F=ma and Bad Science

[saevel25]

I have to agree, but does it matter much for amateurs. There inconsistant swing will probably over shadow any marginal advantage to finding that one club that might be an outlier on the specs, than the others. I know pro's probably hit through dozen of the same drive to find an outlier that will give them 5-10 more yards.

[parallax]

The 'swing plane' is good example of 'junk science' in golf.

[iacas]

Originally Posted by parallax

The 'swing plane' is good example of 'junk science' in golf.

It depends on how you mean (and over how large of an area), but it can be, yes. It can still be a useful concept in many areas of the game.

[saevel25]

Can we just accept that its velocity we want to maximize, its not that difficult. Why do you think club makers want to maximize club head speed. There not going out there promoting acceleration. They know the physics, believe me they know more about ball flight laws than many instructors as well.

[parallax]

Originally Posted by iacas

It depends on how you mean (and over how large of an area), but it can be, yes. It can still be a useful concept in many areas of the game.

I agree that it can be useful, it is just that technically speaking a plane is a flat 2-dimensional surface. IMHO (i.e. I have no data to back this up), the 'sweet path arc' (I like this concept) only creates a 'plane' in the impact zone. The arc of the swing, from the top to the finish (as the concept 'swing plane' implies) creates a 3-d curved surface (not a plane).

Correct me if I am wrong...

As a swing model thought, I like it... it just doesn't match up with the scientific definition.

Kind of like acceleration... the only way to increase velocity is to accelerate. So the idea of accelerating through the ball is good if you want to maximize velocity.

[notsohard]

A 262 page thesis, "The effects of differing shaft dynamics on the biomechanics of a golf swing" by Nils Florian Betzler  (google it)

8.4 Conclusions
Overall, it was found that it is unlikely that changes in overall shaft stiffness in
themselves have a marked effect on driving performance.
Changes in shaft stiffness had no effect on the ball impact location on the club
face or face angle. There was no evidence to support the traditional notion that
dynamic loft and, consequently, launch angle would increase as shaft stiffness
decreased. In fact, one of the studies found lead strain at impact for the x-flex
shaft to be significantly higher than for the l-flex shaft, albeit by a small amount.
Nevertheless, marked differences in strain between shafts were detected for
other phases of the swing, in particular at the transition from backswing to
downswing.
Club head speed at impact was found to increase by a small amount (0.7 %)
but significantly for the group of golfers when shaft stiffness was reduced. This

was confirmed by the ball speed results, which indicated that ball speeds also
increased by 0.7 %. A number of factors were identified that contributed to the
increase in club head speed. First, club head speed was found to increase due
to the dynamic recovery process from lag to lead bending before impact, and
this effect was more pronounced for the l-flex shaft (0.8 % increase in club head
speed) than for the x-flex shaft (0.2 % increase). This was confirmed by the
strain measurements, which showed that the recovery rate from lag to lead was
significantly higher for the l-flex shaft. Second, the angular velocity of the grip of
the club was significantly higher for the l-flex shaft than for the x-flex shaft (0.5
%), potentially caused by an earlier wrist release that was detected for the x-flex
shaft. Current evidence from the robot study would tend to suggest that human
players did not adapt actively to changes in shaft stiffness, but further robot
testing is necessary to confirm this after removing oscillations in shaft bending.
Apart from changes in wrist angles at two downswing events, no change in
body kinematics was detected depending on the shaft conditions. This suggests
that either the players did not adapt their swing actively to shaft changes, or that
these adaptations were too small to be registered using an optical system.
Tests with a robot that supplied the same amount of „shoulder‟ torque for a
given arm angle regardless of shaft stiffness showed similar shaft effects on
wrist kinematics (later wrist release) and launch data (increase in ball speed) for
the l-flex club when the robot club head speed was set to approximately match
the mean club head speed achieved by the players. However, it is possible that
results obtained using the robot may not be directly comparable to the human
data due to differences in the shaft loading pattern.

[nick1998bunker]

Of course it involves golf! It's a law

[jamo]

Of course it involves golf! It's a law

Yes, but you have to know how to apply it correctly. Most people don't. You can't just pick a force, a mass, and an acceleration, and then cry out to Newton when what you gets is nonsensical.

[nick1998bunker]

Yes, but you have to know how to apply it correctly. Most people don't. You can't just pick a force, a mass, and an acceleration, and then cry out to Newton when what you gets is nonsensical.

Yes, I beleive it is the mass of the clubhead(slightly warped due to it being on a shaft and your holding it) and swingspeed.

[jamo]

Yes, I beleive it is the mass of the clubhead(slightly warped due to it being on a shaft and your holding it) and swingspeed.

It's F=ma. Where are you plugging in swing speed? That's the point I and other people made earlier in the thread (and other threads). There are better, easier, and more applicable equations to use.

[nick1998bunker]

It's F=ma. Where are you plugging in swing speed? That's the point I and other people made earlier in the thread (and other threads). There are better, easier, and more applicable equations to use.

yeah and too many other variables. Plus you will just get a number In newtons or something

[saevel25]

Not really, the beauty of all those brilliant people before our time is that they usually were pretty good at taking the physics down to something very applicable. Impact M1 x V1 = M2 x V2 Not that hard. throw in the coefficient of elasticity for the interaction and you got the golf ball impact. Guess what, we got that, its 0.830 for a driver. This is why Trackman works. Smash factor is just that equation above but modified. Ratio of Velocity = Smash Factor = (1 + COR) * Cos(SpinLoft) / (1 + Mass Ratio) You can see the components there. Velocity Ratio = V1 / V2 Mass Ratio = M1 / M2 Well, they might be inverted, but you get the idea. The rest of the stuff, its just to get you the reduction needed because its not a perfect inelastic collision. The clubface and ball both deform at impact. Physics is easy. Getting the derivation is tough. Its not rocket science though.

[krupa]

The F=ma argument is just a testament to how bad science gets propagated.  On a pool/billiard forum I got involved in an argument with a guy who tried to justify using E=mc² to talk about the power/energy of a break shot.

Next time you see a 'bad science' debate ask if there's gravity on the moon.  If they say 'no', ask how the astronauts walked around up there.  Chances are, they'll say "heavy boots".

[rehmwa]

Its not rocket science though.

well....actually, those kinds of equations pretty much are....

[saevel25]

Yea true, but much more complicated. Believe me, impacts, statics, that's easy stuff. Dynamics, Kinematics, thermodynamics, ect... That stuff is a pain in the ass. There's a reason why i left Mechanical Engineering for Civil Engineer ;)

[rehmwa]

I enjoyed our required Astrodynamics class in school.  But that was in the late '80's.  I'm sure that kids are doing that kind of work nowawadays in high school.

(Thermodynamics is what got my goat - it's just way too much accounting/tracking/balancing and looking stuff up in tables for me)

Thanks for doing the Civil Engineer thing.  I think courtesy is important in technical fields.

[boogielicious]

Yes, but you have to know how to apply it correctly. Most people don't.

You can't just pick a force, a mass, and an acceleration, and then cry out to Newton when what you gets is nonsensical.

Oh Jamo.  Wait until you start working with marketing folks or my favorite, the "a little knowledge is dangerous" workmate.  They come out of the woodwork at most companies.

[boogielicious]

I enjoyed our required Astrodynamics class in school.  But that was in the late '80's.  I'm sure that kids are doing that kind of work nowawadays in high school.

(Thermodynamics is what got my goat - it's just way too much accounting/tracking/balancing and looking stuff up in tables for me)

Thanks for doing the Civil Engineer thing.  I think courtesy is important in technical fields.

My grad school Chem E thermo was even more taxing.  The math was a complete different level than anything undergrad.