Hi, I hope I'm posting in the right forum. So I've been working on a game design and was toying with the idea of using acceleration and maximum speed. There are game design problems with not just putting a maximum speed on a ship like players never being able to catch each other. However I was thinking that there might be some interesting limits. One limit for example is the amount of acceleration a human body can withstand sustained. 3Gs is probably no problem but 10gs starts to get dangerous fast. My question is this. It was my understanding that space is not empty. Space is filled with molecules of matter, be it very hydrogen or space dust. My guess is the closer to planets and various other stellar objects the more junk there is. At what point does the speed of a space ship start building up dangerous friction when moving through these particles? Is it 1/10th of c, higher or lower? The second part of the question concerns thing about things like solar winds and the Casimir effect. Would these effect the metal hull of spaceship more as it increased in speed? Anything else you can think of? Any help would be appreciated.