgeous! picture that i drew was spinning backwards. the second one is spinning forwards.

so i guess it depends on which one you're referring to.

SaintJude · Mar 20, 2012

So, I'll just recap. I've never been sure that I'm cut out for medicine, but if I'm blessed with classmates as smart as you guys then there's hope!

Milski: Any sort of asymmetric profile will create some pressure difference which will result in some amount of lift. Asymmetric here can be any sort of lack of symmetry, including a rotation of the object.

Now whenever I see a problem that mentions any sort of asymmetry in the object's flight or speaks of introducing asymmetry into the object's design itself, I'll know it's to facilitate lift & optimize the object's path

As chiddler explained, the picture shows how the rotation of the ball leads to turbulent flow opposing the air currents and creates a pressure gradient (due to lower velocity below the ball's flight). This pressure gradients creates a net upward force = lift. And that's how turbulent flow from the dimples can actually lift the ball if it is spinning.

The picture also illustrates MedPr's explanation on why reducing the area of the ball reduces the drag.
The numerous air vortexes formed within the dimples will create turbulent flow. And actually expose the dimpled ball to less opposition from air (see the smaller separation as opposed to the large amount of air offering some resistance against the smooth ball.
So the smaller surface area of the dimpled ball reduces drag.

chiddler · Mar 20, 2012

wouldn't dimpling the ball create more surface area on it?

dmf2682 · Mar 23, 2012

chiddler said:
wouldn't dimpling the ball create more surface area on it?

nah, dimpling is like digging holes out of the surface. If you pimpled the surface you'd be adding heaps of stuff to the surface

Sorry to bump the thread, I was cruising the Carribbean all this week but it's my field. nice job reasoning it out

Lift Bernoulli

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