Anyone know offhand without going to too much trouble, what is the ratio
for volume of helium to lbs force against gravity ?

Fred

A cubic foot of air at sea level under standard conditions weighs
about 0.077 lb, so if you displaced that cubic foot of air with
helium, the net lifting force would be slightly less than that (i.e.,
0.077 lb minus the weight of a cubic foot of helium, which I don't
know the value of offhand). Of course, you also have to subtract the
weight of the container.

Bert

ff wrote:

Anyone know offhand without going to too much trouble, what is the ratio
for volume of helium to lbs force against gravity ?

Fred

Sounds like another budding lawn chair pilot in the making.

I'm not sure but the simple way would be to get a 4oz fishing weight and see
how many balloons you need to lift it and multiply this by 4.

Saturday mornings at auto dealerships they usually have a whole lot of
balloons they might let you play with.

--
Roger Shoaf
If you are not part of the solution, you are not dissolved in the solvent.


"ff" wrote in message
...
Anyone know offhand without going to too much trouble, what is the ratio
for volume of helium to lbs force against gravity ?

Fred

I believe a cubic foot of helium will lift about 28.2 grams. Multiply
the volume times 28 and divide by 448 g/lb.

A 10' diameter weather balloon will lift about 32 pounds.

ff wrote:
Anyone know offhand without going to too much trouble, what is the ratio
for volume of helium to lbs force against gravity ?

Fred



--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

On Sun, 20 Jul 2003 05:16:09 GMT, ff wrote:

Anyone know offhand without going to too much trouble, what is the ratio
for volume of helium to lbs force against gravity ?

A Google.com search on:

helium lift cubic foot

....found more than one thousand, three hundred
web pages with the information you want.
No trouble at all.

--
--Pete
"Peter W. Meek"
http://www.msen.com/~pwmeek/

On Sun, 20 Jul 2003 05:16:09 GMT, ff wrote:

,;Anyone know offhand without going to too much trouble, what is the ratio
,; for volume of helium to lbs force against gravity ?

I don't think there is an answer to your question but...

I think you are asking about Archimedes principle...

All bodies floating on or submerged in a fluid are buoyed up by a
force exactly equal to the weight of the fluid they displace.

1 cubic foot of air= 0.0807 pounds at 32 F and 1 atm.

1 cubic foot of helium= 0.0111 (same conditions)

If you are planning a trip in a lawn chair that should provide the
needed information.

On Sun, 20 Jul 2003 05:16:09 GMT, ff wrote:

Anyone know offhand without going to too much trouble, what is the ratio
for volume of helium to lbs force against gravity ?

Fred

I am unable to resist.

Anyone know offhand without going to too much trouble, what is the
ratio for volume of helium to lbs force against gravity ?

YES


Errol Groff
Instructor, Machine Tool Department
H.H. Ellis Tech
613 Upper Maple Street
Danielson, CT 06239

860 774 8511 x1811

http://pages.cthome.net/errol.groff/

http://newenglandmodelengineeringsociety.org/

In article ,
Don Wilkins wrote:
On Sun, 20 Jul 2003 05:16:09 GMT, ff wrote:

,;Anyone know offhand without going to too much trouble, what is the ratio
,; for volume of helium to lbs force against gravity ?

I don't think there is an answer to your question but...

I think you are asking about Archimedes principle...

All bodies floating on or submerged in a fluid are buoyed up by a
force exactly equal to the weight of the fluid they displace.

1 cubic foot of air= 0.0807 pounds at 32 F and 1 atm.

1 cubic foot of helium= 0.0111 (same conditions)

And -- of course -- one cubic foot of vacuum would lift the full
0.0807 pounds (again at STP), but the trick is finding a rigid container
which doesn't weigh more than the lift. :-)

If you are planning a trip in a lawn chair that should provide the
needed information.

Be sure to file your flight plan. :-)

Enjoy,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

On Mon, 21 Jul 2003 02:05:39 GMT, Jeff Wisnia
wrote:

So what *is* the pressure in a typical rubber party balloon. IIRC, it gets
*lower* as the balloon expands. I think it's the same with soap bubbles.

I suppose the pressure in one of those mylar party balloons must be pretty
close to one atmosphere.

If the sides are not rigid it's always *exactly* atmospheric pressure.
If it expands either atmospheric pressure has dropped or the
temperature of the balloon has gone up.

Here's a question for everyone. Explain *exactly* the mechanics of
how and why a balloon floats :^)? Not as easy as one might think.

And a second one is why when you have a helium balloon in your car and
put the brakes on to stop, the balloon will float to the back of the
car instead of flying to the front like everything else. Again, what
are the mechanics that make it do so?

John

Please note that my return address is wrong due to the amount of junk email I get.
So please respond to this message through the newsgroup.

Errol Groff wrote:

On Sun, 20 Jul 2003 05:16:09 GMT, ff wrote:



Anyone know offhand without going to too much trouble, what is the ratio
for volume of helium to lbs force against gravity ?

Fred



I am unable to resist.

Anyone know offhand without going to too much trouble, what is the
ratio for volume of helium to lbs force against gravity ?

YES




Thank you for sharing that information :-)

For those who were wondering, I'm not going flying in my lawn chair !!
I have some R/C gear and was contemplating building a small blimp or
dirigible. So I was wondering how large it would have to be to carry
motor, battery,
receiver and servos. Anyone ever tried this or seen one?

Fred

"John Flanagan" wrote in message
...
On Mon, 21 Jul 2003 02:05:39 GMT, Jeff Wisnia
wrote:

So what *is* the pressure in a typical rubber party balloon. IIRC, it
gets
*lower* as the balloon expands. I think it's the same with soap bubbles.

I suppose the pressure in one of those mylar party balloons must be
pretty
close to one atmosphere.

If the sides are not rigid it's always *exactly* atmospheric pressure.
If it expands either atmospheric pressure has dropped or the
temperature of the balloon has gone up.

Here's a question for everyone. Explain *exactly* the mechanics of
how and why a balloon floats :^)?

As I understand the physics, air is a fluid and the helium balloon being
lighter than the air around it floats just as a drop of oil will float if
released from the bottom of a volume of water.


Not as easy as one might think.

And a second one is why when you have a helium balloon in your car and
put the brakes on to stop, the balloon will float to the back of the
car instead of flying to the front like everything else. Again, what
are the mechanics that make it do so?

Again the air being heaver than the balloon the air has more mass. When
this mass is in motion, pressure is equal on all sides of the balloon. When
the brakes are applied the air inside the car keeps moving at the speed the
car was going until it hits the windshield. As air bunches up in the front
part of the car, there is more air pressure at the front of the car and less
at the back so the pressure in the front pushes the lighter balloon
backwards.

--
Roger Shoaf
If you are not part of the solution, you are not dissolved in the solvent.

ff wrote in message
...
Errol Groff wrote:

On Sun, 20 Jul 2003 05:16:09 GMT, ff wrote:

Anyone know offhand without going to too much trouble, what is the ratio
for volume of helium to lbs force against gravity ?

Fred

I am unable to resist.

Anyone know offhand without going to too much trouble, what is the
ratio for volume of helium to lbs force against gravity ?

YES


Thank you for sharing that information :-)

For those who were wondering, I'm not going flying in my lawn chair !!
I have some R/C gear and was contemplating building a small blimp or
dirigible. So I was wondering how large it would have to be to carry
motor, battery,
receiver and servos. Anyone ever tried this or seen one?

Never tried one but have seen numerous examples.
Galliger (sp?, he of smashed water melons) used one in his
act for a while.

There are at least a dozen R/C blimps available already. They have been
around for years

(John Flanagan) wrote:

On Mon, 21 Jul 2003 02:05:39 GMT, Jeff Wisnia
wrote:

So what *is* the pressure in a typical rubber party balloon. IIRC, it gets
*lower* as the balloon expands. I think it's the same with soap bubbles.

I suppose the pressure in one of those mylar party balloons must be pretty
close to one atmosphere.

If the sides are not rigid it's always *exactly* atmospheric pressure.

This is not true unless there's a hole in the balloon to allow the
inside and outside pressures to equalize. As long as the balloon is
sealed, the internal pressure can be anywhere from ambient atmospheric
pressure up to the maximum (gauge) pressure the balloon can withstand.
The internal pressure is balanced not only by the external pressure,
but also by stresses in the material of the balloon. The same is true
for basketballs and pneumatic tires.

If it expands either atmospheric pressure has dropped or the
temperature of the balloon has gone up.

This is generally true, but it doesn't mean that the final pressure is
equal to the initial pressure, or that either one is equal to the
ambient atmospheric pressure. The expansion will relieve some of the
increased pressure differential, but not necessarily all of it. The
amount will depend on the stress/strain characteristics of the balloon
material.

Here's a question for everyone. Explain *exactly* the mechanics of
how and why a balloon floats :^)? Not as easy as one might think.

The forces due to gravitational acceleration acting on the mass of air
in the atmosphere results in a vertical pressure gradient (lower
pressure at higher altitudes), which means the pressure acting on the
top part of the balloon is lower than the pressure acting on the
bottom part. Integrating those pressures over the surface of the
balloon gives a net upward force (aka buoyant force). If the weight of
the balloon is less than the buoyant force, the balloon will rise; if
the weight is more than the buoyant force, it will sink; if the weight
is exactly equal to the buoyant force, the balloon will stay where it
is (but it's an unstable equilibrium).

And a second one is why when you have a helium balloon in your car and
put the brakes on to stop, the balloon will float to the back of the
car instead of flying to the front like everything else. Again, what
are the mechanics that make it do so?

The same as above, except that now we're talking about an acceleration
due to braking instead of due to gravity, resulting in a horizontal
pressure gradient instead of a vertical gradient. The balloon's mass
multiplied by this acceleration presumably results in a horizontal
"weight" which is less than the horizontal "buoyant" force, so the
balloon "rises" (i.e., moves in the direction of the acceleration).

Bert

On Sun, 20 Jul 2003 22:58:47 -0700, "Roger Shoaf"
wrote:

As I understand the physics, air is a fluid and the helium balloon being
lighter than the air around it floats just as a drop of oil will float if
released from the bottom of a volume of water.

But, mechanically, "how" does it float. You almost answered it below.

Not as easy as one might think.

And a second one is why when you have a helium balloon in your car and
put the brakes on to stop, the balloon will float to the back of the
car instead of flying to the front like everything else. Again, what
are the mechanics that make it do so?

Again the air being heaver than the balloon the air has more mass. When
this mass is in motion, pressure is equal on all sides of the balloon. When
the brakes are applied the air inside the car keeps moving at the speed the
car was going until it hits the windshield. As air bunches up in the front
part of the car, there is more air pressure at the front of the car and less
at the back so the pressure in the front pushes the lighter balloon
backwards.

It took a little time for a friend and I to realize how a balloon
floats. I think about half a Big Mac at McDonalds one day. You're
correct here. It really puzzled me for awhile when I first noticed
this phenonemen (sp). I have a lot of fun with kids when I tell them
this, they usually go beserk and get real excited when they see it
happen.

The reason why a balloon floats in still air is because of the
pressure gradient between the top and the bottom of the balloon. Most
people don't think there is enough of a gradient to make a balloon
float but there is. They usually think of pressure drops between sea
level and the top of a mountain, not one over just a foot of height.
If the pressure was the same it would sink.

John

Please note that my return address is wrong due to the amount of junk email I get.
So please respond to this message through the newsgroup.

Errol Groff wrote:

On Sun, 20 Jul 2003 05:16:09 GMT, ff wrote:

Anyone know offhand without going to too much trouble, what is the ratio
for volume of helium to lbs force against gravity ?

Fred

I am unable to resist.

Anyone know offhand without going to too much trouble, what is the
ratio for volume of helium to lbs force against gravity ?

YES

That's eggsackly the same answer I give folks who "ask in the negative", as
when they barge in on me with, "You haven't seen Gwendolyn have you?" My
answer is, "YES, I haven't."

Jeff
--
Jeff Wisnia (W1BSV + Brass Rat '57 EE)

"Success is getting what you like; Happiness is liking what you get."






Errol Groff
Instructor, Machine Tool Department
H.H. Ellis Tech
613 Upper Maple Street
Danielson, CT 06239

860 774 8511 x1811

http://pages.cthome.net/errol.groff/

http://newenglandmodelengineeringsociety.org/

Subject: Helium lifting ability
From: Jeff Wisnia
Date: 21/07/03 03:05 GMT Daylight Time
Message-id:

So what *is* the pressure in a typical rubber party balloon. IIRC, it gets
*lower* as the balloon expands. I think it's the same with soap bubbles.

It's higher as the balloon expands or there would be negative work being done
to inflate the balloon against the elasticity of the rubber.


I suppose the pressure in one of those mylar party balloons must be pretty
close to one atmosphere.

It can be anything up to what the material will withstand. It can't be lower
than atmospheric though because the internal and external pressure will
equalise back to atmospheric via a change in volume of the balloon. Once the
balloon (given the relatively inelastic material) has reached its maximum
volume the internal pressure will rise as more gas is pumped in. The lifting
capability will then decrease though as the mass rises for no corresponding
gain in volume and boyancy.

For a balloon made of inelastic material the maximum lift occurs when the
internal pressure is the same as external and the ratio of volume to mass is
highest. i.e. fully inflated until the pressure just starts to rise above
atmospheric. For a balloon made of elastic material the maximum lift also
occurs when the ratio of volume to mass is highest, but the pressure for that
depends on the strength and elasticity of the material.


Dave Baker - Puma Race Engines (www.pumaracing.co.uk)
"How's life Norm?"
"Not for the squeamish, Coach" (Cheers, 1982)

ff wrote:

Errol Groff wrote:

On Sun, 20 Jul 2003 05:16:09 GMT, ff wrote:



Anyone know offhand without going to too much trouble, what is the ratio
for volume of helium to lbs force against gravity ?

Fred



I am unable to resist.

Anyone know offhand without going to too much trouble, what is the
ratio for volume of helium to lbs force against gravity ?

YES




Thank you for sharing that information :-)

For those who were wondering, I'm not going flying in my lawn chair !!
I have some R/C gear and was contemplating building a small blimp or
dirigible. So I was wondering how large it would have to be to carry
motor, battery,
receiver and servos. Anyone ever tried this or seen one?

Fred

These are readilly available. Have been for several years.
Try one of the Indoor Flyer R/C magazines for ad's for these.
http://www.google.ca/search?q=radio+...-1&hl=en&meta=
Above is a link to a google search for radio control airships. About
5000 links. Some are sure to be pertinant. Have fun!

Cheers
Trevor Jones

In article , a
says...
as the balloon expands. I think it's the same with soap bubbles.

It's higher as the balloon expands or there would be negative work being done
to inflate the balloon against the elasticity of the rubber.

I think he meant to say that the differential work done
to inflate the first ten percent is smaller than the
differential work to go from, say, 80 to 90 percent
capacity.

But still net postive everywhere on the curve.

This is pretty obvious if you blow up ballons for a kid's
party. Getting it to start is the toughest!

Jim

==================================================
please reply to:
JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com
==================================================

In article , Jeff says...

Jeeze Jim, do I row up behind you on the pond and splash a paddle into
the water just as you're about to set the hook?

LOL!

I guess I never did like fishing that much.

Jim

==================================================
please reply to:
JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com
==================================================

I thought that MAYBE I actually still had the paper those guys wrote--but no.
Memory sez they did an aluminum geodetic frame covered with sheet aluminum
triangles, all sealed with wax. I don't remember what stopped them--the sheets
or the frame collapsing, or all the joints leaking.

David

"DoN. Nichols" wrote:
A high school classmate made a year long project of building a vacuum balloon.
He had more success than I gather the physics teacher thought he would have, but
still no-go for positive buoyancy.

I was sort of thinking of doing it for a package to mail via the
USPS. Watch them try to figure out the proper postage on something
which was a one or two foot sphere, but which didn't show up on their
scales. :-)

I was thinking of perhaps a titanium sphere, and wondering what
the minimum wall thickness to sustain it against a vacuum. But I never
got around to it.

What did he use for materials and shape?

Enjoy,
Don.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

Momentum?

-c.

"Roger Shoaf" wrote in message
...

"John Flanagan" wrote in message
...
On Mon, 21 Jul 2003 02:05:39 GMT, Jeff Wisnia
wrote:

So what *is* the pressure in a typical rubber party balloon. IIRC, it
gets
*lower* as the balloon expands. I think it's the same with soap
bubbles.

I suppose the pressure in one of those mylar party balloons must be
pretty
close to one atmosphere.

If the sides are not rigid it's always *exactly* atmospheric pressure.
If it expands either atmospheric pressure has dropped or the
temperature of the balloon has gone up.

Here's a question for everyone. Explain *exactly* the mechanics of
how and why a balloon floats :^)?

As I understand the physics, air is a fluid and the helium balloon being
lighter than the air around it floats just as a drop of oil will float if
released from the bottom of a volume of water.


Not as easy as one might think.

And a second one is why when you have a helium balloon in your car and
put the brakes on to stop, the balloon will float to the back of the
car instead of flying to the front like everything else. Again, what
are the mechanics that make it do so?

Again the air being heaver than the balloon the air has more mass. When
this mass is in motion, pressure is equal on all sides of the balloon.
When
the brakes are applied the air inside the car keeps moving at the speed
the
car was going until it hits the windshield. As air bunches up in the
front
part of the car, there is more air pressure at the front of the car and
less
at the back so the pressure in the front pushes the lighter balloon
backwards.

--
Roger Shoaf
If you are not part of the solution, you are not dissolved in the solvent.

(John Flanagan) writes:

The reason why a balloon floats in still air is because of the
pressure gradient between the top and the bottom of the balloon. Most
people don't think there is enough of a gradient to make a balloon
float but there is. They usually think of pressure drops between sea
level and the top of a mountain, not one over just a foot of height.
If the pressure was the same it would sink.

The only way that there would *not* be a pressure gradient across the
height of the balloon is if the material outside the balloon has zero
weight. This would happen only if there's no mass (i.e. a vacuum),
or if there's no apparent gravity (i.e. inside the orbiting space
station). If the material around the balloon does have weight, any
weight, then there must be a pressure gradient equal and opposite
to the weight - or the air wouldn't be at rest.

There's also a pressure gradient inside the balloon. Gravity is the
same inside and outside the balloon, but the density of helium is less
than air, so the pressure gradient is less inside than outside.

Dave

Subject: Helium lifting ability
From: jim rozen
Date: 22/07/03 19:56 GMT Daylight Time
Message-id:

In article ,
says...

The reason why a balloon floats in still air is because of the
pressure gradient between the top and the bottom of the balloon.

I really don't understand this. Are you talking about
the pressure gradient in the atmosphere?

Yes. Which by definition means that there is also a pressure gradient between
the top and bottom of the balloon, albeit a very minute one. The essential bit
though is only that there be a density gradient. The fact that this is caused
primarily by pressure is not relevant. It could also be caused by temperature.
The balloon rises to a point at which it displaces exactly its own mass. If it
were to rise higher it would displace less than its mass and so sink again. The
reverse would happen if it were to sink from the equilibrium point.


If that were the case then even a ballon filled with air
would float, because it sees the same gradient as one filled
with helium. But air-filled ballons don't float
because the amount of lift from that effect is very,
very tiny.

I'm not sure what you are taking the term "pressure gradient" to be but I think
you are misunderstanding it. It simply means there is a static density gradient
and the original point might have been better made using this term. There is no
way a balloon filled with air can float in air of the same density unless the
material of the balloon is also less dense than air.


Things float because the volume of fluid they displace,
weighs less than their own mass. This is true even in
incompressible fluids, like water for example.

Exactly. But in incompressible fluids objects generally either sink to the
bottom or float to the top. In compressible ones they can find an equilibrium
point from which they rise no higher. Strictly speaking even the tiny amount of
compressibility in liquids means that there is a small density gradient and a
possible equilibrium position for a submerged object but it's a very unstable
equilibrium and requires that the density of the object falls somewhere within
the tiny range of densities of the liquid between the top and bottom.


Dave Baker - Puma Race Engines (www.pumaracing.co.uk)
"How's life Norm?"
"Not for the squeamish, Coach" (Cheers, 1982)

In article , a
says...

I'm not sure what you are taking the term "pressure gradient" to be but I think
you are misunderstanding it. It simply means there is a static density gradient
and the original point might have been better made using this term. There is no
way a balloon filled with air can float in air of the same density unless the
material of the balloon is also less dense than air.

OK, replace pressure gradient with density gradient if you will.

But this is only apparent if the helium balloon is ballasted
so it is neither rising or sinking - if it is floating
free between the floor and ceiling. The effect is small,
much smaller than what makes the balloon provide lift in
the first place.

The density gradient effect can be seen with one of those
'cartesian diver' toys.

Jim

==================================================
please reply to:
JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com
==================================================

jim rozen wrote:

In article ,
says...

The reason why a balloon floats in still air is because of the
pressure gradient between the top and the bottom of the balloon.

I really don't understand this. Are you talking about
the pressure gradient in the atmosphere?

If that were the case then even a ballon filled with air
would float, because it sees the same gradient as one filled
with helium. But air-filled ballons don't float
because the amount of lift from that effect is very,
very tiny.

The pressure differential is only half of the equation. It has to be
balanced against the weight of the balloon. In the case of a
helium-filled balloon that rises, the net force resulting from the
pressure differential is greater than the weight of the balloon, so it
pushes the balloon up. For an air-filled balloon, the weight of the
balloon is greater than the resultant buoyant force, so the balloon
sinks.

The amount of force involved is not as tiny as you think. At sea level
at 59 deg F, the pressure gradient is about 0.000531 psi / ft, or
0.0765 psf / ft. To simplify calculations, let's assume we have a
balloon in the shape of a cube 1 ft on each side. The difference in
the upward pressure acting on the bottom square foot and the downward
pressure acting on the upper square foot is therefore 0.0765 lb, or
1.22 oz, acting in an upward direction. (Note that these numbers are
the same as the weight of one cubic foot of air under these conditions
-- this isn't a coincidence!) This force is greater than the combined
weight of a cubic foot of helium (at near ambient pressure) and a
balloon; it's less than the combined weight of a cubic foot of air and
a balloon. (An empty balloon this size would probably weigh 1/3 to 1/2
oz, based on the weight of a smaller balloon I had lying around.)

Things float because the volume of fluid they displace,
weighs less than their own mass. This is true even in
incompressible fluids, like water for example.

The weight of the fluid displaced is simply an easily computed
surrogate for the force due to the pressure differential. Both values
turn out to be exactly the same (regardless of whether the fluid is
compressible or not). But physically speaking, the balloon moves
because of the forces acting on it, and the force acting on it due to
the surrounding atmosphere is transmitted through pressure (which is
the result of individual gas molecules impinging on the balloon).

Bert

Very good description Bert.

John

On Tue, 22 Jul 2003 19:48:05 -0500, Bert wrote:

jim rozen wrote:

In article ,
says...

The reason why a balloon floats in still air is because of the
pressure gradient between the top and the bottom of the balloon.

I really don't understand this. Are you talking about
the pressure gradient in the atmosphere?

If that were the case then even a ballon filled with air
would float, because it sees the same gradient as one filled
with helium. But air-filled ballons don't float
because the amount of lift from that effect is very,
very tiny.

The pressure differential is only half of the equation. It has to be
balanced against the weight of the balloon. In the case of a
helium-filled balloon that rises, the net force resulting from the
pressure differential is greater than the weight of the balloon, so it
pushes the balloon up. For an air-filled balloon, the weight of the
balloon is greater than the resultant buoyant force, so the balloon
sinks.

The amount of force involved is not as tiny as you think. At sea level
at 59 deg F, the pressure gradient is about 0.000531 psi / ft, or
0.0765 psf / ft. To simplify calculations, let's assume we have a
balloon in the shape of a cube 1 ft on each side. The difference in
the upward pressure acting on the bottom square foot and the downward
pressure acting on the upper square foot is therefore 0.0765 lb, or
1.22 oz, acting in an upward direction. (Note that these numbers are
the same as the weight of one cubic foot of air under these conditions
-- this isn't a coincidence!) This force is greater than the combined
weight of a cubic foot of helium (at near ambient pressure) and a
balloon; it's less than the combined weight of a cubic foot of air and
a balloon. (An empty balloon this size would probably weigh 1/3 to 1/2
oz, based on the weight of a smaller balloon I had lying around.)

Things float because the volume of fluid they displace,
weighs less than their own mass. This is true even in
incompressible fluids, like water for example.

The weight of the fluid displaced is simply an easily computed
surrogate for the force due to the pressure differential. Both values
turn out to be exactly the same (regardless of whether the fluid is
compressible or not). But physically speaking, the balloon moves
because of the forces acting on it, and the force acting on it due to
the surrounding atmosphere is transmitted through pressure (which is
the result of individual gas molecules impinging on the balloon).

Bert


Please note that my return address is wrong due to the amount of junk email I get.
So please respond to this message through the newsgroup.

On Mon, 21 Jul 2003 02:05:39 GMT, Jeff Wisnia
wrote something
.......and in reply I say!:

So what *is* the pressure in a typical rubber party balloon. IIRC, it gets
*lower* as the balloon expands. I think it's the same with soap bubbles.

It will go past a maximum point, because as the balloon stretches, it
becomes weaker and therefore requires less PSI to expand, but inside
will always be higher than outside pressure.
************************************************** ****************************************
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Please remove ns from my header address to reply via email
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