Help me with this real life story problem

Science > Physics > Help me with this real life story problem

LINK TO THIS PAGE

rating : 0 | 0

Page 1 of 1

Topic:	Science > Physics
User:	""
Date:	25 Aug 2005 03:07:41 PM
Object:	Help me with this real life story problem

I had physics in High School, and remember enough to know this is a
solveable problem, but don't remember how to do it.. anyone kind enough
to solve it for me?
I want to float a big surplus weather balloon in front of my church as
a decoration for an upcoming dance. I need to know if I can do it in
my budget.
If I can pull this off, I will buy a weather balloon that I saw on the
internet. How much helium would I need to buy to float it, just 10 or
20 feet off the ground.
Lets say, for out purposes the balloon, rope and sign displayed on it
weigh about 2 kg. Fully inflated the balloon is about 15 feet in
diameter. Doing rough calculation here, ignore the fact that it is not
a perfect sphere, assume it is.
How many cubit feet of helium would I have to purchase to get it up?
Don't need any lifting power, and would be happy to put just enough
helium in to lift balloon & sign, filling rest with ambient air.
Any rough guesses on how many cubic feet of helium I would need? Just
something in the neighborhood so I can know if this is remotely
possible with my budget.. will call welding place once I get rough
notion of how much I would need, and get quote on gas..
.

User: "Richard Henry"
Title: Re: Help me with this real life story problem	25 Aug 2005 03:47:13 PM

<jackjohansson@gmail.com> wrote in message
news:1125000460.970994.105720@f14g2000cwb.googlegroups.com...

I had physics in High School, and remember enough to know this is a
solveable problem, but don't remember how to do it.. anyone kind enough
to solve it for me?

I want to float a big surplus weather balloon in front of my church as
a decoration for an upcoming dance. I need to know if I can do it in
my budget.

If I can pull this off, I will buy a weather balloon that I saw on the
internet. How much helium would I need to buy to float it, just 10 or
20 feet off the ground.

Lets say, for out purposes the balloon, rope and sign displayed on it
weigh about 2 kg. Fully inflated the balloon is about 15 feet in
diameter. Doing rough calculation here, ignore the fact that it is not
a perfect sphere, assume it is.

How many cubit feet of helium would I have to purchase to get it up?
Don't need any lifting power, and would be happy to put just enough
helium in to lift balloon & sign, filling rest with ambient air.

Any rough guesses on how many cubic feet of helium I would need? Just
something in the neighborhood so I can know if this is remotely
possible with my budget.. will call welding place once I get rough
notion of how much I would need, and get quote on gas..

The Dalton number (proportional to density for gases) for air is about
29-30, since it is mostly a mix of nitrogen (28) and oxygen (32). For
helium the Dalton number is 4. Lift is proportional to the Dalton-number
difference multiplied by the volume.
As a complication, the helium in the balloon will be slightly above
atmospheric pressure in order to inflate the balloon to its full shape.
.

User: "Androcles Androcles@ MyPlace.org"
Title: Re: Help me with this real life story problem	25 Aug 2005 05:59:08 PM

<jackjohansson@gmail.com> wrote in message
news:1125000460.970994.105720@f14g2000cwb.googlegroups.com...
|I had physics in High School, and remember enough to know this is a
| solveable problem, but don't remember how to do it.. anyone kind
enough
| to solve it for me?
|
| I want to float a big surplus weather balloon in front of my church as
| a decoration for an upcoming dance. I need to know if I can do it in
| my budget.
|
| If I can pull this off, I will buy a weather balloon that I saw on the
| internet. How much helium would I need to buy to float it, just 10 or
| 20 feet off the ground.
None. Use a fan and let it run, or rent a bouncy castle.
Androcles.
|
| Lets say, for out purposes the balloon, rope and sign displayed on it
| weigh about 2 kg. Fully inflated the balloon is about 15 feet in
| diameter. Doing rough calculation here, ignore the fact that it is
not
| a perfect sphere, assume it is.
|
| How many cubit feet of helium would I have to purchase to get it up?
| Don't need any lifting power, and would be happy to put just enough
| helium in to lift balloon & sign, filling rest with ambient air.
|
| Any rough guesses on how many cubic feet of helium I would need?
Just
| something in the neighborhood so I can know if this is remotely
| possible with my budget.. will call welding place once I get rough
| notion of how much I would need, and get quote on gas..
|
.

User: ""
Title: Re: Help me with this real life story problem	25 Aug 2005 11:41:16 PM

Androcles wrote:

You see a lot of fan-driven, PVC-inflatables in China.
They are kept inflated with small motors,
and many of them have moving parts
such as waving arms.
These are cheap and very effective for attracting attention.
A moving inflatable with an internal Light System
can be very dramatic at night.
A Google image search on
"air puppet"
will find sites selling and renting these.
The web site below shows some examples of inflatable with moving parts.
As can be seen, there are units that reach heights of 40 feet or more.
http://www.balloonco.com
--
Tom Potter
http://home.earthlink.net/~tdp
http://photos.yahoo.com/tdp1001
http://tom-potter.blogspot.com
.

User: "Martin Hogbin"
Title: Re: Help me with this real life story problem	25 Aug 2005 05:32:05 PM

<jackjohansson@gmail.com> wrote in message news:1125000460.970994.105720@f14g2000cwb.googlegroups.com...

I had physics in High School, and remember enough to know this is a
solveable problem, but don't remember how to do it.. anyone kind enough
to solve it for me?

I want to float a big surplus weather balloon in front of my church as
a decoration for an upcoming dance. I need to know if I can do it in
my budget.

If I can pull this off, I will buy a weather balloon that I saw on the
internet. How much helium would I need to buy to float it, just 10 or
20 feet off the ground.

Lets say, for out purposes the balloon, rope and sign displayed on it
weigh about 2 kg. Fully inflated the balloon is about 15 feet in
diameter. Doing rough calculation here, ignore the fact that it is not
a perfect sphere, assume it is.

How many cubit feet of helium would I have to purchase to get it up?
Don't need any lifting power, and would be happy to put just enough
helium in to lift balloon & sign, filling rest with ambient air.

Any rough guesses on how many cubic feet of helium I would need?

Very roughly you will need 2 m^3 which is about 20 cubic feet.
Martin Hogbin
.

User: "Uncle Al"
Title: Re: Help me with this real life story problem	25 Aug 2005 05:32:05 PM

wrote:

1) Boyancy is one gram/liter helium contained.
2) Volume = (4(pi)r^3)/3
3) Balloon helium contains a lot of air on purpose.
4) 1 ft^3 = 28.3 liters

Lets say, for out purposes the balloon, rope and sign displayed on it
weigh about 2 kg. Fully inflated the balloon is about 15 feet in
diameter. Doing rough calculation here, ignore the fact that it is not
a perfect sphere, assume it is.

How many cubit feet of helium would I have to purchase to get it up?
Don't need any lifting power, and would be happy to put just enough
helium in to lift balloon & sign, filling rest with ambient air.

Any rough guesses on how many cubic feet of helium I would need? Just
something in the neighborhood so I can know if this is remotely
possible with my budget.. will call welding place once I get rough
notion of how much I would need, and get quote on gas..

1) Boyancy is one gram/liter helium contained.
2) Volume = [4(pi)r^3]/3
3) Balloon helium contains a lot of air on purpose.
4) 1 ft^3 = 28.3 liters
Remember the weight of the tether. If it is going to be up for a
while,
http://www.hi-float.com/
and include that weight, too. Might as well hoist a Cyalume stick,
too.
--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf
.

User: "Quantum Mirror"
Title: Re: Help me with this real life story problem	26 Aug 2005 12:27:27 AM

wrote:

I had physics in High School, and remember enough to know this is a
solveable problem, but don't remember how to do it.. anyone kind enough
to solve it for me?

I want to float a big surplus weather balloon in front of my church as
a decoration for an upcoming dance. I need to know if I can do it in
my budget.

If I can pull this off, I will buy a weather balloon that I saw on the
internet. How much helium would I need to buy to float it, just 10 or
20 feet off the ground.

Lets say, for out purposes the balloon, rope and sign displayed on it
weigh about 2 kg. Fully inflated the balloon is about 15 feet in
diameter. Doing rough calculation here, ignore the fact that it is not
a perfect sphere, assume it is.

How many cubit feet of helium would I have to purchase to get it up?
Don't need any lifting power, and would be happy to put just enough
helium in to lift balloon & sign, filling rest with ambient air.

Any rough guesses on how many cubic feet of helium I would need? Just
something in the neighborhood so I can know if this is remotely
possible with my budget.. will call welding place once I get rough
notion of how much I would need, and get quote on gas..

I think for a church, the local airgas distributor would float the
balloon for a little advertising!
.

User: "Randy Poe"
Title: Re: Help me with this real life story problem	25 Aug 2005 03:48:51 PM

wrote:

I had physics in High School, and remember enough to know this is a
solveable problem, but don't remember how to do it.. anyone kind enough
to solve it for me?

No, but I'll give you some equations to work with.

I want to float a big surplus weather balloon in front of my church as
a decoration for an upcoming dance. I need to know if I can do it in
my budget.

If I can pull this off, I will buy a weather balloon that I saw on the
internet. How much helium would I need to buy to float it, just 10 or
20 feet off the ground.

You want it so that it just hovers, untethered, about
10-20 feet off the ground? Where it hovers will vary
with the barometric pressure.
Better to do what the florists do: give it enough He so
it tugs upward against the rope, and needs a little
weight to hold it down.

Here's the basic calculation: Buoyant force = weight
(mg) of air displaced by balloon = g*density of air*
volume of balloon.
[Note: There's a continuing argument on this NG as to whether
"weight" means mg or can be legitimately used for m. For
this calculation, I'll confine it to mg]
Net upward force = Buoyant force - weight of balloon
(including contained gases).
The density of helium is about 0.18 kg/m^3, and the
density of air is in the neighborhood of 1.2 kg/m^3
(again, this depends on the barometric pressure, also
on the humidity and temperature).
Let's say you have a mix of p% helium and (1-p)% air.
Then the density of your gas mixture is
0.18*p + 1.2*(1-p)
and the weight of your inflated balloon is
g*[(0.18*p + 1.2*(1-p))*V + M]
where M = mass of empty balloon and any payload (rope, weights,
etc) and V = volume of balloon in m^3 = (4/3)*pi*r^3.
The buoyant force is g*1.2*V.
So the net lift is going to be
g*1.2*V - g*[(0.18*p + 1.2*(1-p))*V + M]
= g*[1.2*V - 0.18*p*V - 1.2*(1-p)*V - M]
= g*[(1.2-0.18)*p*V - M]

Any rough guesses on how many cubic feet of helium I would need? Just
something in the neighborhood so I can know if this is remotely
possible with my budget.. will call welding place once I get rough
notion of how much I would need, and get quote on gas..

You'll get neutral buoyancy, zero net lift, if the expression
in brackets [ ] is zero, which means
(1.2-0.18)*p*V = M
p = M/(1.02*V) ~ about M/V (if M is in kg, V in m^3).
Well, that's surprisingly simple. I wonder if I goofed in
my algebra.
You said the diameter is 15 ft (4.6 m) so the radius is
2.3 ft and the volume is 51 m^3. If the total payload is
only 2 kg, then M/V = 0.04 and you need only 4% of the 51
m^3 to be helium for neutral buoyancy, maybe a couple of
times that for a decent amount of lift.
If I were you, I'd buy enough to do at least one test flight.
- Randy
.

User: "CWatters"
Title: Re: Help me with this real life story problem	25 Aug 2005 04:01:51 PM

"Randy Poe" <poespam-trap@yahoo.com> wrote in message
news:1125002931.891322.297820@g43g2000cwa.googlegroups.com...

If I were you, I'd buy enough to do at least one test flight.

and I were you I'd use a bit more helium and a rope to tie it down.
.

User: "Richard Henry"
Title: Re: Help me with this real life story problem	25 Aug 2005 04:37:59 PM

"CWatters" <colin.watters@pandoraBOX.be> wrote in message
news:3lqPe.178465$nr7.9795727@phobos.telenet-ops.be...

"Randy Poe" <poespam-trap@yahoo.com> wrote in message
news:1125002931.891322.297820@g43g2000cwa.googlegroups.com...

If I were you, I'd buy enough to do at least one test flight.

and I were you I'd use a bit more helium and a rope to tie it down.

Unless the balloon is very elastic, adding more helium than is needed to
bring it to full size will just reduce the lift.
.

User: "Uncle Al"
Title: Re: Help me with this real life story problem	25 Aug 2005 05:33:17 PM

Randy Poe wrote:

jackjohansson@gmail.com wrote:

I had physics in High School, and remember enough to know this is a
solveable problem, but don't remember how to do it.. anyone kind enough
to solve it for me?

No, but I'll give you some equations to work with.

You want it so that it just hovers, untethered, about
10-20 feet off the ground? Where it hovers will vary
with the barometric pressure.

Better to do what the florists do: give it enough He so
it tugs upward against the rope, and needs a little
weight to hold it down.

Here's the basic calculation: Buoyant force = weight
(mg) of air displaced by balloon = g*density of air*
volume of balloon.

[Note: There's a continuing argument on this NG as to whether
"weight" means mg or can be legitimately used for m. For
this calculation, I'll confine it to mg]

Net upward force = Buoyant force - weight of balloon
(including contained gases).

The density of helium is about 0.18 kg/m^3, and the
density of air is in the neighborhood of 1.2 kg/m^3
(again, this depends on the barometric pressure, also
on the humidity and temperature).

Let's say you have a mix of p% helium and (1-p)% air.
Then the density of your gas mixture is
0.18*p + 1.2*(1-p)
and the weight of your inflated balloon is
g*[(0.18*p + 1.2*(1-p))*V + M]

where M = mass of empty balloon and any payload (rope, weights,
etc) and V = volume of balloon in m^3 = (4/3)*pi*r^3.

The buoyant force is g*1.2*V.

So the net lift is going to be

g*1.2*V - g*[(0.18*p + 1.2*(1-p))*V + M]

= g*[1.2*V - 0.18*p*V - 1.2*(1-p)*V - M]

= g*[(1.2-0.18)*p*V - M]

You'll get neutral buoyancy, zero net lift, if the expression
in brackets [ ] is zero, which means

(1.2-0.18)*p*V = M

p = M/(1.02*V) ~ about M/V (if M is in kg, V in m^3).

Well, that's surprisingly simple. I wonder if I goofed in
my algebra.

You said the diameter is 15 ft (4.6 m) so the radius is
2.3 ft and the volume is 51 m^3. If the total payload is
only 2 kg, then M/V = 0.04 and you need only 4% of the 51
m^3 to be helium for neutral buoyancy, maybe a couple of
times that for a decent amount of lift.

If I were you, I'd buy enough to do at least one test flight.

- Randy

There are times when one is better off with a chemist than a
physicist. "8^>)
--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf
.

Page 1 of 1

Post reply

bicycle question - real life event
Shallow geothermics in real life...
Catholic Bishop: 9-11 Was Inside Job - Destroying America - I HATEbush just like any real man would - demand Justice for Humanity - Why wouldGOD will the destruction of life for a criminal thief? - We, as the People,demand you allow US, the human spe
REAL Time-Travellers!!
Re: Fantastic Flying 757 Engine was Re: The Ultimate Pentagon 9/11 Question Andy Carol couldn't answer. was Re: Flight 175 WAS a FUEL TANKER, for REAL. This is not a "theory".
The real effect of centrifugal force
REAL ALCHEMY in BIOLOGY
Gamma Ray Bursts -- REAL CAUSE of

Now Here's a REAL Miracle! -- Pope John XXIII....
Re: How do I short the real estate bubble?
Article: Theoretical Physics - On Physics and the Real World
Yes, REAL suspected Black Holes can RiP you APART.!! But NOT in GR gtr Tivity.!! Because in GR Tivity you would be a POiNT ..and if you COULD have a mass, in GR, you would be a POiNT-mass. POiNT-mass CANNOT *STRETCH* with TOP & BOTTOM ROCKETs attache
No Mass -- no real physics !!
$ All sub-SYSTEMs have "surroundings", duh. Sub-SYSTEMs are "submerged" in SYSTEM "working fluid" AMBiENT. Sub-SYSTEMs ONLY EXCHANGE energy with "working fluid" AMBiENT. Go-go Google GROUP SEARCH: < My BiGGER bang > ..My REAL STUFF. TOTAL La
H-atom wavefunctions: real or imaginary?

NEWER

pg.1612 pg.1232 pg.940 pg.716 pg.544 pg.412 pg.311 pg.234 pg.175 pg.130 pg.96 pg.70 pg.50 pg.35 pg.24 pg.16 pg.10 pg.6 pg.3 pg.1

OLDER