Welcome to
Science a GoGo's
Discussion Forums
Please keep your postings on-topic or they will be moved to a galaxy far, far away.
Your use of this forum indicates your agreement to our terms of use.
So that we remain spam-free, please note that all posts by new users are moderated.


The Forums
General Science Talk        Not-Quite-Science        Climate Change Discussion        Physics Forum        Science Fiction

Who's Online
0 registered (), 294 Guests and 3 Spiders online.
Key: Admin, Global Mod, Mod
Latest Posts
Is there anybody out there?
by paul
Yesterday at 03:58 AM
Top Posters (30 Days)
True 1
paul 1
Page 15 of 16 < 1 2 ... 13 14 15 16 >
Topic Options
#37761 - 03/09/11 10:18 AM Re: Orion, Mission to Alpha Centauri [Re: paul]
kallog Offline
Megastar

Registered: 03/17/10
Posts: 1100
Originally Posted By: paul
and the air that actually touches the walls is probably only around .005 percent of the volume of air that leaves the air tank.

Sure. But I said that was for a long pipe. If you keep making it longer, the wall friction will keep increasing, while the end cap force will decrease by the same amount. Eventually the wall friction will dominate.


Quote:
Quote:
further than the length of the pipe.

and one more thing , if the air is released very slowly
the pipe could actually travel several times its lenght before the air tank empties or equalizes.


However you do it, after the pipe has traveled its length, there's no possibility that any of the air could still be going in the same direction it was when it left the tank, without having turned around at some point. That's where the length-of-pipe limit comes from. Just try to draw a picture of that, it's geometrically impossible!

The slower you release the air, the more mass is left in the tank while you're trying to accelerate it, so the less distance it can go before the released air _has to_ change direction. This reduces the length-of-pipe limit. The length-of-pipe limit can only be approached when the mass of the released air is much higher than that of the pipe and any un-released air.

Top
.
#37771 - 03/09/11 07:18 PM Re: Orion, Mission to Alpha Centauri [Re: kallog]
paul Offline
Megastar

Registered: 03/21/06
Posts: 4136
Quote:
If you keep making it longer, the wall friction will keep increasing, while the end cap force will decrease by the same amount. Eventually the wall friction will dominate.


I didnt make it longer its 500 ft , let me check , brb

---- time passes ----

yep it was 500 ft from the begining

post #34663

Originally Posted By: paul
I think thats a load !!!

if I have a nozzle at one end of a long pipe and the entire pipe
is at 14.7 psi.

lets say the pipe is 60 inch diameter and 500 ft long.


Quote:
Eventually the wall friction will dominate.


the wall friction might dominate between the wall friction and the force felt by the pipe end as a small force that would subtract from the larger force that is generated as the compressed air exits the air tank and passes through the nozzle.

but the resulting force is why the pipe keeps moving.

Quote:
However you do it, after the pipe has traveled its length, there's no possibility that any of the air could still be going in the same direction it was when it left the tank, without having turned around at some point. That's where the length-of-pipe limit comes from. Just try to draw a picture of that, it's geometrically impossible!


that really makes no sence at all.

if i allow a burst of air to excape the tank the pipe would begin to move.

and there is nothing to stop the pipe from moving.

if I wait until the pipe has traversed its lenght and again allow another burst the pipe will accelerate even faster
and I could repeat this until the air in the air tank equalized with the air in the pipe.


Quote:
it's geometrically impossible!


true , which causes the single directional force of the air leaving the nozzle to be the dominant force when determining which force is the greatest force that would give momentum to the pipe.







Edited by paul (03/09/11 07:44 PM)
_________________________
3/4 inch of dust build up on the moon in 4.527 billion years,LOL and QM is fantasy science.

Top
#37773 - 03/10/11 02:24 PM Re: Orion, Mission to Alpha Centauri [Re: paul]
kallog Offline
Megastar

Registered: 03/17/10
Posts: 1100
If the pipe travels its length, then obviously none the air in it can remain where it was. Or it would become outside the pipe, left behind floating in space. So any air that was going in the opposite direction to the pipe has to change direction. That imparts a force to the pipe pushing it backwards.

There really is no way to make progress on this without either:
- Using the law of conservation of momentum or
- Working it out in more detail without giving up just before you get to the solution.

Claims of "there's nothing to stop it" have no value, because they're just claims without reasons.


Edited by kallog (03/10/11 02:25 PM)

Top
#37774 - 03/10/11 11:39 PM Re: Orion, Mission to Alpha Centauri [Re: kallog]
paul Offline
Megastar

Registered: 03/21/06
Posts: 4136
Quote:
If the pipe travels its length, then obviously none the air in it can remain where it was.


I never said that the air would stay where it was.

the majority of the air moves from the air tank to the pipe.

Quote:
So any air that was going in the opposite direction to the pipe has to change direction. That imparts a force to the pipe pushing it backwards.


I agree that the air will be changing direction inside the pipe as the air settles inside the pipe.

but the forces that the air will impart to the pipe during the settling process will not all be in the direction
that would slow the pipe.

the air will apply the same force to the front of the pipe as it will the end of the pipe but most of this force will be to the sides of the pipe.

in other words the negative forces and the positive forces that the air leaving the nozzle applies to the pipe will cancel each other out.

leaving the force generated by the nozzle as the dominate force.

I think there is an easy way to settle this using a experiment.

using pvc pipe and a couple of valves compressed air and water.

and a swimming pool in place of outer space.

releasing the water that is being compressed by air through a pipe that connects to another much larger pipe , should
provide enought visual evidence.
















Edited by paul (03/10/11 11:53 PM)
_________________________
3/4 inch of dust build up on the moon in 4.527 billion years,LOL and QM is fantasy science.

Top
#37781 - 03/12/11 05:01 AM Re: Orion, Mission to Alpha Centauri [Re: paul]
kallog Offline
Megastar

Registered: 03/17/10
Posts: 1100
Originally Posted By: paul

but the forces that the air will impart to the pipe during the settling process will not all be in the direction
that would slow the pipe.

Sure. But on average they will be in the same direction. It's easy to imagine a random cloud of gas that just disperses in all directions the same. But this isn't like that, the entire cloud of gas starts off moving in one specific direction. It doesn't just forget that it was moving backwards rather than forwards.



Quote:
using pvc pipe and a couple of valves compressed air and water.

and a swimming pool in place of outer space.

Excellent idea, and extremely practical and doable. Go for it. You could use an ordinary PVC toilet pipe as the main pipe and a coke bottle water rocket as the tank. Then the valve can just be a pull-string operated flap in the cap of the coke bottle.

If it doesn't work in a pool, put the same device on a wheels or ice-cubes.

Top
#37783 - 03/12/11 05:50 AM Re: Orion, Mission to Alpha Centauri [Re: kallog]
paul Offline
Megastar

Registered: 03/21/06
Posts: 4136
how about just a inflated balloon and a larger un-inflated balloon or a trash bag with a drinking straw between them?

you could pinch off the straw to keep the pressurized air in the inflated balloon.

and if it moves when you release the straw because the air is moving into the bigger balloon or trash bag then that should be good enough.

and really cheap.

we all know that if you blow up a balloon it will fly away if you release it.

without actually doing this simple experiment I can already
say that I believe it will move , and quickly.



Edited by paul (03/12/11 06:03 AM)
_________________________
3/4 inch of dust build up on the moon in 4.527 billion years,LOL and QM is fantasy science.

Top
#37784 - 03/12/11 04:00 PM Re: Orion, Mission to Alpha Centauri [Re: paul]
kallog Offline
Megastar

Registered: 03/17/10
Posts: 1100
Originally Posted By: paul
how about just a inflated balloon and a larger is moving into the bigger balloon or trash bag then that should be good enough.


Believe it or not, I actually did this just now! And it didn't work! I used an emptied pen tube instead of a straw. I tried it with the pen attached to the balloon and it flew along a bit, but much slower than a normal balloon. Then I did it with a very lightweight loose plastic bag on the other end of the pen, and it just dropped to the floor while it was deflating. Absolutely no forward motion!



Quote:

without actually doing this simple experiment I can already
say that I believe it will move , and quickly.


Form your belief after seeing the evidence, not before! If you don't trust my experiment then improve on it. Maybe the mass of the bag stopped it flying away, so tie the screwed up bag to the side of the open straw and see if it also doesn't fly away. Maybe the back pressure from the bag slowed the balloon's deflation. So measure the time compared to doing it with no bag.

Top
#37787 - 03/12/11 07:31 PM Re: Orion, Mission to Alpha Centauri [Re: kallog]
paul Offline
Megastar

Registered: 03/21/06
Posts: 4136
all I can say to your experiment is ...

how much did the empty pen tube weigh?

and how large was the smallest portion where air could pass through it.

it doesnt look like you blew the balloon up very much at all judging from the amount of air in the bag...

try the same with a lighter straw and see what happens.
please dont use a coffee stirring straw.

and one more thing you might try using a string attached to the ceiling of your room and also attached to the tube.

and instead of expecting it to move upward against gravity just see if it will move horizontaly.

I bet it does.


_________________________
3/4 inch of dust build up on the moon in 4.527 billion years,LOL and QM is fantasy science.

Top
#37792 - 03/13/11 03:35 AM Re: Orion, Mission to Alpha Centauri [Re: paul]
kallog Offline
Megastar

Registered: 03/17/10
Posts: 1100
Originally Posted By: paul
all I can say to your experiment is ...


This experiment should put the matter to rest for good. I won't repeat because I know you'll never trust my results, no matter how many adjustments I make at your request. You have to see it with your own eyes.

If you haven't done it by tomorrow I expect a good reason why not! Don't say it was too rainy to go across town to the balloon shop, just do it! Remember, if this is true then the world stands to gain enormously. You have a social responsibility to make it known.

Also, make sure that before you do the experiment, you know what conclusion you can draw from whatever result it might have. It's no use trying it, and it doesn't work, so you say "oh there's some elusive effect I can't correct for, so no conclusion".

Use controls to eliminate concerns about direction, tube diameter, weight, etc. Repeat it with different balloons and after having blown them up and deflated them several times because they become looser with repeated use. Control every factor that might become an excuse to ignore the result.

By the way, it's quite inconvenient trying to attach the inflated balloon to the tube. See if you can find some other kind of tube that can be closed off but won't collapse under the force of the balloon tightened over it. Maybe use a pen tube with a cap on it, inside the plastic bag. Then you can pop the cap off through the bag.


Edited by kallog (03/13/11 03:46 AM)

Top
#37794 - 03/13/11 04:28 AM Re: Orion, Mission to Alpha Centauri [Re: kallog]
paul Offline
Megastar

Registered: 03/21/06
Posts: 4136
Im thinking of using one of the long balloons that can be
used to make animal shapes with.

put part of a plastic drinking straw inside the balloon
and then roll 1/4 of the balloon back over the other 3/4 of the balloon then glue the balloon to the straw , allow the glue to dry , and maybe put a little tape around the tube area to keep the balloon from pulling away from the straw when I release the air through the straw , and keeping the straw pinched off I will blow up the end that is only 1/4 the balloons length and twist the balloon where the straw is to keep the air from going through the straw , then tie the balloon off.

then I will stretch the 3/4 of the balloon that is not inflated to limber it up.

then let it fly.

but this might not work because the air will be blowing up the other 3/4 of the balloon which will subtract from the force , so then I will probably try to find a long narrow plastic bag to use that can contain the volume of air that will be inside the inflated balloon.

either way I wont be finished by tomorrow because the stores are mostly closed and I wont walk inside a wallmart.







Edited by paul (03/13/11 04:39 AM)
_________________________
3/4 inch of dust build up on the moon in 4.527 billion years,LOL and QM is fantasy science.

Top
#37815 - 03/14/11 06:08 PM Re: Orion, Mission to Alpha Centauri [Re: paul]
paul Offline
Megastar

Registered: 03/21/06
Posts: 4136
well , found some of the long balloons but they are so cheaply made that they burst before they can be fully inflated.

I will most likely have to try and find some of the thicker material balloons that wont burst so easily.

and since I refuse to be a part of americas destruction by entering a wallmart , I will have to wait until I can find an american made balloon that isnt so cheaply made that will work.

if thats possible.
_________________________
3/4 inch of dust build up on the moon in 4.527 billion years,LOL and QM is fantasy science.

Top
#37816 - 03/14/11 06:40 PM Re: Orion, Mission to Alpha Centauri [Re: paul]
paul Offline
Megastar

Registered: 03/21/06
Posts: 4136


its amazing that there is still a manufacturer in america.

thank goodness

well the above web site has 3 ft , 6ft even 8 ft balloons.

but I've decided to use 2 empty coleman propane cylinders.

and connect them together and fill one with compressed air
and put a valve in between the two.

they will float on water and they should move because of the air equalizing.






Edited by paul (03/14/11 06:42 PM)
_________________________
3/4 inch of dust build up on the moon in 4.527 billion years,LOL and QM is fantasy science.

Top
#37820 - 03/15/11 01:52 PM Re: Orion, Mission to Alpha Centauri [Re: paul]
kallog Offline
Megastar

Registered: 03/17/10
Posts: 1100
Originally Posted By: paul
its amazing that there is still a manufacturer in america.

Hehe, I'm surprised too :P

Quote:

but I've decided to use 2 empty coleman propane cylinders.

and connect them together and fill one with compressed air
and put a valve in between the two.

they will float on water and they should move because of the air equalizing.


Fantastic! The rigid outside shape will make it much more conclusive by preventing any aerodynamic effects of the expanding bag/etc. Do you already have the gear to build it?

Top
#37826 - 03/16/11 02:57 AM Re: Orion, Mission to Alpha Centauri [Re: paul]
Amaranth Rose II Offline

Superstar

Registered: 12/16/06
Posts: 962
Loc: Southeast Nebraska, USA
I understand your frustration with the long balloons. Having made a bunch of balloon animals, I discovered that if you stretch them lengthwise several times before you inflate them they don't burst so bad. It exercises the rubber and makes it more flexible so they don't burst. I went through a few balloons myself before I discovered this. Good luck with the propane cylinders, and remember even an empty one still has a volume of propane in it, so be careful.
_________________________
If you don't care for reality, just wait a while; another will be along shortly. --A Rose


Top
#37837 - 03/16/11 06:46 PM Re: Orion, Mission to Alpha Centauri [Re: Amaranth Rose II]
paul Offline
Megastar

Registered: 03/21/06
Posts: 4136
Rose

I went through several myself and I can imagine what entertainers are going through with the cheaply made chinese balloons , but you get what you pay for and in a republican controlled economy there is no end in sight of cheap.

even the chinese businessmen are moving their businesses to africa where even cheaper labor is available.

and thanks for the warning.
_________________________
3/4 inch of dust build up on the moon in 4.527 billion years,LOL and QM is fantasy science.

Top
#37840 - 03/16/11 10:24 PM Re: Orion, Mission to Alpha Centauri [Re: paul]
kallog Offline
Megastar

Registered: 03/17/10
Posts: 1100
Originally Posted By: paul
Rose
I went through several myself and I can imagine what entertainers are going through with the cheaply made chinese balloons , but you get what you pay for and in a republican


As the only one who did this experiment successfully, without a single balloon failure, I have to say mine was (I only needed one and reused it!) Chinese made, and I got it from Walmart. Maybe there's a reason everybody buys that stuff wink

Top
#37846 - 03/17/11 01:05 PM Re: Orion, Mission to Alpha Centauri [Re: kallog]
Bill S. Offline
Megastar

Registered: 08/20/10
Posts: 3570
Loc: Essex, UK
[quote=K]I got it from Walmart.[quote]

Are you allowed to advertise on this Forum?


BTW, Kallog, Iíve lost track of the thread in which you asked what a libertarian was, so Iím going to slip it in here in deference to the links between politics and sci-fi.

Iím not as politically orientated as my son, so treat my answer with caution. I understand it has to do with supporting unrestricted trade, no subsidies or anything like that, and a belief that we all get what we deserve. If we are poor, itís because we failed to take the opportunities we should have grabbed, so itís our own fault.

I was going to say ďevery man for himselfĒ but Iím sure that's politically incorrect, these days. Somehow, ďevery person for itselfĒ doesnít have the same ring to it, though!
_________________________
There never was nothing.

Top
#37859 - 03/18/11 08:12 PM Re: Orion, Mission to Alpha Centauri [Re: kallog]
paul Offline
Megastar

Registered: 03/21/06
Posts: 4136
Quote:
As the only one who did this experiment successfully


I still dont think that you inflated your balloon enough

its obvious that if you would have inflated the balloon properly the plastic bag would have been bigger or looked as
if it was filled with pressurized air from the balloon.

if you would have used an american made balloon the experiment might have worked because you could have blown it up much more than the cheap chinese balloon you used.




_________________________
3/4 inch of dust build up on the moon in 4.527 billion years,LOL and QM is fantasy science.

Top
#37868 - 03/19/11 02:47 AM Re: Orion, Mission to Alpha Centauri [Re: Bill S.]
kallog Offline
Megastar

Registered: 03/17/10
Posts: 1100
Originally Posted By: Bill S.
If we are poor, itís because we failed to take the opportunities we should have grabbed, so itís our own fault.


OK yea I guess I am, or rather I'd like a world where that worked. It isn't so good in reality when you have nepotism and all that.

Top
#37869 - 03/19/11 02:53 AM Re: Orion, Mission to Alpha Centauri [Re: paul]
kallog Offline
Megastar

Registered: 03/17/10
Posts: 1100
Originally Posted By: paul
I still dont think that you inflated your balloon enough

As I already said, I tried it without the bag. I used the same amount of inflation in both cases. So it was enough, because it did travel without the bag.

But you are kind of right, I was afraid to blow it up too much because it was the last good balloon I had left and I didn't want it to break :P

Anyway! That took me 10 minutes one evening. Why are you still unable to do anything at all? What's causing these endless delays? Have you got the filler valve yet? Have you just got some round balloons like I used? Do it yourself!!!

It doesn't have to be fancy, just get a normal balloon, a plastic bag, a pen tube, some tape, and a rubber band. That's all you need to shatter the world of physics and get a Nobel prize!!! Do it!

You can also use a condom. Those are made to higher quality standards and are more readily available than balloons, and can be inflated further. In fact it would probably be more effective because of the bigger opening.


Edited by kallog (03/19/11 03:03 AM)

Top
Page 15 of 16 < 1 2 ... 13 14 15 16 >



Newest Members
debbieevans, bkhj, jackk, Johnmattison, RacerGT
865 Registered Users
Sponsor
Facebook

We're on Facebook
Join Our Group

Science a GoGo's Home Page | Terms of Use | Privacy Policy | Contact Us
Features | News | Books | Physics | Space | Climate Change | Health | Technology | Natural World

Copyright © 1998 - 2016 Science a GoGo and its licensors. All rights reserved.