Golf Ball Backspin: Understanding Compression and Groove Effects

[lovethepirk]

Thanks in advance...

I am trying to conceptually get my arms around backspin placed upon a golf ball when an angled(lofted) putter strikes a ball.
-I'm assuming as you can see in the attachment that the two objects meet with the horizontal center of gravity at the same location so any twisting of the putter('gear effect' in golf) is eliminated.

When an angled object meets a ball, my education tells me there should be some ball compression and the ball should ride up the face of the putter causing the ball to rotate(backspin). The more angle(loft) the more rotation takes place.

Here is where it gets interesting. There are a lot of designs now that have grooves in the face of the putter. These grooves add to the friction of the ball and putter, hence any compression and face riding of the ball should if I am correct be greater. These groove designs are claimed to cause "overspin" vs the flat surfaced face.

I disagree with this claim. Unless a golfer strikes the golf ball with a tangent vector in an upward direction that somehow supersedes the "physics" inherent in the backspin equation. At some point the upward vector strike will cause more friction than the friction seen with the ball riding the face and thus top spin could be a reality.

Any thoughts on this, equations, etc. Thanks.

 

[A.T.]

The force at impact doesn't have to be horizontal. With zero friction it would be perpendicular to the putter surface, and thus have an upwards component, while the ball would get no spin. With friction it gets complicated and depends on the amount of friction, and the angular inertia of the ball. The amount of friction will determine the amount of backspin. But I see no way to get topspin with this geometry. Even perfect static friction would cause backspin, but not "overspin", because the ball would just roll on the surface without slippage. So both claims seem unrealistic to me.

There are many slow motion videos of such impact on the net.

 

[lovethepirk]

Thanks for the reply...can you comment on the amount of upward tangent force needed to possible apply overspin?

Similar to if you struck a ping pong ball with a tremendous amount of upward paddle motion you can apply over spin even with an angled paddle facing upward as well...at least I think this. For instance...if it was a 1:1 relationship I could see this happening...if you have 10 degrees of putter angle and 10 degrees of upward tangent force at impact you get zero spin. 10 degrees of angle and 11 degrees of tangent force you now get topsin.

 

[A.T.]

... the amount of upward tangent force needed to possible apply overspin... 11 degrees of tangent force you now get topspin.

You seem to think, that you can control this forces by frictional parameters to achieve any spin you want. I don't think this is the case.

Consider the reference frame of the putter, and it gets similar to throwing a non-spinning golf ball against a stationary surface (floor or a wall). Note that topspin along the stationary surface corresponds to backspin in the putter case, and vice-versa.

It's hard to see how you can get what would be a topspin in the putter case here. The same for back overspin in the putter case. Unless the overspin comes from the fact the the putter slows down on impact.

 

[lovethepirk]

Thanks for the comments. I am not sure what to think...I completely agree with you that physics simply explains backspin should exists, but I am not sure if you can overcome this backspin.

Have a look at the attachment. If the dotted line is your path of strike, and the coefficient of friction b/w the surfaces creates certain speeds of rotation depending on the angle of the putter than I would tend to think that an "Upward Strike" as seen in the attachment must alter this rotation to some degree.

My question is this altering only the backspin or can the upward strike now cause friction in the other direction and hence cause overspin.

 

[A.T.]

I would tend to think that an "Upward Strike" as seen in the attachment must alter this rotation to some degree.

Sure, that "Upward Strike" is a different case. But I doubt it can be executed with a lot of speed. You can also hit just the top of the ball with the putter's lower edge to get topspin.

 

[lovethepirk]

That is what I am trying to decipher...how much upward strike do you need?

You seem to imply that it is a force issue only when I think that it is a striking angle issue along with a force issue...perhaps maybe even an acceleration issue more so.

Given a specific coefficient of friction is there anyway to mathematically decipher this? I can handle difficult math.

I've seen some friction equations and they are confusing to me as they start getting into weight and such...before I start twisting my brain I'd like to find guidance on here.

Thanks.

 

[A.T.]

That is what I am trying to decipher...how much upward strike do you need?

To get get topspin by hitting with the putter's surface (not an edge)? The putter velocity vector must have more angle from the ground, than the putter's surface is tilted backwards from the vertical.

 

[lovethepirk]

That was my initial assumption...but going back to my original post...what does a grooved face surface do to this equation?

On one had grooves increase coefficient of friction so I see more backspin, but as you apply upward force that increase in friction then helps it more quickly create topspin.

If you are saying that the angle of the putter and angle of force is a 1:1 equation...then does that equation change when you add grooves or roughen up the face of the putter to cause increased coefficient of friction?

 

[A.T.]

...what does a grooved face surface do to this equation?

Increasing friction coefficients alone doesn't change the direction of the spin, just its magnitude. The question is, if there really is so much slippage without those grooves, that it matters.

 

[lovethepirk]

I'm not sure I am being clear...we are going in circles. Here is an example

1) A professional strikes a ball with a flat face, horizontal force , and 3 degrees of angle. The ball rides the face and causes 10 rpms of backspin.
-imagine now a 'grooved face' or a 'more friction' face and same input values...The ball rides the face and causes 20 rpms of backspin.

*****the grooves or increase in friction causes more backspin...simple physics.

Now we want to eliminate backspin...it is the enemy!

We suggest that our professional apply an UPWARD tangent force vector on the ball to attain TOP SPIN.

2) At a 10 degree UPWARD force is he better served using a smooth face or sand paper like face to MAXIMIZE top spin?

 

[A.T.]

We suggest that our professional apply an UPWARD tangent force vector on the ball to attain TOP SPIN.

Can he realistically do this?

At a 10 degree UPWARD force is he better served using a smooth face or sand paper like face to MAXIMIZE top spin?

If he achieves topspin with the smooth face, then increasing friction will give him more topspin.
If he achieves backspin with the smooth face, then increasing friction will give him more backspin.

 

[lovethepirk]

Gotcha...I got it now...if the tangent force is perfectly perpendicular to the angle of the face there would be no spin. When the tangent strike angle deviates from being perpendicular either way, you get either back or top spin. Thanks for the discussion.