02c Exploiting GRF to be immovable

Ground reaction forces will oppose to infinity (or the practical limit of what your structure can handle) any incoming forces in a limited set of directions

immovable body

These directions are defined by the point of contact down to the base of support. If the directions drop lower than these angles then the mass of the person can assist.
To see this more clearly the mass of the person needs to be seen in relation to the GRF vector and the applied external forces. While it is usual to resolve forces in a vertical and horizontal line, in this case it is simplified to align them along the axis of the GRF
ground path forces

Here the applied force is represented by 2 lines and the mass is represented by two lines. One travels along the GRF line the other are in opposite directions. So long as the mass force is the largest you don't move.


So whats the take home messages here
- appropriately directioned forces can be repulsed by GRF
- you need a good structure (some call it the suit) to make this work
- if the direction of the applied force is outside of the range of limits of the GRF you might be able to redirect it
- using your bodies mass and by changng the geometry of the lever in the force diagrammes you can be stronger by 
a. move your mass closer to the applied force
b. bring the contact point fo the applied force closer to your mass
c. try to make the direction of the applied force be as vertically down as possible (to use GRF ) or vertically up (to make them have to lift you)