[Tom Bishop]

I found an interesting video by a man who claims that rockets should not work in space.

[Tom Bishop]

I think this could be a subject worth further investigation. I would like to see one more experiment tried, with a barrier that is not attached to the vehicle. For instance, what would happen if he put his outstretched palm following the exhaust pipe at a distance of two inches as the car sped away? Would the car speed up since his hand is more solid than the atmosphere? I think that might be more conclusive evidence.

Are there any other ways which can prove or disprove his theory which seems to suggest that Newton's Third Law is false?

[Hoppy]

Tom, there was discussion on the other site about this subject. A rocket is actually pushing on the atmosphere to move. I don't think it would work in space. How is rocket exhaust making an equal and opposite reaction with the rocket nozzle while still inside the nozzle. That would be similar to you pushing yourself off of a chair, by pushing your arm against your leg. It is not going to move you.

[garygreen]

Instead of beating around the bush, why not make/buy a vacuum chamber and test your hypothesis yourself?

[Tom Bishop]

Instead of beating around the bush, why not make/buy a vacuum chamber and test your hypothesis yourself?

Hoppy is correct, the equal and opposite reaction theory given for rockets does not make sense.

I did find some instructions for making a vaccum chamber: http://www.instructables.com/id/Pressure-Cooker-Vacuum-Chamber/

Perhaps this can be an activity the society can fundraise for.

[Rayzor]

Rockets work just fine in space,  it's just simply conservation of momentum.   

http://www.discovery.com/tv-shows/mythbusters/videos/its-rocket-science/

[Jura-Glenlivet]

The misconception that the rocket is pushing against the air behind it is common, but this would be partially cancelled out by the air ahead of the rocket resisting the movement.

The rocket is expelling explosively, particles (burnt fuel) it is pushing against this ejected gas, and this works just as well in space.

[LuggerSailor]

Sit on a swing with a bowling ball and a larger beach ball in your lap.
Have a friend watching to observe your displacement while you do the following;
   1. Throw the beach ball away as hard as you can.
   2. Throw the bowling ball away as hard as you can.

You and the swing are expelling mass (the balls). One is heavy, the other is light. One displaces more atmosphere than the other.

I'm not even going to suggest the expected results of this experiment, I'll leave it to the Zetetics.

[markjo]

Hoppy is correct, the equal and opposite reaction theory given for rockets does not make sense.

Actually, it does if you understand where the action/reaction pairings are occurring (primarily within the combustion chamber).

[Tom Bishop]

Rockets work just fine in space,  it's just simply conservation of momentum.   

http://www.discovery.com/tv-shows/mythbusters/videos/its-rocket-science/

Thank you for that link. I agree that it appears that the rocket did work in a vacuum. However, on reassessment of the idea, I do not think a relatively small vaccum chamber would be an appropriate test of this theory.

The author of the video would assert that rather that, rather than the atmosphere, the bottle rocket is pushing off of the pixiglass door behind the rocket in this experiment, and his theory holds.

[garygreen]

Instead of beating around the bush, why not make/buy a vacuum chamber and test your hypothesis yourself?

Perhaps this can be an activity the society can fundraise for.

That's obviously never, ever going to happen.

Instead of making pie-in-the-sky plans that will never come to fruition, why not just spend the money to test your hypothesis on your own?  We're only talking about a few hundred bucks here; maybe a grand if you wanted to build something pretty nice.  Maybe front the money for the equipment, conduct the experiment, make a detailed recording of your expenses, and then try to raise funds to cover those costs.  I would genuinely be happy to throw a few bucks your way to offset the cost of such an experiment so long as it was well-documented.  I imagine others would as well.

My point is that you probably already have the means to test your hypothesis and record your results here.  Why merely take the word of a YouTube video?

[Tom Bishop]

Instead of beating around the bush, why not make/buy a vacuum chamber and test your hypothesis yourself?

Perhaps this can be an activity the society can fundraise for.

That's obviously never, ever going to happen.

Instead of making pie-in-the-sky plans that will never come to fruition, why not just spend the money to test your hypothesis on your own?  We're only talking about a few hundred bucks here; maybe a grand if you wanted to build something pretty nice.  Maybe front the money for the equipment, conduct the experiment, make a detailed recording of your expenses, and then try to raise funds to cover those costs.  I would genuinely be happy to throw a few bucks your way to offset the cost of such an experiment so long as it was well-documented.  I imagine others would as well.

My point is that you probably already have the means to test your hypothesis and record your results here.  Why merely take the word of a YouTube video?

Upon some reflection on the theory as stated in the video, I no longer believe that a small vacuum chamber can test this effect. It can be argued by proponents of the theory that the craft is pushing off of a wall of the chamber, rather than the atmosphere, and that nothing would be demonstrated either way.

I revert back to my original experiment, and think if the balloon car from the first experiment sped up when there was a solid body put near its exhaust area, it would demonstrate the theory to be true.

I would like to see one more experiment tried, with a barrier that is not attached to the vehicle. For instance, what would happen if he put his outstretched palm following the exhaust pipe at a distance of two inches as the car sped away? Would the car speed up since his hand is more solid than the atmosphere? I think that might be more conclusive evidence.

Do you have any comments on the validity of such an experiment?

[markjo]

I would like to see one more experiment tried, with a barrier that is not attached to the vehicle. For instance, what would happen if he put his outstretched palm following the exhaust pipe at a distance of two inches as the car sped away? Would the car speed up since his hand is more solid than the atmosphere? I think that might be more conclusive evidence.

Do you have any comments on the validity of such an experiment?

Since air is essentially invisible to the naked eye, it can pretty hard to follow exactly what's going on.  I would suggest filling the balloon with smoke and recording the various tests (hand right next to exhaust, 1 inch away, 2 inches, etc.) in slow motion (many new camera phones have this ability).  My guess is that there would be a certain amount of exhaust "bouncing" off the hand and interacting with the car for a second time.  However, I suspect that this "pogo" effect would drop off quickly as you move your hand further away.  Still, it might be interesting to test.

*Edit*
One thing to keep in mind is that even if a rocket's exhaust does bounce off the ground and push back against the bottom of a rocket, that is generally considered a bad thing.  That's why there are usually large pits under the launch pads to deflect the exhaust away from the rocket.

[Hoppy]

Rockets work just fine in space,  it's just simply conservation of momentum.   

http://www.discovery.com/tv-shows/mythbusters/videos/its-rocket-science/

Thank you for that link. I agree that it appears that the rocket did work in a vacuum. However, on reassessment of the idea, I do not think a relatively small vaccum chamber would be an appropriate test of this theory.

The author of the video would assert that rather that, rather than the atmosphere, the bottle rocket is pushing off of the pixiglass door behind the rocket in this experiment, and his theory holds.

That box is not a true vacuum, I saw a vid on the other site where near vacuum pressure inplodes a steel railroad tanker car. It just folded up like an accordian. There is no way that plexi box was a vacuum.

[markjo]

That box is not a true vacuum, I saw a vid on the other site where near vacuum pressure inplodes a steel railroad tanker car. It just folded up like an accordian. There is no way that plexi box was a vacuum.

Railroad tanker cars are designed to resist the forces of their contents pressing outwards, not necessarily forces from the outside pressing inwards.

[Hoppy]

That box is not a true vacuum, I saw a vid on the other site where near vacuum pressure inplodes a steel railroad tanker car. It just folded up like an accordian. There is no way that plexi box was a vacuum.

Railroad tanker cars are designed to resist the forces of their contents pressing outwards, not necessarily forces from the outside pressing inwards.

Irrelevant. What is a home made plexiglass box designed for?

[markjo]

That box is not a true vacuum, I saw a vid on the other site where near vacuum pressure inplodes a steel railroad tanker car. It just folded up like an accordian. There is no way that plexi box was a vacuum.

Railroad tanker cars are designed to resist the forces of their contents pressing outwards, not necessarily forces from the outside pressing inwards.

Irrelevant.

Then why did you bring it up?

What is a home made plexiglass box designed for?

That would depend on who designed it and why.

[Tom Bishop]

It doesn't really matter. Even if it were a vacuum, under the theory provided by the author of the video in the OP, where the entire system acts as one, the rocket is just pushing off of the solid Plexiglas door rather than the atmosphere. There is no demonstration that the propelling mechanism is due to the ejection of matter from the engine as stated by rocket scientists.

[garygreen]

Upon some reflection on the theory as stated in the video, I no longer believe that a small vacuum chamber can test this effect. It can be argued by proponents of the theory that the craft is pushing off of a wall of the chamber, rather than the atmosphere, and that nothing would be demonstrated either way.

I think this explanation still requires Newton's Third Law as a premise; it merely moves the discussion of action-reaction pairs from rockets and exhaust particles, to exhaust particles and walls.  If we're talking about exhaust "pushing" the rocket off of a wall, then we're still talking about Newton's Third.  The rocket pushes on the wall, and the wall pushes back.  But if Newton's Third Law is correct, then thrust is perfectly understandable via the action-reaction pair of exhaust particles and the rocket that accelerated them.  Exhaust particles cannot be accelerated out of the nozzle without the application of a force, and the application of that force must correspond to a force of equal magnitude in the opposite direction.

It's also not clear to me, contrary to Newton's explanation of thrust, how the process of pushing off the wall in this manner works.  A particle leaves the nozzle and collides with a wall.  Then what?  How does the particle of exhaust hitting a wall accelerate the vehicle it just left behind?

I would like to see one more experiment tried, with a barrier that is not attached to the vehicle. For instance, what would happen if he put his outstretched palm following the exhaust pipe at a distance of two inches as the car sped away? Would the car speed up since his hand is more solid than the atmosphere? I think that might be more conclusive evidence.

Do you have any comments on the validity of such an experiment?

I definitely think that this a better experiment than the one in the video.  I think the guy in the video did the equivalent of attaching parachutes directly behind a jet engine and then arguing that it proves jet engines don't work: the force of the air on the paper is opposite the direction of thrust.

I'm no physicist, but it sounds like a good experiment to me if you control it rigorously.  The conditions of each trial should be identical except for the placement of the barrier.   

[Tom Bishop]

I think this explanation still requires Newton's Third Law as a premise; it merely moves the discussion of action-reaction pairs from rockets and exhaust particles, to exhaust particles and walls.  If we're talking about exhaust "pushing" the rocket off of a wall, then we're still talking about Newton's Third.  The rocket pushes on the wall, and the wall pushes back.  But if Newton's Third Law is correct, then thrust is perfectly understandable via the action-reaction pair of exhaust particles and the rocket that accelerated them.  Exhaust particles cannot be accelerated out of the nozzle without the application of a force, and the application of that force must correspond to a force of equal magnitude in the opposite direction.

Why must the exhaust of particles correspond to a force of equal magnitude in empty space? That does not make any sense.

What makes sense is if the particles are hitting something, pushing the entire vehicle system, exhaust and all, forward.

It's also not clear to me, contrary to Newton's explanation of thrust, how the process of pushing off the wall in this manner works.  A particle leaves the nozzle and collides with a wall.  Then what?  How does the particle of exhaust hitting a wall accelerate the vehicle it just left behind?

The exhaust is a high pressure fluid. It is connected to the vehicle. As the exhaust encounters resistance, that resistance will trickle back to the vehicle.

It's like one of those water jetpacks. The jetpack does not rise in altitude until the water has hit the surface. The high pressured water is connected to the jetpack as a single entity. Resistance on the water results resistance on the jetpack. The tension ripples upwards through the whole entity.