Please note that “Free” is referring to the notion of the vaulter experiencing minimal resistance from the pole that counters the vaulter’s motion (as represented by magnitude and direction of the vaulter’s total body centre of mass).
At no point anywhere in the vaulting process can the vaulter ever be truly “free” of the effect of the gravitational attractive force due to the distance apart of a vaulter and earth mass centres!
In running, jumping and projecting the body by means of a flexible pole, the vaulter is working against “gravity” (air resistance can be of assistance or a hindrance to vaulter motion depending on the environmental conditions) through direct and indirect contact with the surface of the earth. Upon the vaulter’s centre of mass reaching the peak height of its flight trajectory following pole release, the vaulter undergoes a vertically downward displacement accelerated by the negative downward direction vector and magnitude of the force of gravity.
I think understanding from a physics and biomechanical perspective the “how, what, where, when and why the composite material pole used in modern pole vault (post 1960 to date) is made to bend is the crux of problem and has yet to be understood by many coaches and many, if not most, relatively successful vaulters.
In your excellent, very clear exposition on the advantage to the vaulter of using a free take –off you do make an error in accepting that the planting box does not move upon the instant the pole tip makes contact with the rear wall!
Tim McMichael wrote:This goes to the fact that willreiffer is right about. From a purely physics standpoint, is is impossible for energy to go into the box. For that to happen the box would have to move.
The box does move!
Because the box is rigidly attached to the earth and the earth has an infinitesimally large mass relative to that of the vaulter the box is observed not to move whilst the vaulter possessing such a tiny relative mass experiences large effects, from the impact of the pole striking the earth, that are readily perceivable by both vaulter and external observer.
Newton’s action-reaction principle operates such that to every action there must be a simultaneous reaction of equal magnitude and opposed in direction. (If the box did not move Newtonian Law of Motion would not be operating! (It is accepted the collision in the impact is “elastic” not “plastic!”).
The inertial effect of the pole impacting the rear wall upon the vaulter, who is from that instant in contact with the earth via the pole, produces clearly observable changes to the motion of the vaulter’s centre of mass and has associated observable effects upon the vaulter’s body segment arrangement in relation to the hands gripping the pole. Some energy will be lost in the impact due to sound, friction and the “compliance” in the musculoskeletal system of the vaulter. On this I think there is agreement in viewpoints so far expressed.
Tim McMichael wrote:Any method that allows a vaulter to finish the vault and still land in the box is unsound. Not just because it us unsafe, though that is the main reason, but also because it will be a lower vault, even if it is successful.
Yes!!!!!!!!!!!!!!!!!!!! Yes!!!!!!!!!!!!!!!!!! I totally agree with you!!!
Tim McMichael wrote:That said, I do appreciate willreiffer's ideas and comments on this board. His was the majority point of view not too long ago and was advocated by no less that Dick Ganslen who was also coming from a physics background. It's good to rehash this debate, I think. If only because the arguments for an under takeoff can be surprisingly compelling.
Dick Ganslen, arguably the foremost Mechanics of the Pole Vault Guru of the late 50’s through to late 1970’s, did not, in my view, adequately consider the significance of the nature of the pole – planting box interaction dynamics in determining how, where, when and what occurs under differing combinations of pole-box impact phenomena.
Ganslen did introduce Euler beam bending theory considerations in pole performance but necessarily (given the era!) was limited to a purely statics analytical approach. Also, in my opinion, the publications gave disproportionate weight to the anecdotal evidence provided by the best vaulters of the day! In one sense this was admirable in that Ganslen did not censor the opinions being expressed even though he may possibly have had personal reservations as to the veracity of some of those opinions!
Forty years on the myths as to the efficiency and effectiveness of putting lots of stored elastic potential energy by pre-bending the pole before take-off are alive and well.
I hope that Willreifer and others will be persuaded that any advantage mechanically that may be obtained by this take-off technique of storing potential energy in the pole is “too costly” to the successful completion of the rest of the vault because of the high risk of catastrophic failure it presents for even the most successful vaulters on the planet let alone naive neophytes! (see video referenced below).
For those of us who have observed the evolution of Renaud Lavillenie’s technical development, let’s say from 2005 until his 6.16m World Indoor Pole Vault Record in 2014, it is clear that as his capacity to use longer grip lengths on longer and stiffer poles improved, his take-off point on the runway has moved from being “excessively” under in the horizontal direction toward that which minimizes pole resistance, namely a “Free Take-Off”. The laws of physics and mathematics dictate that this must be so given the constancies of the pole lengths and the vaulter anthropometry (stature, mass, body segment distribution of mass and segmental lengths, muscle mass cross sectional areas etc.,) on any specific vault attempt.
The formidable task necessitated by “ideal” take-off locations along the runway, even when very flexible poles are used relative to vaulter body mass, means that the vaulter has to achieve a greater amplitude of pole cord angle of rotation to be successful. This requirement in turn increases the vital necessity to safely rotate the total pole plus vaulter system towards the plane of the cross bar. The vaulter not only has to increase intentional focus on system rotation rather than pole bending but also must train to achieve greater proficiency and efficiency in optimizing the redirection of the transfer of momentum from the preceding run up and plant.
Given the relative ease and safety with which the Petrov-Bubka Approach can be and is being taught effectively to some beginners, it is interesting to speculate on what Renaud Lavillenie’s ultimate potential would / could be if he did not have to contend with the legacy of having learned to vault by taking off under and massively pre-bending the pole!
In the two jumps in this video below, one a Fantastic World Record and the next a World Record failed attempt could not better illustrate, to an unbiased viewer, the notion that simply using a massive pre-bend take-off is ineffectual, inefficient and inherently puts the vaulter at increased risk of injury.
It is my opinion a coach operating on this foundational misconception risks inculcating behavioural actions, beliefs and attitudes about pole vault technique that increases the intensity and probability of adverse pole vaulting outcomes for beginners and advanced pole vaulters alike that become extremely difficult to alter! This is despite the facts and wisdom known about the matter. C'est la vie!