I did not know where else to post this question but put it here since it is more related to mechanics than to astronomy. I am curious as to why small bits of space junk (bolts for example) are traveling so fast around Earth that they could poke holes in the International Space Station. Are different pieces of junk moving around Earth at different velocities even though they are located in similar (or the same) orbit? When I read news stories about space junk, the same number is mentioned as the speed of orbiting debris in space, approximately 17,000 mi/hr. Is it because although the objects are the same distance away from the surface of Earth, they might be traveling in different directions?