ive been trying to udnerstand for a while how contact forces interact with objects, a issue i can never sort out is weather a object will stop after applying force to another object or will move with it and continue to apply said force.

ill give you an example, when you put a object on a seesaw which was previously balanced that objects force is then applied to the seesaw becuase it made contact, this force will be equal to the original weight and the newtons 2nd law force applied back on the object will be equal ie normal force is also weight. my issue is that if there is an equal and opposite force applied on the object equal to its weight why would the object keep moving as its new force is 0?

this issue can then be expanded to all simmiler situations with objects and contact forces and you see why this is an issue for me. any insight into this would be greatly appriciated as i cant seem to get an answer out of anyone i ask. (pic related)