Why does a golfball fly off the clubhead at a speed greater than the clubhead speed? (Is this even true?)
Thanks in advance.
This is a good question.
This was mentioned a few days ago in this thread, and they seem to agree that yes, it does accelerate.
However, in this thread from way back, they say it doesn’t.
Some people have claimed that balls have been measured going faster than the clubhead that hit it, but I’ve never seen a cite. This would answer the question. I think it basically boils down to whether or not the ball finishes decompressing before it separates from the clubhead.
It is perfectly possible for the ball to go faster than the clubhead speed because of the conservation of momentum. It all depends upon the ratio of clubhead weight to ball weight and the velocity that is lost by the clubhead at impact.
This example is idealized in that it is assumed that the collision is perfectly elastic which isn’t true in the actual case but it does illustrate the principle.
Suppose the clubhead to ball weight (mass actually but since it is all on the surface of the earth we can use either) ratio is 10:1 and the clubhead initially goes 120 mph (176 fps) before impact and 102 mph (150 fps) after. The ball velocity will be 177 mph (260 fps). Such clubhead and ball speeds are actually achieved by expert golfers.
In this ideal case the equation is:
10176 + 0 = 10150 + x where x is ball speed. The left side is the total momentum before impact and the right side is the momentum after.
G’day
The ball can only reach any given speed if it is accelerating at all speeds lower than that speed.
The ball only accelerates when it is subject to an external force from the club head.
The club head will not exert a force on the ball while they are not in contact.
If the ball is travelling faster than the club head they will not remain in contact.
However, the edge of the ball that is in contact with the club head need not be moving at the same speed as the centre of mass of the ball.
So the ball can in theory continue to extract momentum from the club head so long as the speed of the ball minus the speed with which its deformed surface is relaxing back to its equilibrium position is great than the remaining speed of the club head AND the position of the ball is in advance of the position of the face of the club by less than half the current length of the ball.
I would be surprised if this effect was large: I’d like to hear about some actual measurements.
Regards,
Agback
ball speed = ((club head weight x 2) x club head spead) / (club head weight + ball weight)
So, the reason it can gain so much speed over clubhead is because the ball surface is round (contact point is a dome - good mechnaical properties for good forward transfer of “uncrushing” force) and it has a super resilient bounce-back-to-normal-shape material? Would that be a good summary explanation? Or does the dome not matter?
Well, in a word, no.
The ball can go faster than the club because it has less mass than the clubhead.
In the ideal case of momentum transfer as worked out in physics books the shape doesn’t matter. This is because in such ideal cases, all the objects are points and are rigid. That is, they do not deform on impact.
In the actual case shape matters, and a lot of time and money goes into designing the clubhead face so as to transfer as much momentum from clubhead to ball as is possible. Both the clubhead and the ball deform at impact and are therefore in contact for some time. Club and ball design are the subject of a lot of computer time for simulations by the manufacturers and also a lot of actual testing.
The ball is round so that it will roll. A lot of effort also goes into designing the dimple pattern which doesn’t affect momentum transfer much, if at all, but does greatly affect the flight of the ball. The object is to have a dimple pattern that provides aerodynamic lift and minimizes the drag. And nowadays the dimple patter also minimimizes the right or left curve caused by improper swings. The duffers can’t reduce their slices (right hand curve for right handed golfer) so the ball makers have tried to do it for them.
The ball cover material should be able to withstand repeated hard blows without getting cuts or dents and present materials are excellent at that. The core material should be able to deform and return to its original state with as little loss in energy as possible. And present day materials are also excellent in that regard.
Actually, both threads agree. When the ball leaves the club face, its center of mass has a higher velocity than that of the club, because the ball deforms. After losing contact with the club, the ball immediately starts to deccelerate (which was the subject of the earlier thread).
From here:
See also Golf Ball Science and Ball-Club Physics and HowStuffWorks (with animation!); the first of which makes some comments about matching the stiffness of the ball with expected club speed (which might answer your question, hauss.
Thanks everyone.
I’m trying to explain this thing in as little words as possible just for fun, so let me know if this is closer:
The ball deforms, so just before seperation of the ball and clubhead, the front portion of the ball is travelling much faster than the rear portion of the ball; this front portion’s differing speed “pulls” the posterior portion of the ball faster, increasing the balls COG speed by a fraction. (By pull, I mean, it simulates, for a split second during contact, a lighter, less massfull ball). The clubhead also deforms, so its high shape-resiliency characteristics additionally assist in propelling the ball faster than the clubhead speed. So, in short, it’s all about the materials (Club-ball) shape-resiliency and the fact that they store the extra physical energy to seemingly cheat the laws of physics.
Thanks to zut for those sites.