system
Given the following post, respond as if you're commenting on Reddit:
human
What starts the movement of an meteor or a comet? What force made it move initially?

What makes a random object such as a meteor to fly pass planets, what was the initial force or push that starts it's movement? Since Inertia might apply over here(unless it doesn't, the correct me if I'm wrong), wouldn't the space rocks stay in a place, unless an external force is applied on it.
gpt
Much of this motion begins during the gravitational collapse of a molecular cloud around a newly formed star.

As the protostar's gravity pulls the gas and dust into it, conservation of angular momentum will flatten that gas and dust into a rotating disk around the star (the protoplanetary disks you may have heard about).

The exact process of the formation of larger bodies (such as comets, asteroids, and planets) from this gas and dust is still a matter of some debate, but as they do form, they begin to be affected not only by the gravity and orbital motion from the star and the disk, but from each other as well.

So you can imagine a large planet or gas-giant forming and "sweeping" out a path of gas, dust, asteroids, and comets from the disk.  As that large planet barrels through these, their interactions can fling the comets out of the solar system and into the orbits that we see today, only coming back into the solar system to plunge toward the star on huge time scales.

But it all comes back to the motion imparted by the initial gravitational collapse of gas and dust around a new star.  Of course, you can trace it back further if you wish (how did the star collapse to start with?), but I'll leave it at this for now.