Quote:
Originally Posted by Mox  Like I said - further debate would likely be pointless, but still ... 
Bill, Yes - you CAN (and DO) apply forces in a direction into the ground. The wedge shape of the club does not change that. The MOTION of the wedge shape is relevant, and being downward as well as forward, it applies forces in both directions. Putting a static club head next to a ball is completely irrelevant. The club head MOVES at the time of impact, and during the time the ball is compressed. It moves forwards and DOWNWARDS.
Get a soccer ball. Put it on the ground. Place one finger on top of the ball (not necessary if you have 5000fps eyesight). Put your other hand - in a wedge shape - behind the ball, below the equator. Press directly forward. Will the ball slide? Yes - quite easily.
Now do the same, but instead of pushing directly forward with the "wedge hand", now press forward as well as downward. Will the ball slide? Yes it will. Just as easily? Not it won't! Why? Because the downward forces you apply to the ball is causing increased friction between the ball and the ground.
Try it with a balloon, you will easily see it compress into the ground.
The forces are there, and they are more than marginal.
Read bullet #3 here Greg Norman has some feelings about this.
Short Game guru Dave Pelz:
That last article is actually a very good answer to the original question in this topic.
Oh - and for golfingguy - I don't think anybody is talking about distance. It's purely about spin-rate.
I choose to believe the combined knowledge of Tiger, Greg Norman, Dave Pelz and my high school physics teacher.  |
Mox,
You are creating questionable statements to support an incorrect theory. Come on now, do you really believe the ball gets compressed between the tee and clubface in a way that can contribute to velocity and spin? The ball meets the face at force of around 2500 pounds
I agree that many eminent golfers claim that the ball gets trapped with the turf and that is how spin is generated but they are wrong, these people are not speaking from scientific experimentation they are talking of what it feels like, I am not convinced your school physics teacher ever studied club/ball ballistics either.
The tremendous forces created when the lofted clubface meets the ball pushes it backwards and upwards not downwards, how can soft earth and grass compress a golf ball that is struck with these forces. Take a golf ball and see if you can compress it in your hands, try it in a vice, it is very hard and does not compress easily, dirt has no chance.
Here is an excerpt again from Mt Tutelman's site that explains and he knows a bit about golf:
- Impact lasts no more than a half millisecond.
- The clubhead moves less than an inch during this time.
- The force between clubhead and ball can peak between 2000 and 3000 pounds. (It can average about 1900 pounds over the 0.4 millisec of impact. The peak is between 1.4 and 2 times the average force.)
So what is actually going on during that half-millisecond or so of impact? Here's the story, as described by
Cochran & Stobbs -- and in somewhat more detail by
Gobush:
- In the first microsecond of impact, we have the irresistable force meeting the immovable object. The ball has to react somehow to the momentum of the clubhead, and the least-energy way it can react is by moving up the lofted clubface. Initially it slides up the clubface, because there isn't enough friction yet between clubface and ball. But all that is about to change very quickly.
- The ball cannot acclerate to an upwards velocity in no time at all; that would require infinite acceleration, which requires infinite force. So it can't get completely out of the way of the clubhead just by sliding upwards. It begins to compress on the clubface, which creates a force between the clubface and the ball. If you don't think this is a large force, just try to compress a golf ball by 30% of its diameter using your fingers. Not even close! OK, use a vise; it's still very hard to apply that much compression force. Remember, this is a force that averages almost 2000 pounds during impact, and can easily peak around 3000 pounds. This force of compression does two important things:
- It begins to accelerate the ball with a horizontal component, not just the vertical motion up the clubface.
- It creates a lot of friction between ball and clubface. So, instead of sliding up the clubface, the ball begins to roll instead.
- The ball continues accelerating upwards (due to the loft) and horizontally (due to the compressive force). The sliding has turned completely into roll, so the upwards acceleration increases the speed of roll. At some point, the momentum absorbed from the clubhead through acceleration has the ball moving faster than the clubhead. In other words, the elastic rebound of the ball's acceleration allows the ball to release from the clubhead. At this instant, its launch conditions are determined.