eli5: If space is a vacuum, how can rockets work? What are the thrusters pushing *against* if there is nothing out there?

Question

I’ve never really understood the physics of this. Obviously it works somehow — I’m not a moonlanding denier or anything — but my (admittedly primitive) brain continues to insist that a rocket thruster needs something to push *against* in order to work.

So what is it pushing against if space is essentially a void?

In: 7157

Answer 1

Rockets don’t work by pushing against something. They work by throwing something out in one direction really fast (rocket exhaust) and the reaction is that they move in the opposition direction.

Physically, it’s the same as if you were sitting in a rolling chair and threw a heavy bowling ball or something, it’ll push you back. The rocket is just throwing lots of little bowling balls (particles) really really really fast (and in physics fast particles = hot).