Vacuum cleaner in a weightless environment

[Nantes]

Sorry for the vague title, I really wish the title character limit was longer.

Suppose you are floating in space without gravity, but instead of a vacuum, there is air all around you. You turn on a powerful vacuum cleaner with the nozzle pointed directly ahead of you. Ignore torque/rotational effects. To which direction are you propelled, and why?

This is easy to imagine with something like a leaf-blower: the device thrusts air forward, the air will react with an equal and opposite force, and the person using the blower will be thrust backwards. But I'm having a really hard time justifying that because a vacuum cleaner does the reverse (suck air in), the person would develop forward momentum. It just doesn't seem right.

Assuming that's what happens, I'm having a hard time because I can't picture at what part of the process the air molecules would be able to react with an opposite force in a way that would propel the astronaut forwards. In fact, as I imagine it, as the air molecules hit the back of the vacuum cleaner after being sucked in, they would exert a force to the backwards direction, thus propelling the astronaut that way.

Is it that both ejecting and sucking in air propel you backwards?

 

[jbriggs444]

Google "Feynman sprinkler".

 

[Nantes]

Interesting, thanks! I'm baffled that, seemingly, no one tried to replicate Feynman's experiment in more precise and less explosive conditions since then.

My problem is slightly different though, as I'm ignoring torque by pointing the sucking nozzle exactly directly in front of the astronaut's center of mass. Would he simply not move at all?

Has no astronaut experimented with this in the International Space Station?

 

[russ_watters]

Suppose you are floating in space without gravity, but instead of a vacuum, there is air all around you. You turn on a powerful vacuum cleaner with the nozzle pointed directly ahead of you. Ignore torque/rotational effects. To which direction are you propelled, and why?

This is easy to imagine with something like a leaf-blower: the device thrusts air forward, the air will react with an equal and opposite force, and the person using the blower will be thrust backwards. But I'm having a really hard time justifying that because a vacuum cleaner does the reverse (suck air in), the person would develop forward momentum. It just doesn't seem right.

In principle a vacuum cleaner and a leaf blower are the same thing and in reality some products are actually made to be both:
https://www.amazon.com/gp/product/B00FREQBXE/?tag=pfamazon01-20

https://www.shopvac.com/product/sho...-vacuum-with-detachable-blower-catnum:9314211

So consider that if air is going in one end it has to go out the other and re-assess...

 

[Nantes]

Oh, so there was the missing piece of the puzzle. I was ignoring that the air that was sucked in would have to come out somewhere! So the astronaut would be propelled to the opposite of the direction the outgoing air goes.

Thank you, kind sirs.

 

[Droidriven]

In principle a vacuum cleaner and a leaf blower are the same thing and in reality some products are actually made to be both:
https://www.amazon.com/gp/product/B00FREQBXE/?tag=pfamazon01-20

https://www.shopvac.com/product/sho...-vacuum-with-detachable-blower-catnum:9314211

So consider that if air is going in one end it has to go out the other and re-assess...

I was going to answer but your reply sums my reply.

 

[bland]

Google "Feynman sprinkler".

Ha, that was my first thought. When I first saw it it was obvious to me that the sprinkler would not move, and I was somewhat surprised to note that the great man had got it wrong!