Ball Actually "Pinched" Against Ground or Not

[Augusta Hacker]

And one more......

www.thegolfexpert.com/articles-do_you_hit_down.php

[sacm3bill]

And one more......

Notably from that link: "The face of the club will then contact the surface of the golf ball just prior to reaching the bottom of the swing arc. As a result the ball becomes trapped between the descending clubface and the ground."

Although, I predict that statement will be dismissed out-of-hand by the powers that be as incorrect.

[Augusta Hacker]

Notably from that link: "The face of the club will then contact the surface of the golf ball just prior to reaching the bottom of the swing arc. As a result the ball becomes trapped between the descending clubface and the ground."

Utlimately, I think we all agree that the ball should be struck PRIOR to the club reaching the bottom of the swing arc......the physics then takes care of itself.

[sacm3bill]

Utlimately, I think we all agree that the ball should be struck PRIOR to the club reaching the bottom of the swing arc......the physics then takes care of itself.

Certainly, I agree with that. I don't think the issue has ever been whether the blow is descending or not.

Thanks for the links.

[ITgolfHack]

Both sides are right.....and both are wrong. I look at it as being similar to striking a pool cue....a downward blow creates the backspin (english) to create backward spin.

Generally in Pool or Billiards, if you are striking down on the ball trying to impart backspin, it's because you are in a funky position and are forced to do it. FWIW, in cue sports, english is left/right side spin, backspin is draw, and top spin is referred to as follow. Draw is applied by dropping the cue below the equator of the cue ball and striking the cue ball with as level a stroke as possible. Again, it's an example of what you feel isn't what is really happening and many beginning pool players believe that the way they get backspin is by elevating the butt of the cue.

The same thing is happening with the iron and ball. This is very easy to prove to yourself. 1. Draw side view of a golf ball sitting on the ground. 2. draw a straight light line at about a 60 to 70 degree angle to the ground right behind the ball, this is the club head. 3. now draw a vertical shaft from the angled club head. Notice that no matter where you draw the club (assuming you keep the same angle between the shaft and head), the only way the club head could make first contact with the ball above the equator is if the very bottom of the club hit the ball first, which would clearly result in a topped ball, or if the shaft of the club was nearly parallel to the ground, a near physical impossibility if you have anything that looks like a golf swing.

[powerfade]

Notably from that link: "The face of the club will then contact the surface of the golf ball just prior to reaching the bottom of the swing arc. As a result the ball becomes trapped between the descending clubface and the ground."

Are you talking about a firm pinch where the ground actually affects spin, ball flight, etc., or just an incidental pinch caused by virtue of the fact that the ball is already touching the grass?

[sacm3bill]

...the only way the club head could make first contact with the ball above the equator is...

I'm not sure why that's relevant - I don't think anyone has claimed that the ball is contacted above the equator. That driver video I posted shows that downward deformation happens even with below-the-equator contact.

Are you talking about a firm pinch where the ground actually affects spin, ball flight, etc., or just an incidental pinch caused by virtue of the fact that the ball is already touching the grass?

I can't speak to what the author of that statement is really saying - either way it's just another example of a source talking about pinching/trapping the ball against the ground. And, either way I don't think it proves or disproves either party's position - first, you can't believe everything you read on the internet, and second, obviously a "pinch" between the club and ground is not necessary for a golf shot because you can tee up an iron.

What I've been saying though is that I do think spin and ball flight can be different depending on whether the ball is sitting on a tee or on the ground, because the ground offers more resistance to the vertical deformation that occurs before the ball rises up. I have no probem admitting the possibility that there is no such difference, am just trying to understand what evidence exists one way or the other.

[iacas]

Is the ball pinched between the ground and club face? It simply has to based on physics.

No, it won't. You're simply wrong. The loft on the clubhead sends ball immediately up and away from the ground. Was even true with a 1-iron. Pros hit down on the ball with clubs that have more loft (short irons). With the long irons, a more sweeping blow is needed.

If you swing down and/or de-lofted the clubface so much that you actually had negative loft on the clubface at impact, yep, the ball would go into the ground. This would be a "very bad shot." For anything remotely acceptable, the ball immediately moves AWAY from the ground. It "rolls" up the clubface slightly, too (that's backspin). You guys are like the people who don't think the plane takes off from the treadmill.

At impact, the ball is caught between a rock and a hard place so to speak......the only direction it can go is up the club face.

Wrong. It's not "caught" at all - it's "lifted" by the loft.

Imagine hitting the ball without any resistance from the ground.....based on the downward blow.....it would move downward.

Only if the club had either no loft or negative loft would that be true. Wrong.

Are you really claiming that you can tell whether or not there's any ball deformation in those iron impact videos that have been posted?

Yep. Plus I know science.

Sigh. Once again: I *never* said the ball, or even the center of gravity of the ball, ever moves downwards. Just that there is a downward deformation of the ball that is providing a force vector against the ground.

Wrong. The ball has already moved up away from the ground so much that any deformation (less and less the more loft you add and the slower you swing - and your clubhead speed is slower with shorter shafted, heavier clubs than it will ever be with the driver) will not go below the original "bottom" of the golf ball.

Whenever someone has refuted that, their argumenent has always been "Oh, just ignore that", or "It's not as much with an iron as with a driver like in the video you posted", or "The impact conditions from a shot with a driver *can* be different than that with irons", with no data or sources or video to back it up.

Quite frankly, nobody's seen a reason to post a ton of video or "proof" because it's pretty much common sense. Again, I feel like you're saying the airplane won't take off because the wheels will spin in place.

Yeah, with YOU being the establishment in this case because it's your forum, but other than your say-so what sources can you provide or link to that support your position?

Common sense. Science. Having talked with club designers. Experience.

The degree of deformation may change with different clubs, but the physics of impact don't.

That doesn't even make sense. Of course the physics change because loft, clubhead speed, etc. changes.

FACT: A descending blow would then create downward force against the ground thus creating the "pinch".

Opinion: You seem to be ignoring the fact that clubs have LOFT.

The backspin is what in fact creates the trajectory of the ball and the amount of backspin (trajectory) is based on the loft of the club.

Huh? The backspin determines the trajectory? No.

Both sides are right.....and both are wrong. I look at it as being similar to striking a pool cue....a downward blow creates the backspin (english) to create backward spin.

The pool ball doesn't deform "into" the cloth. You've used an example that disproves your theory. Furthermore, you don't strike "downward" on a pool ball to put backspin on it - you strike near to horizontal through the ball below the equator.

(Note: I'm ignoring the fact that, since the bumper of a pool table is always above the equator of the pool balls, nearly EVERY pool shot is struck with a slightly descending blow.)

Generally in Pool or Billiards, if you are striking down on the ball trying to impart backspin, it's because you are in a funky position and are forced to do it. FWIW, in cue sports, english is left/right side spin, backspin is draw, and top spin is referred to as follow. Draw is applied by dropping the cue below the equator of the cue ball and striking the cue ball with as level a stroke as possible. Again, it's an example of what you feel isn't what is really happening and many beginning pool players believe that the way they get backspin is by elevating the butt of the cue.

Well put.

This thread is silly.

[iacas]

I'm not contributing further to this thread, btw, so respond to me all you like but you'll be doing so in vain. I won't be baited.

[m11]

i havent really read this entire argument besides the last few posts...but its unbelievable to think that the ball physically gets pinched between the clubface and the ground. That is impossible with a lofted club. Like iacas said a dozen times, you'd need negative loft to do that.

Every time a clubface properly comes in contact with a golf ball....the golfball immediately rolls up the clubface.

I will concede that it does feel like you are pinching the ball into the ground...and yes..all the golf tips advise to "pinch" the ball...but that simply refers to what you want to be feeling....from a physics stand point...its simply impossible.

[m11]

its moot for me to repeat what iacas had been saying.

but i'll just reiterate that although the feeling is of trapping the ball..and that is what the pro's say they do...and its the same thing that is advised in all golf publishings....

...but its physically impossible for a lofted club that properly strikes a ball to pinch it into the ground---the ball immediately travels up the clubface.

[ITgolfHack]

[QUOTE=ITgolfHack;187033]

I'm not sure why that's relevant - I don't think anyone has claimed that the ball is contacted above the equator. That driver video I posted shows that downward deformation happens even with below-the-equator contact.

This is relevant because the pinching concept REQUIRES a significant downward force on the golf ball. Any impact, regardless of the angle, that strikes below the equator will not put any kind of significant downward force on the golf ball (i.e. drive it into the ground). Could someone who knows a bit about physics please post a force diagram of the golf ball at the moment of impact and show me how the ground could possibly aid in imparting backspin on the ball? I really want to see how someone who understands physics could go along with this pinching concept.

If you agree that the initial contact point of the club on the golf ball is below or at the equator, then your theory is already sunk as any downward deformation of the golf ball strike the club face and not the ground. Given an angled face, if the ball deforms enough, guess what will be below the golf ball at the moment of impact, the lower face of the club head. As to the concept of the ground imparting the spin, this couldn’t be easier to disprove. 1.The golf ball is on the ground, this is a fact, it can not be argued. 2.The club is going to be moving forward toward the target at the same time it is moving down at the ball, this can not be argued. 3.The golf ball is going to be moving forward toward the target; this can also not be argued. 4.even if the ball is somehow also being driven into the ground, it will still have a much larger horizontal component to it’s velocity 5.The ball is going to be moving forward, the ground is going to be stationary, again, can’t be argued. 6.if you are standing behind a golfer and he makes his swing and the ball begins moving forward, the ground, if it was in contact with the golf ball more then an instant after impact, the friction of the ground against the forward motion of the ball, would impart a counter clockwise rotation on the ball (forward spin) If you know anything at all about physics, you will also have to agree that this can not be argued. If anyone wants to debate numbers 1 – 6 we can get into the math tomorrow when I have time. If you agree with points 1 – 6 you have to agree that the only thing that could impart backspin on the ball is the club face and that the less contact with the ground, the more backspin the club will be able to impart.

[NM Golf]

I can't believe this thread has so many posts on it. Isn't it evident that the golf ball is not pinched. Erik and the others even have video evidence. I myself use the word "pinch" to describe the feeling of crisply striking a wedge shot in order to impart spin, but its the feeling it gives, not what is actually happening.

[ITgolfHack]

And one more......

I'm a complete novice at this game myself, but what this article is talking about is that because the club face is at an angle, you can hit better and more consistent shots by delofting the club and allowing the club to strike the ground after impact or at impact, i.e. keeping the hands in front of the club head. In order to strike down on the ball, the club face MUST strike the ball above the equator of the ball, this is the ONLY way that a downward force can be imparted to the golf ball.

1.Draw a picture of a sideways view of a golf ball sitting on the ground. 2.Now draw the angled club face striking the ball above the equator 3.Now draw the shaft of the club and explain to me how you would ever get yourself in a position where the club shaft could obtain that angle to the ground.

[ITgolfHack]

I can't believe this thread has so many posts on it. Isn't it evident that the golf ball is not pinched. Erik and the others even have video evidence. I myself use the word "pinch" to describe the feeling of crisply striking a wedge shot in order to impart spin, but its the feeling it gives, not what is actually happening.

I just discovered this concept of trying to pinch the ball and it has helped my iron game tremendously, even though I know that pinching the ball is a physical impossibility.

I enjoy arguing about this because it helps my reasoning skills. I can also see where they are making their mistaken assumption and if I can just get them to see it; they will likely become better golfers in the long run because they will understand what is really happening.

[Augusta Hacker]

I'm a complete novice at this game myself, but what this article is talking about is that because the club face is at an angle, you can hit better and more consistent shots by delofting the club and allowing the club to strike the ground after impact or at impact, i.e. keeping the hands in front of the club head. In order to strike down on the ball, the club face MUST strike the ball above the equator of the ball, this is the ONLY way that a downward force can be imparted to the golf ball.

The quote I want you to read is "

As a result the ball becomes trapped between the descending clubface and the ground. The ball compresses. Because the face of the clubhead is lofted, the ball will - rather than be driven into the ground as a downward hit might imply - spin backwards up the clubface, decompresses (adding energy to its escape) and climb into the air. " This quote is not from a hack like myself but from an instructor. I guess he is just implying that it gets trapped to teach?

[Augusta Hacker]

Please see this force diagram .

Based on this illustration, you can see that the force vector imparted on the ball by the club face from the descending portion of the swing arc. From this vector, we can tell there is a downward vector (y-axis) and forward vector (x-axis) that comprises the total force vector. The forward vector does not receive significant resistance (only static friction of the ground surface and air resistance) however the downward vector will receive resistance in the form of the ground surface. If we look at this moment of impact (prior to leaving club face), we can eliminate the affect of the loft as it relates to trajectory and describe what is happening to the ball at this milli-second of time in the golf swing.

The diagram shows that there has to be a downward force that is counteracted by the ground based on Newton's Third Law of Motion....for every action, there is an equal and opposite reaction. Based on this principle, the ground has to impart force back on the ball at this moment in time on the y-axis for Newton's Third Law to hold true and this reaction is the pinching we are talking about. The equal and opposite reaction in the x-axis is imparted to the ball in the way of flight and the direction is changed based on the club face. By applying the impulse-momentum theorem the only way there is not a force exerted downward is if the impact force vector is directly at the bottom of the swing arc making the vector horizontal and 100% on the x-axis.

Kinetics is kinetics....can't argue with that.

[iacas]

Please see this

Ha! You kind of left out a major force in your diagram. You know, the one that actually gets the ball airborn due to the loft on the clubface.

My goodness. If you think those are the only forces in play, it's a wonder you ever get the ball airborn. That forward force, combined with the loft on the clubface, is what gets the ball up and it is nice of you to completely ignore it. You forgot to translate the forward force component into a normal force off the clubhead. A significant portion of that force, due to the loft, would then become an UPWARDS force.

If we look at this moment of impact (prior to leaving club face), we can eliminate the affect of the loft as it relates to trajectory and describe what is happening to the ball at this milli-second of time in the golf swing.

We can eliminate the affect of loft ??? Or we could talk about reality in which loft plays an crucial role in, you know, getting the ball airborn. Additionally, your diagram isn't to proportion - most pros hit with a descending blow of about 4-8 degrees. The forward force vector - which you then translate to loft via the normal force applied by the clubhead - is much, much greater. Then you multiply the already weak downward force by the frictional coefficients and it's lowered even more. This puts your diagram severely out of proportion: the downward force is much smaller than you've indicated, and is shrunk significantly by the relatively weak coefficient of friction between urethane and steel. Even more so if you're using surlyn, the clubface isn't perfectly clean, there's a little dew, etc. It's orders of magnitude smaller than what becomes the normal force between the clubhead and ball, and much, much, much, much smaller than the upwards component of that normal force.

The diagram shows that there has to be a downward force that is counteracted by the ground based on Newton's Third Law of Motion....for every action, there is an equal and opposite reaction.

You're going to want to take Physics 101 again.

If I set a ball on the ground, the equal and opposite reactions are gravity pushing down and the ground pushing up. They're equal and opposite, and as a result, the ball is at rest (not accelerating in any direction). If I smack the top of the ball downward, until the ball comes to rest, the forces are not equal and opposite. A ball accelerating downwards (even if it's not going to happen unless you top the ball) is not undergoing "equal and opposite" forces. Something that is accelerating (and it has to, since it starts "at rest") has, by definition, a force that's NOT counteracted equally acting on it. The ground is not perfectly hard as it would have to be to immediately "cancel" any downward force applied to it. Furthermore, given your understanding of the ground counter-acting the downward force you believe is quite large and its role in getting the ball to go up, how do you imagine a pro hits a shot in the air from the rough where the ball (and the clubhead) never even reach the ground??

Based on this principle, the ground has to impart force back on the ball at this moment in time on the y-axis for Newton's Third Law to hold true and this reaction is the pinching we are talking about.

For the many reasons I've outlined above, and several others, no.

By applying the impulse-momentum theorem the only way there is not a force exerted downward is if the impact force vector is directly at the bottom of the swing arc making the vector horizontal and 100% on the x-axis.

Yeah, and that's true in a world where you can just ignore forces, like the one that results from the LOFT of the clubhead, or where you can make other forces, like FRICTIONAL forces, appear much larger than they really are in a diagram that's severely lacking in its accuracy.