This might be a stupid question, but I am trying to understand the fundamentals.

The closest I've come to is Newton's Third law of Motion which states for every action (force) in nature there is an equal and opposite reaction. So if we are expending energy by firing rockets in one direction there must be a reaction that push us forward. This seems easy to understand on earth (ie. pushing back the ground or atmosphere) but in vacuum of space what are we pushing backwards.

I don't want to accept, with all due respect, Just because Newton said so.

While this seems so obvious that this is the expected behaviour but is there some underlying physics that can help me understand this better?

One surprising theory might be dark matter but that rises many more questions like does it still qualify as vacuum if there is dark matter and also an obvious one, have we ever calculated that?

Edit: ground pushing us forward might seem a bit abstract so here is what I remember from my high school physics, If Object A pushes Object B, then Object B pushes Object A at exactly the same time, with exactly the same amount of force, but in the opposite direction. The reason the Earth pushes up on you with the same force has to do with the nature of solids. When you stand on the ground, you are actually compressing the dirt beneath you. This compression also applies to the billions of interparticle and intermolecular electrochemical bonds in the solid matter of the Earth, which act a bit like little springs holding things together down at the atomic level.
Cars, boats, airplanes, and humans move forwards by pushing back on the ground, the water, or the air. Above text is copied from here -> Blog post on Third law of Motion

ps. Not related, but will the airplanes stop working is we take away the atmosphere from Earth.

  • $\begingroup$ hey can you please elaborate $\endgroup$ – Anonymous Nov 25 '20 at 11:18
  • $\begingroup$ how pushing forward $\endgroup$ – Anonymous Nov 25 '20 at 11:19
  • $\begingroup$ sure, I'll update the question, hold on $\endgroup$ – Rishiraj Purohit Nov 25 '20 at 11:23
  • $\begingroup$ no problem, i have answered it without updation $\endgroup$ – Anonymous Nov 25 '20 at 11:28
  • $\begingroup$ it was pretty tough to understand but was understandable $\endgroup$ – Anonymous Nov 25 '20 at 11:28

but in vacuum of space what are we pushing backwards.

Actually when we launch a rocket the gases that eject from the rocket are responsible for providing the rocket a thrust(a push) and the gases strike te surface and thus loose there kinetic energy to earth surface(but is unobservable as you are in the frame of earth :) ). So when you say that you are launching a rocket from rocket launcher that provides you a backward force(you might not experience it completely but with a gun you can) momentum is conserved.

For macroscopic non relativistic bodies newton's laws are valid in every aspect and cannot be defied.

So in a nutshell in vaccum the gases will be ejected to obey conservation laws. enter image description here

GIF source google

  • $\begingroup$ So do those gases or molecules in them exert force on the rocket(lets say spaceship)? $\endgroup$ – Rishiraj Purohit Nov 25 '20 at 11:38
  • $\begingroup$ @RishirajPurohit yes(conservation of momentum) $\endgroup$ – Anonymous Nov 25 '20 at 13:23
  • $\begingroup$ @RishirajPurohit did you get your answer? $\endgroup$ – Anonymous Nov 25 '20 at 14:51

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