Pun intended, but still a serious question.
Would a neutron matter? (Pun also intended, but also serious)
This is why Star Trek’s Enterprise has that forward-facing deflector dish. It wouldn’t last very long without something to prevent such collisions.
It’s actually a legit concern with any (hypothetical) interstellar mission. Even hydrogen atoms will hit with significant force. Dust hits like nukes, and an asteroid is just game over.
The maxim used in a lot of sci-fi is an ablative armour plate. Often in the form of ice. Interstellar ships would likely aldo be needle like, to minimise their cross section. We could also use electric and/or magnetic fields to move smaller particles out of the way.
As for densities, I believe it’s a couple of hydrogen ions per m^3 . Dust is rarer, but still present. It’s only bigger rocks that are rare enough to just hope to avoid.
Didn’t one of the space shuttles almost holed by a fleck of paint?
Challenger had a fleck of paint damage one of its windows on an early mission.
The ISS has been pinholed by debris a few times. Likely paint. The shuttle was damaged by foam breaking off, amongst other events.
By comparison orbital velocity is around 7km/s, while a bullet is around 0.367km/s. Any mismatch will push debris up to bullet speeds easily.
As for relativistic speeds. C is 300,000km/s assuming you get up to 1/3C (barely relativistic) you are moving at 100,000km/s or 14,000x faster than the ISS moves, or 39000x faster than a bullet. A 10g rock would hit with 10kilotons of energy. About 2/3 the energy of the first atom. bombs.
PBS SpaceTime has a great video about this topic (see @ ~7min to get your specific question)
Link with timestamp for the lazy: https://youtu.be/wdP_UDSsuro?t=420
Yes. For the effects, look up pictures of the damage that space debris has on spacecrafts.
Mind to post your favourite example?
The fastest human made object moves at 1/1000 of the speed of light
Depends on the strength of your navigational deflector.
