# Wooden Rope Bridge Animation

Hi Guys, I have a question, I have made a Rope bridge using Geo nodes, and I animated them using the simulation node, but, i want the bridge toreact to the objects walking over it, example a person or ball, can someone sujjest me how to fix that??
Will attaching an empty to an objet then to the bridge and controlling the movement works? or is there any easier way?? Please Help.

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Maybe I would try a proximity solution !? … The further the object gets to the middle of the bridge, the stronger the proximity effect gets to bend the bridge.

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What you have looks really good!

I haven’t tried to decipher your node-group,
but ropes, chains, cables, & rope-bridges should describe a Catenary curve when in equilibrium.

In non-equilibrium cases (for instance: subject to gusting wind that starts the bridge swinging sideways), the entire catenary curve could exhibit pendular motion, or if the wind (external forces) are not exactly perpendicular to the bridge, then you might get traveling waves (sloshing back and forth along the length of the bridge – not necessarily in sync between the 2 side guardrails.

If you are looking for a real physics simulation, be forewarned that Oscillation Modes can rapidly become pretty complex & strange, and multiple modes can exist at the same time, adding in harmonic fashion. This page: https://www.varmintal.com/amode.htm has a bunch of animated-GIFs demonstrating the various harmonic motions that a rifle-barrel can exhibit.

The physics gets worse and worse, the deeper you dig, and the closer you want your simulation to reflect reality.

So…
for animation purposes,
it’s probably better to aim for a “close-enough” effect.
When the bridge is hanging with no load (nothing walking across the bridge), it’s probably close enough to simulate a parabola, even though Physicists will flinch.

When you have some load moving across the bridge, the weight of the load matters.
Beyond “max-load”, the bridge will break, so let’s ignore that case.
At “max-load”, the bridge will deflect downward as far as possible at point of load, such that all slack (catenary / parabolic deflection) will turn into straight lines. Assuming you have non-elastic ropes (no stretching), the bridge will now describe 2 line segments:
L1 = distance between 2 end points of bridge
L2 = length of rope. L2 > L1
p = point of load (say, measured from Left end point of bridge) ( 0 <= p <= L1)
at point p, the bridge will have max deflection vertically from horizontal line.
D = max deflection

At less than Max-Load: the load will deflect downward less than Max-Deflection D … basically, the load is not enough to lift the legs A & B up to straight lines, so from some reduced D2 < D, you would need to model 2 separate Catenary/Parabola legs A2 & B2.

When you get this math built into your node-group, as a function of load-point ‘p’, it will be easy enough to move ‘p’ along the bridge as 1 person walks across.

I hope some of this helps, and that I haven’t made some egregious errors in the above math… it’s pretty late here.

Edit:
orange circled equation for A:
mistake spotted: change -2pL1 to +2pL1.

it’s late.

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Aww! Thank you so much for the invaluable information, I really appreciate it. Looks like your major is physics
Yes definitely,I will see what can i do for that. I liked this sentence never thought of it before:
“The physics gets worse and worse, the deeper you dig, and the closer you want your simulation to reflect reality.”

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Its ok, no worries at all. Amazing! Thanks

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