i don't know if this question is ok in the bike mechanics section but here is the question

i was riding on a wooden bridge with planks perpendicular to my direction and i noticed that my fork was going moving up and down a lot about an inch. is that ok? i am thinking that the fork does that for shock absorbance but that much? thanks.

Your question is too vague. What kind of fork? Road, MTB? Rigid, suspension? Steel, aluminum, carbon? Fork moving up & down or laterally front to back?

If it's a suspension fork, it's designed to do that. Mine moves 6" up.

hehehehe i didn't specify. its a fork from a trek 520. other words a road fork. you know how the fork is arched well it just bends more

That's not good at all. Replace the fork. The fork was not built to handle that kind of stress.

Are you sure it was flex and not the wheel just bouncing? Steel flexes, but not an inch without giving up a significant amount of lateral stability.

My Reynolds 531 ST steel forks have plenty of flex over rough surfaces, and I can often see 1cm of movement in the hub when I go over a really rough road.
Steel road forks are pretty springy and designed to flex. Steel MTB forks are much more ridgid.