No_Mind Golf Science
where golf myths get debunked
"It's not what you don't know that hurts you, it's what you know that just ain't so." -- Mark Twain
There are those who believe momentum gets transfered from feet
up the golfer's "kinetic chain" finally reaching the clubhead.
These are the stuff of modern golf myths
Let us begin by considering what a "kinetic chain" is. Etymology tells us "kinetic" is from the Greek: kinetikos meaning "moving, putting in motion," from kinetos "moved," verbal adj. of kinein "to move." In mechanics (a branch of Newtonion physics) "kinetic" also pertains to forces or moments. Chain in this case implies mechanical linkage of separate parts or "links" of said chain. Therefore a kinetic chain allows for the transfer of forces and moments between links to create motion. The human muscular skeletal system is a kinetic chain. Bones are the links which meet at the joints and are moved via force (leverage) generated by muscle contractions applied to tendons spanning the joints. There many are other sorts of kinetic chains as well.
Consider a kinetic chain consiting of two masses that are joined by a cord (i.e. a flexible link) running throught their respective centers as shown in the figure above. One end of the cord is fixed and there is some slack between the hard point and the first mass and between the first and second mass'.
At time=0 we drop the two masses and they acquire momentum. At time=1 the first mass reaches the end of its leash and is brought to an abrupt stop. The second mass continues to fall.
How much momentum did the first mass transfer to the second mass when it was brought to halt? If you said none, congratulations that is correct. One part of the chain stopped and another part of the chain not only received no momentum from the first, it did not even know the first mass stopped!
At time=2 the second mass reaches the end of its leash and it too is brought to an abrubt stop.
How much momentum did the second mass transfer to the first mass? If you said none then then give yourself a gold star because that is correct. The first mass is already constrained from moving and therefor its momentum remains zero. Slowing/stopping of parts of a kinetic chain does not necessarily result in a transfer of momentum.
Momentum transfer is not AUTOMATIC or GUARANTEED between links in a chain!
Now lets consider the same kinetic chain only this time lets stretch it out as shown in the figure above. This kinetic chain is a double pendulum ( http://scienceworld.wolfram.com/physics/DoublePendulum.html ) and this time, it is different. As the first mass begins reaching the bottom of the swing, its does "transfer" some of its momentum the the second mass. So by tweeking the geometery (the kinematics) of our chain we are able to make a momentum transfer possible.
Momentum transfer in a kinetic chain depends on the kinematics!
What about our golfer you ask? We can't tweek our kinetic chain to enhance momentum transfer. Humans are stuck with the kinematics and kinetics God gave us and that's OK. Our kinetic chain consists of joints at the knees, hips and shoulders and elbows. These are connected by rigid links between: hands and elbow, elbow and shoulder, feet and knees, kees and hips. We have a FLEXIBLE link between the hips and shoulder girdle called a spine. The shoulder girdle is also quite flexible. .
Consider the belly dancer...Because the spine is flexible, momentum from the legs hips and abdomen are not tranfered to the shoulder girdle. We see massive motion in her lower body yet her shoulders are essentially quiescent.
Momentum is not normally transfered via flexible elements such as the spine and shoulder girdles. A golfers shoulders don't know his hips have stopped and left arm doesn't know the hips, or torso have stopped. These body parts are isolated by flexible links. What does that leave us with? It leaves the straight left arm. Indeed it is possible for some of the arm's momentum to transfer to the club via the wrist joint as is shown in the double pendulum kinetic chain example above. But that's it!
Everything the golfer does is aimed at making the left arm (and in turn the hands) move on the optimal kinematic path!
What have we learned? Lets review...
Momentum transfer in a kinetic chain depends on kinematics
Momentum transfer in kinetic chain depends on the nature of the links joining elements of the chain.
Humans are stuck with the kinematics (structure) and kinetics (muscles) God gave them
Golfers can tranfer momentum from their left arm to club but momentum contributions from other body mass' is dubious.