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Name: Bruce
Status: student
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Question:
I am not a teacher (was before) but the answer to this question would seem to be worthwhile to Newtonian students. I manufacture golf clubs and have observed a phenomenon I can not explain. Traditional golf club heads were made of real wood. They weighed about 200 grams and were about 250 cc's in volume. Now, given the use of metal golf heads, they still weigh about 200 grams but they are as large as 450cc's. The mass seems to be the same but it is more widely distributed (less concentrated). Does the diffusion of mass over a wider plane, even though the object weighs the same, change the transfer of energy scenario? In addition, I manufacture a head made of ceramix composite, which looks and sounds like persimmon woods. You can see the head at www.caldwellgolf.com. The walls of the head are thick, somewhat like persimmon wooden heads. The ceramix heads weigh about 200 grams and the volume of the head is 265cc's. Robotic tests, where a golf ball is struck under identical conditions, indicate that the spin rate generated by a larger cc's metal golf head accelerates as swing speed increases and with the ceramix head, the opposite is true. As swing speed increases, spin rates decrease. In golf, lower spin rates for a ball hit off the tee, is a good thing. How do I explain the fact that our spin rates go down while metal heads cause increased spin rates. Does the answer have anything to do with the concentration of mass? Does the malleability of the material (Wooden heads, "give" on impact and so do ceramix heads),have anything to do with the spin rate differences?



Replies:
Bruce,

I am not a golf expert, nor a physics expert, but I might know enough to hazard an educated guess. From what I know of golf clubs, the main component that is important in hitting the ball is the club's front surface. Everything behind the face that makes contact with the ball is for aerodynamics and maintaining a center of mass. I would say that the main difference in how the surface material differs in how it hits the ball might be due to one of two factors. As I said, this I do not know this for sure, but I would think it might be due to either how the hardness of the material (not malleability) affected the frictional impact as far as angular momentum transfer. In this spirit, another thing that might affect angular momentum is where the center of mass is located. A larger volume head allows for a center of mass further back from the face of the club and might impart more or less spin depending on whether the center is located near the top or bottom behind the face of the club.

Matt Voss


Bruce,

The physics of hitting a golf ball are remarkably complex. The materials science of the golf club and ball combined with the fluid mechanics of the flying ball are all extremely complicated. Major golf companies invest millions of dollars to understand why equipment behaves the way it does, and trying to optimize it's performance. I will provide some generalities here, but there are many, many important factors involved beyond what can be covered in this forum.

As I think you know, the main factors that determine the length and trajectory of a golf ball are its initial speed, its launch angle, and its spin rate. However, it is not correct to say that lower spin is always better. The spin you seek depends on weather conditions, ground conditions, and the type of shot you are trying to hit (more carry versus more overall distance). Those values are different for different swing speeds. Most pro shops have charts that list these ranges, which I'm sure you know. However, these are just general guidelines -- nothing matches actual on-course (or on-range) data.

Robot data is also not quite the 'proof' you might think it is. Robots can be set up to make one club appear superior to another (a fact that's well known, and well used, among clubmakers). The interaction between the swing and the physics of the club and golf ball is very complex -- with one swing, one club may seem superior, but with another swing, another club may seem superior. To really understand the interaction between the swing, club, ball, and conditions, pros (and increasingly amateurs) spend a great deal of time hitting balls with multiple clubs and use high speed cameras to find the exact club, shaft, and ball that fits their swing.

Regarding your club, I would recommend you sit down with a materials engineer or physicist to understand your material. There are many kinds of ceramics, so I'm not sure exactly what you are using -- and the exact properties of the material make a big difference. The geometry of your club and club face also are very important. The main factors that affect ball speed and spin are the coefficient of restitution (how much of the energy of the club head is transferred to the ball), the amount of time the ball spends on the club face, and vector of the club head/face path relative to the ball. During impact, the club face deforms slightly, and then rebounds. The nature of the deformation and rebound along with the deformation of the ball governs how efficiently energy is transferred, and how much spin is imparted. And, we haven't even gotten to how performance differs when you hit the ball off the center of the club face (in fact much of the reason for deep-faced clubs is to improve off-center hits).

So having said all this, there are many possible reasons for your club's lower spin rate. Without having specific data on your club's materials and geometry, along with swing data, any explanation would be purely speculative (and more than likely not correct). My best advice is to work with a person who can break down the physics for you so that you can generate and analyze your data more accurately.

Hope this helps,

Burr



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