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Odd Question about Physics....
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Astrid Stjerna
Sebiestor Tribe
#1 - 2012-03-06 17:04:14 UTC
If the crew of a spacecraft put their weight against the wall and pushed, would they be able to 'shove' the spacecraft off-course? Basic physics (action/reaction) would suggest 'yes', but a spacecraft is way more massive than a typical human, which means 'not likely'.

Curious mind wants to know....

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Micheal Dietrich
Kings Gambit Black
#2 - 2012-03-06 17:29:10 UTC  |  Edited by: Micheal Dietrich
Can you push your car while sitting inside of it?

Kind of a shady example so here:

The shuttle has more mass than any of the astronauts, and while you are pushing on it, it is pushing back on you. The object with the lesser mass is inclined to move first.

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stoicfaux
#3 - 2012-03-06 17:55:27 UTC  |  Edited by: stoicfaux
Astrid Stjerna wrote:
If the crew of a spacecraft put their weight against the wall and pushed, would they be able to 'shove' the spacecraft off-course? Basic physics (action/reaction) would suggest 'yes', but a spacecraft is way more massive than a typical human, which means 'not likely'.

Yes. In fact, the crew does that whenever the spacecraft accelerates. Unless you're standing perfectly perpendicular to the force of the engines (or your mass is counter-balanced, etc.), your lump of mass will cause the ship's direction to deviate slightly.

However, the deviation should be so slight as to probably not be worth mentioning unless we're looking at a ship that for some reason doesn't have a working attitude control system over long periods of time.

edit:
To be clear, if the ship is drifting (not under thrust) then slamming yourself against the bulkhead won't do anything except maybe cause the ship to slightly spin. If slamming yourself against the bulkhead causes the paint or a piece of equipment to fly off then you're caused a slight course change. If you step outside with an MMU and ram the ship, you'll cause a course change. However, the mass of the ship will probably make such a course change imperceptible.

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Adunh Slavy
#4 - 2012-03-06 20:56:09 UTC
If they pushed? "Pushed"? ... I sense a trick question. What are they pushing from? What is their counter weight? Something else attached to the ship? ... Pushing in two directions at once? I'd be more concerned about a hull breach, then who cares if it is off course, cause they're all dead anyway.

We can take another idea, they all jump up and fling them selves at the ceiling. Well they had to push from the floor with X amount of energy, and then that same X amount of kinetic energy gets smacked against the opposite wall. So while they are floating happily across the room, the ship is off course, when they smack the opposite wall, the ship is back on course.

Probably easier to set the ship into rotation.

Right? WHo has a space ship so we can go test this.

Necessity is the plea for every infringement of human freedom. It is the argument of tyrants; it is the creed of slaves.  - William Pitt
Astrid Stjerna
Sebiestor Tribe
#5 - 2012-03-07 16:19:38 UTC
Adunh Slavy wrote:
If they pushed? "Pushed"? ... I sense a trick question. What are they pushing from? What is their counter weight? Something else attached to the ship? ... Pushing in two directions at once? I'd be more concerned about a hull breach, then who cares if it is off course, cause they're all dead anyway.

We can take another idea, they all jump up and fling them selves at the ceiling. Well they had to push from the floor with X amount of energy, and then that same X amount of kinetic energy gets smacked against the opposite wall. So while they are floating happily across the room, the ship is off course, when they smack the opposite wall, the ship is back on course.

Probably easier to set the ship into rotation.

Right? WHo has a space ship so we can go test this.



No trick question here, but your example has a flaw -- space is frictionless, so pushing the craft off-course means that it'll keep moving until an outside force (such as a guidance thruster) acts to stop it. Slamming against the opposite wall wall won't put the craft back on course, because by the time you hit that wall, the craft will have pitched around to a new angle and hitting the wall will only knock it out of that position.

Equal and opposite reaction -- if I push 'down' on your hand while in zero-g, I fly 'up' with energy proportionate to the force I applied.

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Micheal Dietrich
Kings Gambit Black
#6 - 2012-03-07 16:53:15 UTC
Astrid Stjerna wrote:
Adunh Slavy wrote:
If they pushed? "Pushed"? ... I sense a trick question. What are they pushing from? What is their counter weight? Something else attached to the ship? ... Pushing in two directions at once? I'd be more concerned about a hull breach, then who cares if it is off course, cause they're all dead anyway.

We can take another idea, they all jump up and fling them selves at the ceiling. Well they had to push from the floor with X amount of energy, and then that same X amount of kinetic energy gets smacked against the opposite wall. So while they are floating happily across the room, the ship is off course, when they smack the opposite wall, the ship is back on course.

Probably easier to set the ship into rotation.

Right? WHo has a space ship so we can go test this.



No trick question here, but your example has a flaw -- space is frictionless, so pushing the craft off-course means that it'll keep moving until an outside force (such as a guidance thruster) acts to stop it. Slamming against the opposite wall wall won't put the craft back on course, because by the time you hit that wall, the craft will have pitched around to a new angle and hitting the wall will only knock it out of that position.

Equal and opposite reaction -- if I push 'down' on your hand while in zero-g, I fly 'up' with energy proportionate to the force I applied.



Again, the mass of the shuttle is far larger than the mass of the person so the greater force will be exerted on the person. Mf <---->Fm. There may be no resistance in space but this doesn't make your average astronaut Superman. There is no way they can create enough inertia to move the shuttle by any noticeable means. Hence why we don't see the ISS doing somersaults in space right now.

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Astrid Stjerna
Sebiestor Tribe
#7 - 2012-03-07 16:58:41 UTC
Micheal Dietrich wrote:

Again, the mass of the shuttle is far larger than the mass of the person so the greater force will be exerted on the person. Mf <---->Fm. There may be no resistance in space but this doesn't make your average astronaut Superman. There is no way they can create enough inertia to move the shuttle by any noticeable means. Hence why we don't see the ISS doing somersaults in space right now.


Yeah, I know -- Iw as just correcting the assumption that you can knock a ship back 'on course' in the manner the other fellow described.

Really, I was just curious. I know that it can't actually happen in any reasonable way, but I was still interested to see if the laws of physics would allow it in an 'ideal' situation.

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Adunh Slavy
#8 - 2012-03-07 19:25:29 UTC
Astrid Stjerna wrote:

No trick question here, but your example has a flaw -- space is frictionless, so pushing the craft off-course means that it'll keep moving until an outside force (such as a guidance thruster) acts to stop it. Slamming against the opposite wall wall won't put the craft back on course, because by the time you hit that wall, the craft will have pitched around to a new angle and hitting the wall will only knock it out of that position.

Equal and opposite reaction -- if I push 'down' on your hand while in zero-g, I fly 'up' with energy proportionate to the force I applied.



This is why I mentioned it would be easier to put the ship into rotation, and that is only true if the angle of "push" and "impact" is not going through the center of mass, right? Also, your original example never stated the ship was in a powered mode or not.

Since space is indeed frictionless, a ship under power all the time is rather wasteful of fuel. Also, if the people in the ship have time to play and jump around, they are probably not under power and accelerating, strapped into their space cadet chairs, or else they'd be squished back into little space toilet in the back room. So you'll excuse me for making an assumption in the details you left out. :)

Now if the ship were under power and they could indeed alter the pitch or yaw by push/impact, and not going through the center of mass, then yes, altering the pitch or yaw, altering the rotation, could send the ship off course. If the ship is not under power and traveling by inertia, then if they do manage to set the ship into rotation, it will simply rotate as it continues along its course.

Necessity is the plea for every infringement of human freedom. It is the argument of tyrants; it is the creed of slaves.  - William Pitt