system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does everything that moves in outer space seem to move at extremely high velocities that could never be attained on Earth?

Or: Why does it seem that nothing moves slowly in outer space?
gpt
Firstly, it's a question of scale.  Space is huge compared to Earth.  What seems like an incredible speed here on Earth is actually very slow out in space, and it will take a long time to get anywhere.  For instance Neptune is travelling at 5 kilometers every second - a stupendously fast Earth speed - but it takes 168 years to go around the Sun.

Secondly, things on Earth don't move very fast for very long, because of air.  Travelling through atmosphere at space-speeds would be like slamming into a wall, simply because of how much air you need to move out of your way every second.  The fastest man-made objects are rockets, which gain most of their velocity way up high where the atmosphere is relatively thin.  They simply couldn't reach that speed at ground level.

Thirdly and perhaps most surprisingly, even if you could somehow overcome the atmosphere, you run into another problem.  If you're going fast enough (even on the ground), you'll reach escape velocity, and never come back down!  As you're tearing across the landscape at a few km/s, the Earth's surface curves away underneath you faster than gravity pulls you down, and you rise up into the sky and disappear.  So anything travelling at space-speeds on Earth would soon be flying away in space anyway.

It's not really that things in space always move very fast; it's that things here on Earth can only move very slowly.