Year end musings

[mandrin]

Nothing is really occurring instantaneously. Even light takes a finite time to travel from A to B. Some advance that telepathic communication is perhaps instantaneous.




We probably have all experienced hearing the echo of our voice, shouting away, perhaps in the mountains, showing that it takes some time for sound waves to travel in the air.






Throwing a small pebble into a quiet lake or simple teasing the surface of a water in a bath tub one notices the waves traveling on the surface.







In general the denser the material the faster is the propagation of any disturbance in that material. The animation portrays a medium as a series of particles connected by springs. As one individual particle is disturbed, it transmits the disturbance to the next interconnected particle. This disturbance continues to be passed on to the next particle.



We are used to judge the world around us based on our senses. But we have a very limited and narrow 'window' of perception. For instance our reaction time is of the order of the down swing, i.e., 0.3 sec.

The duration of impact however is only about 0.0004 sec and is hence definitely outside our narrow 'window' of perception for the world around us. And this is precisely the reason why intuition is of no avail to solve the problem posed in the opening post. We can't readily intuitively cope with things occurring in such a very short time scale.

Let's now look at the problem at hand. Many posters have given it a try to come up with an educated guess or an intuitive opinion with also the science guys giving it a try. The crux of the matter in the problem posed is the finite time it takes for a disturbance to travel through a slender steel golf shaft.


The impact disturbance propagates through the stainless shaft and is reflected back towards the ball.

In a thin stainless steel rod a disturbance propagates with a velocity of 5000 m/s.

The steel shaft length is 1.25 m, therefore the total propagation time, to and fro, is 0.0005 sec.

Impact duration is however less, i.e., 0.0004 sec.



What a darned pity, the ball is gone and on its way before the huge mass even had a chance to give the ball even a little fair well kiss, how sad. The big mass might have been 1 kg, 10 kg, 100 kg, 1000 kg, 10000 kg, 100,000 kg, etc., it would have made no difference. The shaft has effectively decoupled the clubhead mass from the big mass. However if we had changed the mass at the other end of the shaft, i.e., m2, the clubhead mass, it would have made a difference not having to cope with the time delay due to the propagation as shown in the figure below.

There were several correct answers but Vicious Circle was the only one giving also a correct concise explanation. mjstrong starting to get close feeling bothered by the fact that I had specified the length of the shaft. For those interested to have another look at the formulas governing impact have a look my post - 'Golf Impact Physics'.

The moral of the story of my opening post is simply trying to make people a bit more aware that feeling and intuition were of no avail and should be taken with the precaution in golf swing related issues. Better and faster getting to the truth using as much as feasible science and technology as is BM's approach.

The intuitive feeling about heavy hit is and has been very strong indeed. For instance the late Homer Kelley, for one, subscribed to it. But rather incomprehensible is that the late Mindy Blake, a reputed engineer, who has lectured in physics, has written two books on golf both having as central concept exactly the idea of the slow heavy hit. So posters should not feel ashamed a bit when having it all wrong.




Final opinion poll result:

P.S.: Animations were taken from 'The physics classroom tutorial'.[/center]

[jmessner]

mandrin,

Yes, indeed, there was an unexpected punch line for some of us (me included). I totally ignored the propagation issue as I was more focused on bending of the shaft (assumed zero in this case by definition) disturbing the more normal dynamics. I wasn't even thinking about the time domain. Arghh!

So, now, put the shaft perpendicular to the clubhead path like in a normal swing. I've been convinced that the flexibility of the shaft decouples it from the mass of the clubhead at impact(and therefore eliminates any "heavy hit"), but how does the propagation concept come in to play in this case? Edit for clarity: Is the decoupling due to the shaft flexibility in that clubhead path direction, or is it more due to the propogation delay? Maybe a combination?

Jay

[Biffer]

Hey, mandrin, this might be your best thread ever. Too bad nmgolfer isn't around to give us his take, which would undoubtedly be objective and enlightening. Also, I believe the engineer you speak of goes by the first name of Mindy, who I believe lived in Great Britain. Looking forward to see what you come up with next.....

[mandrin]

Originally Posted by Biffer

Hey, mandrin, this might be your best thread ever.

Biffer, thanks for the compliments. I appreciate

Originally Posted by Biffer

Too bad nmgolfer isn't around to give us his take, which would undoubtedly be objective and enlightening.

Why a vicious war when one can have peace. objective ???

Originally Posted by Biffer

Also, I believe the engineer you speak of goes by the first name of Mindy, who I believe lived in Great Britain. Looking forward to see what you come up with next.....

Indeed it is Mindy Blake. Made correction. Have no excuse having both books. Mindy Blake born in New Zealand. Obtained a masters degree and lectured in physics. Moved to England and joined the R.A.F. in 1936 and was a Squadron Commander in the Battle of Britain. Became a real war hero.

[Vicious Circle]

[savydan]

Awesome. One question in general:

You chose a 49 inch shaft.

If the shaft was 39 inches or shorter, then the propogation time would be less than 4 ten-thousands of a second.

So, on that basis, would the heavy mass come into play? Is it as simple as "all or nothing" depending on the length of the shaft?

In other words, if we cut that shaft inch by inch after each hit, would we reach a point where the heavy mass has a major effect?

[mandrin]

Originally Posted by jmessner

mandrin,

Yes, indeed, there was an unexpected punch line for some of us (me included). I totally ignored the propagation issue as I was more focused on bending of the shaft (assumed zero in this case by definition) disturbing the more normal dynamics. I wasn't even thinking about the time domain. Arghh!

So, now, put the shaft perpendicular to the clubhead path like in a normal swing. I've been convinced that the flexibility of the shaft decouples it from the mass of the clubhead at impact(and therefore eliminates any "heavy hit"), but how does the propagation concept come in to play in this case? Edit for clarity: Is the decoupling due to the shaft flexibility in that clubhead path direction, or is it more due to the propogation delay? Maybe a combination?

Jay

Jay,

In past posts I have used various types of arguments, each of them showing the fallacy of increasing the ‘effective mass’ of the club head or that of the ‘heavy hit‘. In the thread ‘Golf Impact Physics’ I did mention :

“that the analysis above is based on the traditional 'quasi-static' view of the shaft resisting impact. A true dynamic analysis however should consider the finite propagation time of the impact disturbance up and down the shaft. “

Indeed strictly looking from a standpoint of physics it is definitely the matter of propagation which is to be considered either for the shaft in line or making angle of 90 degrees. But it is easier to convince people with more down to earth arguments than using the more esoteric concept of propagation time.

I took deliberately the extreme inline case as it ‘allows’ to bring into play clearly ALL the weight of the ‘golfer’ behind the ball and yet even then it is completely in vain. Common sense indicates probably to everyone that putting the shaft at an angle of 90 degrees does not allow this anymore.

[jake2]

Originally Posted by mandrin

The impact disturbance propagates through the stainless shaft and is reflected back towards the ball.

In a thin stainless steel rod a disturbance propagates with a velocity of 5000 m/s.

The steel shaft length is 1.25 m, therefore the total propagation time, to and fro, is 0.0005 sec.

Impact duration is however less, i.e., 0.0004 sec.

Never would have thought of that. But it makes perfect sense now.

Thanks!

[mandrin]

Originally Posted by savydan

Awesome. One question in general:

You chose a 49 inch shaft.

If the shaft was 39 inches or shorter, then the propagation time would be less than 4 ten-thousands of a second.

So, on that basis, would the heavy mass come into play? Is it as simple as "all or nothing" depending on the length of the shaft?

In other words, if we cut that shaft inch by inch after each hit, would we reach a point where the heavy mass has a major effect?

savydan,

When you want to keep it simple there will invariably be someone asking some very pertinent question concerning the more difficult aspects of the problem. I will try however to give some plausible image how to view the behavior of the shaft as it behaves when impacted.

Look at the animation - a slender piece of material is approximated as consisting of small masses connected by springs. Imagine the heavy mass m1 and the clubhead mass m2 to be attached respectively at each end. Furthermore m3 is being impacted by the ensemble of m1, spring, and m2.

When impact occurs there will be a disturbance starting to travel through the spring. On a slower time scale the springs will start to compress longitudinally till eventually they form a compact solid mass and only then a full force can be transmitted along the shaft.

Hence you can see that for very small time intervals the shaft decouples both end but on a larger timescale it behaves as a truly solid mass being able to fully transmit a force applied at either end. In between we are dealing with complex dynamic transient effects quite difficult to analyze.

When I slowly sink into a swimming pool there is no resistance whatsoever. If I miss a dive however it starts hurting and water seems to less user friendly. If some one has the funny idea to dump me from a helicopter into a swimming pool the water behaves rather more like a solid. Hence the world around us depends strongly on the timescale used.

It is exactly for this reason that I used - ‘temporal dimension’ - as title for my post.

I might be tempted just for fun to analyze it further mathematically using the mechanical model as shown in the animation.

[jmessner]

Originally Posted by mandrin

Jay,

In past posts I have used various types of arguments, each of them showing the fallacy of increasing the ‘effective mass’ of the club head or that of the ‘heavy hit‘. In the thread ‘Golf Impact Physics’ I did mention :

“that the analysis above is based on the traditional 'quasi-static' view of the shaft resisting impact. A true dynamic analysis however should consider the finite propagation time of the impact disturbance up and down the shaft. “

Indeed strictly looking from a standpoint of physics it is definitely the matter of propagation which is to be considered either for the shaft in line or making angle of 90 degrees. But it is easier to convince people with more down to earth arguments than using the more esoteric concept of propagation time.

I took deliberately the extreme inline case as it ‘allows’ to bring into play clearly ALL the weight of the ‘golfer’ behind the ball and yet even then it is completely in vain. Common sense indicates probably to everyone that putting the shaft at an angle of 90 degrees does not allow this anymore.

mandrin,

You would think, but I wonder if some of folks on that other forum you mentioned at the start of this thread would say make the connection.

So, let's say the 90 degree shaft is inflexible. Using your analysis, the head might not be decoupled from the shaft completely, however, the head is certainly decoupled from any force exerted by the golfer (through PP#3 or whatever). Seems like a more compelling demonstration of this effect than I've seen previously. Cool!

Jay