see also: Offset Timing | Balance+Commitment | Uphill | Pole-push Gearing

These diagrams show how different angles of the pole and positions of the pole tip in the snow determine the "reactive" forces that either push the skier forward or lift the skier's body upward.  

The blue arrow shows the force of the skier's push on the pole, down and back against the snow. 

But Newton's Third Law from physics says that every force has an opposite reactive force -- and this "reactive" force can be analyzed according to two components: 

green arrow for the forward-push on the skier 

red arrow for the upward force on the skier 

The longer the arrow, the stronger magnitude of that force component. 

The action force on the pole is down and back, so the components of the "reactive" force are up and forward.  Forward is always good in classic stride, but upward can be good or bad -- good during the glide phase, bad during the kick phase. 

Physics says that the two components have to "add" together in the "geometry" of the diagram.  And you can see how the red and the green start from the "arrow target" of the blue arrow, and "bring it back" to the "arrow source" of the blue.  

(1) Skier leaning on pole for balance.  

No green arrow because there is no forward-push force.  All the reactive force is vertical upward on the skier's body -- so if the skier is trying to kick, it will counter-act the down-force needed for grip. 

(2) Initiation of pole-push with offset pole timing. 

Here there is some forward-push component.  The vertical up-force is larger -- but that's OK, because the skier has not yet begun the leg-push. 

But if this position is used to initiate the pole-push with timing synchronized with the leg-push, then it is not good -- since the large reactive up-force component hinders grip needed for the leg-push. 

(3) Initiation of pole-push with synchronized timing -- at the same time as the start of the kick. 

There is a large up-force component which counter-acts the down-force needed for best grip.

The best a skier can do with synchonized pole-push timing is to plant the pole-tip further back, to make the up-force component smaller. 

(4) Initiation of the kick with offset timing.  The pole-push hand has almost reached the leg, but no quite.  

There is some up-force which hinders kick, but not as much as with the start of the kick for synchronized timing. 

(5) Finish of the pole-push in classic stride. 

There is still some up-force, but the forward-push component is significantly larger. 

see also: Offset Timing | Balance+Commitment | Uphill | Pole-push Gearing

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