Buoyancy is Imaginary
 

Several months ago, I made this statement during a discussion of
stability here. The minor flame war that resulted made it impractical
to defend the proposition and it wasn't much fun anyway.

While I was away, I had occasion to put together a web site section on
the subject of stability and made the subject line the title of the
first chapter. If anyone is interested in the technical aspects of
what floats their boat with a minimum of math, click:

http://www.rogerlongboats.com/Stability.htm

My son's former physics teacher reviewed the buoyancy section and
pronounced it "Beautifully explained" so it's had some minimum of
vetting aside from being basically a written version of a guest
lecture I used to present to college students.

The last chapter is a brief introduction to the endless foolishness in
the Coast Guard stability regulations for sailboats. This recently
got me an email from a retired inspector saying basically, "Thank
goodness someone finally said something!"

Enjoy

Buoyancy is Imaginary
 

Never argue bouyancy with Roger Long. ;-)

--
KLC Lewis

WISCONSIN
Where It's So Cool Outside, Nobody Stays Indoors Napping
www.KLCLewisStudios.com

"Roger Long" wrote in message
...
Several months ago, I made this statement during a discussion of
stability here. The minor flame war that resulted made it impractical
to defend the proposition and it wasn't much fun anyway.

While I was away, I had occasion to put together a web site section on
the subject of stability and made the subject line the title of the
first chapter. If anyone is interested in the technical aspects of
what floats their boat with a minimum of math, click:

http://www.rogerlongboats.com/Stability.htm

My son's former physics teacher reviewed the buoyancy section and
pronounced it "Beautifully explained" so it's had some minimum of
vetting aside from being basically a written version of a guest
lecture I used to present to college students.

The last chapter is a brief introduction to the endless foolishness in
the Coast Guard stability regulations for sailboats. This recently
got me an email from a retired inspector saying basically, "Thank
goodness someone finally said something!"

Enjoy

Buoyancy is Imaginary
 

Roger Long wrote:
Several months ago, I made this statement during a discussion of
stability here. The minor flame war that resulted made it impractical
to defend the proposition and it wasn't much fun anyway.

While I was away, I had occasion to put together a web site section on
the subject of stability and made the subject line the title of the
first chapter. If anyone is interested in the technical aspects of
what floats their boat with a minimum of math, click:

http://www.rogerlongboats.com/Stability.htm

My son's former physics teacher reviewed the buoyancy section and
pronounced it "Beautifully explained" so it's had some minimum of
vetting aside from being basically a written version of a guest
lecture I used to present to college students.

The last chapter is a brief introduction to the endless foolishness in
the Coast Guard stability regulations for sailboats. This recently
got me an email from a retired inspector saying basically, "Thank
goodness someone finally said something!"

Enjoy



A quote from last week that seems to apply here...

"The need to control has exceeded the need to make sense".


Good work, Roger.


Richard

Buoyancy is Imaginary
 

On Mon, 28 Sep 2009 09:14:57 -0700 (PDT), Roger Long
wrote:

Several months ago, I made this statement during a discussion of
stability here. The minor flame war that resulted made it impractical
to defend the proposition and it wasn't much fun anyway.

Buoyancy may be imaginary but experience has demonstrated that it's
better to be on a boat with it than without.

Buoyancy is Imaginary
 

"Roger Long" wrote in message
...
Several months ago, I made this statement during a discussion of
stability here. The minor flame war that resulted made it impractical
to defend the proposition and it wasn't much fun anyway.

While I was away, I had occasion to put together a web site section on
the subject of stability and made the subject line the title of the
first chapter. If anyone is interested in the technical aspects of
what floats their boat with a minimum of math, click:

http://www.rogerlongboats.com/Stability.htm

My son's former physics teacher reviewed the buoyancy section and
pronounced it "Beautifully explained" so it's had some minimum of
vetting aside from being basically a written version of a guest
lecture I used to present to college students.

The last chapter is a brief introduction to the endless foolishness in
the Coast Guard stability regulations for sailboats. This recently
got me an email from a retired inspector saying basically, "Thank
goodness someone finally said something!"

Enjoy




Way too simplistic, I'm afraid. You seem to attribute buoyancy to gravity
alone. WRONG!

Let's create a system that has 1/100 Earth gravity. Let's place a 1/100
Earth gravity sphere half full of water and half full of air in outer space.
Let's pressurize this sphere to one atmosphere. Let's float a boat in the
water. The boat that weighs a ton only weighs 1/100 ton in this sphere but
the atmospheric pressure is Earth normal. Therefore the pressure upwards on
the boat's hull would be the same as on earth (due to atmospheric pressure)
according to your ill-conceived theory. The boat that is already floating
100 times higher than on earth due to its being 1/100 the weight (mass)
would be pushed even higher. If your theory were correct this would not be
the case.

I rest my case.

Wilbur Hubbard

Buoyancy is Imaginary
 

KLC Lewis wrote:
Never argue bouyancy with Roger Long. ;-)

Why? I think Roger is making a big deal of a very fine distinction.
Its true that an object that is said to be "buoyant" does not generate a
force by itself, the force really comes from water pressure which in
turn is caused by gravity. But, the force is real and buoyancy is
simply a convenient way to aggregate the net pressure on an object. If
there were no force (regardless of what we call it) holding up a ship,
it would sink.

There are, of course, imaginary forces, such as Coriolis which appears
in non-inertial reference frames, but that is a different thing.

Buoyancy is Imaginary
 

On Mon, 28 Sep 2009 17:40:21 -0400, Jeff wrote:

KLC Lewis wrote:
Never argue bouyancy with Roger Long. ;-)

Why? I think Roger is making a big deal of a very fine distinction.
Its true that an object that is said to be "buoyant" does not generate a
force by itself, the force really comes from water pressure which in
turn is caused by gravity. But, the force is real and buoyancy is
simply a convenient way to aggregate the net pressure on an object. If
there were no force (regardless of what we call it) holding up a ship,
it would sink.

There are, of course, imaginary forces, such as Coriolis which appears
in non-inertial reference frames, but that is a different thing.

There are many words in the English language that aren't proper
scientific explanations of a phenomena. Try "beautiful" or "ugly" for
two examples.

Is the fact that there is no scientific justification for the term
"beautiful" reason to stop using it?

Cheers,

Bruce
(bruceinbangkokatgmaildotcom)

Buoyancy is Imaginary
 

On Sep 28, 7:55*pm, Bruce In Bangkok
wrote:
On Mon, 28 Sep 2009 17:40:21 -0400, Jeff wrote:
KLC Lewis wrote:
Never argue bouyancy with Roger Long. ;-)

Why? *I think Roger is making a big deal of a very fine distinction.
Its true that an object that is said to be "buoyant" does not generate a
force by itself, the force really comes from water pressure which in
turn is caused by gravity. *But, the force is real and buoyancy is
simply a convenient way to aggregate the net pressure on an object. *If
there were no force (regardless of what we call it) holding up a ship,
it would sink.

There are, of course, imaginary forces, such as Coriolis which appears
in non-inertial reference frames, but that is a different thing.

There are many words in the English language that aren't proper
scientific explanations of a phenomena. Try "beautiful" or "ugly" for
two examples.

Is the fact that there is no scientific justification for the term
"beautiful" *reason to stop using it?

Cheers,

Bruce
(bruceinbangkokatgmaildotcom)

Roger has the same mistaken impression that many people have, that it
takes energy to hold an object up against gravity. NO, it takes no
energy for a rigid body to hold an object up against gravity. If his
son thinks it takes energy for a table to hold a book up, he needs to
re-learn physics. If you hold a book out with your arm extended, you
ARE using energy because your arm is not a rigid body and you are
exerting energy to keep the muscles tensed. This is equivalent to
holding something up with a leaky pneumatic cylinder. This is
completely different from buoyant forces holding a boat up which takes
NO energy. A buoyant situation that would require energy would be an
object flating within a container at a constant level where the
container has a leak. In that case energy IS required to keep the
object at a constant level because you have to pump in liquid to
replace that that leaks out.
His observation that buoyancy is the result of unbalanced pressure is
trivial in some cases and not entirely accurate in others. A
floating boat has pressure from below balancing the weight from above
and the net buoyant force is simply equal to the weight of water
displaced. A balloon floating in air (or water) has no unbalanced
pressure and the buoyant force is simply equal to the weight of the
medium displaced. A buoyant force is not imaginary simply due to
being a "net force". Forces are vector quantities and the total force
acting on a body is the vector sum of all forces.

Buoyancy is Imaginary
 

There is no such thing as a rigid support.

The book on the table actually does compress the table an amount equal to it's mass.

Buoyancy is Imaginary
 

On Sep 28, 10:00*pm, cavelamb wrote:
There is no such thing as a rigid support.

The book on the table actually does compress the table an amount equal to it's mass.

The book does compress the table slightly but once compressed, no
moire energy is required to hold up the book.

Although I am adamant about buoyancy not requiring energy input, I
think Roger may be nearly right about buoyancy being the result of
unbalanced pressures even for a balloon floating in air. I think it
is related to transfer of momentum of air or water molecules to said
balloon being diff tween top and bottom although after a rum n coke it
aint too obvious to me.
However, consider our balloon as a ping pong ball immersed in a vat of
small lead shot. The lead shot are our water molecules. Shake said
vat to produce thermal motion and said ping pong ball rises to the top
magically.

I never did like the semantics of "imaginary forces" because even for
such so-called "imaginary forces", they can lead to work being done.
Thus the distinction is almost entirely semantics (yeah yeah, I know
frames of reference and all).

Buoyancy is Imaginary
 

On Sep 28, 10:00*pm, cavelamb wrote:
There is no such thing as a rigid support.

The book on the table actually does compress the table an amount equal to it's mass.

BTW Cavelamb, are you a caver?

Buoyancy is Imaginary
 

Frogwatch wrote:
On Sep 28, 10:00 pm, cavelamb wrote:
There is no such thing as a rigid support.

The book on the table actually does compress the table an amount equal to it's mass.

Compression is an expression of stored energy. :)

BTW Cavelamb, are you a caver?

I've been lost in the dark once or twice.
But not for a while now.

Buoyancy is Imaginary
 

Jeff wrote:
KLC Lewis wrote:
Never argue bouyancy with Roger Long. ;-)

Why? I think Roger is making a big deal of a very fine distinction. Its
true that an object that is said to be "buoyant" does not generate a
force by itself, the force really comes from water pressure which in
turn is caused by gravity. But, the force is real and buoyancy is
simply a convenient way to aggregate the net pressure on an object. If
there were no force (regardless of what we call it) holding up a ship,
it would sink.

There are, of course, imaginary forces, such as Coriolis which appears
in non-inertial reference frames, but that is a different thing.

Budding naval architects should teach themselves the rudiments of
dimensional analysis... and then they won't make appalling cockups in
their use of incompatible units.

Buoyancy is Imaginary
 

On Sep 29, 2:14*am, Roger Long wrote:

I'd be glad if you'd remove the apostrophe from "in all it's varying
amounts " on your Buoyancy.htm.

Cheers

Bil

Buoyancy is Imaginary
 

Goofball_star_dot_etal wrote:
Jeff wrote:
KLC Lewis wrote:
Never argue bouyancy with Roger Long. ;-)

Why? I think Roger is making a big deal of a very fine distinction.
Its true that an object that is said to be "buoyant" does not generate
a force by itself, the force really comes from water pressure which in
turn is caused by gravity. But, the force is real and buoyancy is
simply a convenient way to aggregate the net pressure on an object.
If there were no force (regardless of what we call it) holding up a
ship, it would sink.

There are, of course, imaginary forces, such as Coriolis which appears
in non-inertial reference frames, but that is a different thing.

Budding naval architects should teach themselves the rudiments of
dimensional analysis... and then they won't make appalling cockups in
their use of incompatible units.
So who do you think is making an appalling cockup? And in which context?

Buoyancy is Imaginary
 

Jeff wrote:
Goofball_star_dot_etal wrote:
Jeff wrote:
KLC Lewis wrote:
Never argue bouyancy with Roger Long. ;-)

Why? I think Roger is making a big deal of a very fine distinction.
Its true that an object that is said to be "buoyant" does not
generate a force by itself, the force really comes from water
pressure which in turn is caused by gravity. But, the force is real
and buoyancy is simply a convenient way to aggregate the net pressure
on an object. If there were no force (regardless of what we call it)
holding up a ship, it would sink.

There are, of course, imaginary forces, such as Coriolis which
appears in non-inertial reference frames, but that is a different thing.

Budding naval architects should teach themselves the rudiments of
dimensional analysis... and then they won't make appalling cockups in
their use of incompatible units.
So who do you think is making an appalling cockup? And in which context?

There are numerous examples of equating inconsistant units. Here is one
example of gobeldygook:

"Note the net downwards displacement of the air. The essence of all
Newtonian physics is the symmetry of energy conservation (the equal and
opposite reaction business). The work done by accelerating the mass of
air downwards is exactly equal to the work required to keep the aircraft
aloft. The work required to shift it from left to right in the
animations is an important aspect of the drag that the engine must
overcome."

http://www.rogerlongboats.com/Circulation.htm

Buoyancy is Imaginary
 

On Sep 29, 7:32*am, Goofball_star_dot_etal
wrote:

There are numerous examples of equating inconsistant units. Here is one
example of gobeldygook:

The reaction to these presentations on the web is always the same.
The professionals, especially teachers, like them and they gather all
sorts of nit picks from others. That particular bit of gobeldygook
came from an article published in a leading aviation Emagazine and,
last I heard, was being used as an introduction to the subject in at
least one college course.

These are not intended to be physics texts. There are plenty of
those. The intent is to provide a plain language viceral
understanding of the basic principles. Units and terms most
recognizable to the reader with little prior knowledge are preferable
in a quick and light treatment.

Why this kind of thing worthwhile? I've had a whole career (I'm
hardly "budding") to watch people with naval architectural degrees and
complete understanding of the math and unit consistency come to
really bone headed conclusions that have greatly hampered the
commercial and educational sail industries because they didn't start
with a gut understanding of the physics and let numbers and anal
attention to unit consistency lead them to absurd conclusions. If
they had first understood the subject on this kind of level, they
might have made better use of the mathematical tools. Most college
courses and texts start right off with the math.

These articles are just starting points and not intended to be much
above the level of Sunday newpaper supplement stuff. Professionals
tend to see them for what they are and their limited value and net
posters as opportunities to show how smart they are. Happy to have
provided the opportunity.

--
Roger Long

Buoyancy is Imaginary
 

On Sep 29, 10:02*am, Roger Long wrote:
On Sep 29, 7:32*am, Goofball_star_dot_etal
wrote:

There are numerous examples of equating inconsistant units. Here is one
example of gobeldygook:

The reaction to these presentations on the web is always the same.
The professionals, especially teachers, like them and they gather all
sorts of nit picks from others. *That particular bit of gobeldygook
came from an article published in a leading aviation Emagazine and,
last I heard, was being used as an introduction to the subject in at
least one college course.

These are not intended to be physics texts. *There are plenty of
those. *The intent is to provide a plain language viceral
understanding of the basic principles. *Units and terms most
recognizable to the reader with little prior knowledge are preferable
in a quick and light treatment.

Why this kind of thing worthwhile? *I've had a whole career (I'm
hardly "budding") to watch people with naval architectural degrees and
complete understanding of the math and unit consistency *come to
really bone headed conclusions that have greatly hampered the
commercial and educational sail industries because they didn't start
with a gut understanding of the physics and let numbers and anal
attention to unit consistency lead them to absurd conclusions. *If
they had first understood the subject on this kind of level, they
might have made better use of the mathematical tools. *Most college
courses and texts start right off with the math.

These articles are just starting points and not intended to be much
above the level of Sunday newpaper supplement stuff. *Professionals
tend to see them for what they are and their limited value and net
posters as opportunities to show how smart they are. *Happy to have
provided the opportunity.

--
Roger Long

Roger:

Generally pretty good if you take out the part about requiring energy
to float. I'll re-read it sometime today.

Frogwatch (former college Physics teacher who has forgotten more'n he
ever learned)

Buoyancy is Imaginary
 

Frogwatch wrote:

These articles are just starting points and not intended to be much
above the level of Sunday newpaper supplement stuff. Professionals
tend to see them for what they are and their limited value and net
posters as opportunities to show how smart they are. Happy to have
provided the opportunity.

--
Roger Long

Roger:

Generally pretty good if you take out the part about requiring energy
to float. I'll re-read it sometime today.

Frogwatch (former college Physics teacher who has forgotten more'n he
ever learned)


Can we at least agree that the floating boat actually does raise the water level?

Buoyancy is Imaginary
 

On Sep 29, 10:13*am, Frogwatch wrote:

Generally pretty good if you take out the part about requiring energy
to float. *I'll re-read it sometime today.


That's not really what it was meant to convey but it's a work in
progress. I'll keep this in mind when I get around to the next round
of revisions.

--
Roger Long

Buoyancy is Imaginary
 

"cavelamb" wrote in message
m...

Can we at least agree that the floating boat actually does raise the water
level?

Absolutely. To the same extent that lighting a match increases global
warming. ;-)
--
KLC Lewis

WISCONSIN
Where It's So Cool Outside, Nobody Stays Indoors Napping
www.KLCLewisStudios.com

Buoyancy is Imaginary
 

KLC Lewis wrote:
"cavelamb" wrote in message
m...
Can we at least agree that the floating boat actually does raise the water
level?

Absolutely. To the same extent that lighting a match increases global
warming. ;-)


Actually, KC, it took considerably more energy to MAKE that match
than it gives off.

Entropy is still increasing.

Buoyancy is Imaginary
 

On Tue, 29 Sep 2009 07:02:36 -0700 (PDT), Roger Long
wrote:

On Sep 29, 7:32*am, Goofball_star_dot_etal
wrote:

There are numerous examples of equating inconsistant units. Here is one
example of gobeldygook:

The reaction to these presentations on the web is always the same.
The professionals, especially teachers, like them and they gather all
sorts of nit picks from others. That particular bit of gobeldygook
came from an article published in a leading aviation Emagazine and,
last I heard, was being used as an introduction to the subject in at
least one college course.

These are not intended to be physics texts. There are plenty of
those. The intent is to provide a plain language viceral
understanding of the basic principles. Units and terms most
recognizable to the reader with little prior knowledge are preferable
in a quick and light treatment.

Why this kind of thing worthwhile? I've had a whole career (I'm
hardly "budding") to watch people with naval architectural degrees and
complete understanding of the math and unit consistency come to
really bone headed conclusions that have greatly hampered the
commercial and educational sail industries because they didn't start
with a gut understanding of the physics and let numbers and anal
attention to unit consistency lead them to absurd conclusions. If
they had first understood the subject on this kind of level, they
might have made better use of the mathematical tools. Most college
courses and texts start right off with the math.

These articles are just starting points and not intended to be much
above the level of Sunday newpaper supplement stuff. Professionals
tend to see them for what they are and their limited value and net
posters as opportunities to show how smart they are. Happy to have
provided the opportunity.


Roger, you appear to be re-inventing the wheel. Here is the definition
of buoyancy taken from the Webster dictionary - note the edition date:

2. (Physics) The upward pressure exerted upon a floating body
by a fluid, which is equal to the weight of the body;
hence, also, the weight of a floating body, as measured by
the volume of fluid displaced.
[1913 Webster]

Cheers,

Bruce
(bruceinbangkokatgmaildotcom)

Buoyancy is Imaginary
 

On the capsize issue, it seems to me that this should be addressed the same way
that the FAA did for load limits (G factors).

Differentiate by heeling moments - ie sail area and wind strength.

Rather than trying to say that a particular layout is "safe", determine the
allowable wind strength for different sail arrangements.

Top sails, sky sails and lighter kites for lighter conditions and strip down
for higher (Or Rated) winds.

Buoyancy is Imaginary
 

On Sep 29, 8:12*pm, Bruce In Bangkok
wrote:

Roger, you appear to be re-inventing the wheel.

I sure hope I am. There isn't supposed to be anything new here.
We're talking about physics after all. It's just supposed to be an
entertaining discussion that makes the subject a bit more accessible
than a physics textbook and emphasizes points that I have encountered
a lot of confusion about, even among people who have advanced
degrees. Read through to the last section. The situation with
sailing vessels arose because USCG naval architects understood all the
math (and how to keep their units consistent:) but never held in their
mind a gut level understanding of what the number actually represented
and who boats act in the real world.

--
Roger Long

Buoyancy is Imaginary
 

On Sep 29, 11:04*pm, cavelamb wrote:
On the capsize issue, it seems to me that this should be addressed the same way
that the FAA did for load limits (G factors).

Differentiate by heeling moments - ie sail area and wind strength.

Rather than trying to say that a particular layout is "safe", determine the
allowable wind strength for different sail arrangements.

Top sails, sky sails and lighter kites for lighter conditions and strip down
for higher (Or Rated) winds.

That actually doesn't work. The real issue, which has never been
addressed properly by regulation, is unexpected wind increases and the
rate of vessel response. Having the proper sail set for a specific
wind velocity isn't going to make you safe if there is a squall
bearing down that you are not prepared for. Current USCG regulations
for sailing passenger vessels will let you have a vessel that can be
capsized by that squall by reducing the sail plan to an unusably small
area for normal conditions. At the same time, the will prevent the
certification, in many cases, of a vessel that would be knocked down
by the squall but recover without flooding. It's crazy. Be sure to
read the last section of the stability site.

Sail area is only one of several factors effecting heeling moment.
Siimple course changes that create luffing cause dramatic reductions
in heeling moment as any sailor knows. So does easing sheets and
reefing.

Every properly operated sailboat on the wind will have its sailplan
and trim adjusted to bring it to a normal heel angle. There is then
some larger angle at which bad things can happen such as water
entering open hatches or capsizing in the case of the wide flat
vessels the USCG rules favor. It is the margin between those two
angles, and its relationship to the possible speed of response to
sudden wind increases that is the critical factor. This is
independent of the total sail area. Sailing at 10 degree heel with a
large sail plan in a 15 knot wind that suddenly doubles in strength is
very much the same as sailing at the same angle with a sail reduced by
reefing or striking individual sails in a 30 knot wind that suddenly
doubles in strength. Proper regulation might require sail reductions
at some specifice heel angle as SOP and would insure sufficient margin
between this angle and the angle of downflooding or capsizing. This
is independent of the maximum total sail that might be carried. It's
a matter of hull design, not sail plan. USCG rules let you operate,
and indeed even promote the operation, of dangerous hulls with total
sail area restrictions that are irrelevant to actual safety in the
winds where accidents are most likely to occur.

All of this is very statistical and you can only get a handle on what
is required by population analysis of a large number of vessels that
draws a line between the ones that have capsized and those that have
not. One of the few intelligent things the Coast Guard did in the
history of sail regulation was recognize this fact and attempt such an
analysis. Unfortunately, they couldn't find data on any capsizes so
they just threw a lot of absurd dynamic theory at the problem and came
up with a mess that plagues large sailing vessel regulation to this
day. I conducted a much larger population study in the early 1980's
for the USCG and ASTA joint task force on sailing school vessel
regulations. We had data on vessels that had capsized by that time so
we were able to justify some improvements in the regulation of
educational vessels but it was no help to the commercial fleet that
still operates under the original crazy criteria. We still had to
work within the existing USCG methods though so sailing school vessels
still have the flawed emphasis on total sail area.

I took all the data I had at hand as a result of this project and
performed another population analysis that evaluated only hull
characteristics and put no restrictions on total sail that could be
carried or even measured sail plan at all. This created the same,
actually better, distinction between successful vessels and casualties
than the application of the USCG methods. A draft of this paper sent
to a friend and fellow researcher in England led to many of the
principles being incorporated in their much more rational set of
regulations for large sailing vessels. I got too busy though trying
to make a living, keep my business going, and start being a father to
ever finish up the paper for publication.

--
Roger Long

Buoyancy is Imaginary
 

Roger Long wrote:
On Sep 29, 11:04 pm, cavelamb wrote:
On the capsize issue, it seems to me that this should be addressed the same way
that the FAA did for load limits (G factors).

Differentiate by heeling moments - ie sail area and wind strength.

Rather than trying to say that a particular layout is "safe", determine the
allowable wind strength for different sail arrangements.

Top sails, sky sails and lighter kites for lighter conditions and strip down
for higher (Or Rated) winds.

That actually doesn't work. The real issue, which has never been
addressed properly by regulation, is unexpected wind increases and the
rate of vessel response. Having the proper sail set for a specific
wind velocity isn't going to make you safe if there is a squall
bearing down that you are not prepared for. Current USCG regulations
for sailing passenger vessels will let you have a vessel that can be
capsized by that squall by reducing the sail plan to an unusably small
area for normal conditions. At the same time, the will prevent the
certification, in many cases, of a vessel that would be knocked down
by the squall but recover without flooding. It's crazy. Be sure to
read the last section of the stability site.


I think I get your point now.

FAR 25, which covers load factors and gust loading in commercial aircraft
doesn't have to deal with flooding and the resultant stability changes!

Buoyancy is Imaginary
 

Roger Long wrote:
On Sep 29, 7:32 am, Goofball_star_dot_etal
wrote:

There are numerous examples of equating inconsistant units. Here is one
example of gobeldygook:

The reaction to these presentations on the web is always the same.
The professionals, especially teachers, like them and they gather all
sorts of nit picks from others. That particular bit of gobeldygook
came from an article published in a leading aviation Emagazine and,
last I heard, was being used as an introduction to the subject in at
least one college course.

These are not intended to be physics texts. There are plenty of
those. The intent is to provide a plain language viceral
understanding of the basic principles. Units and terms most
recognizable to the reader with little prior knowledge are preferable
in a quick and light treatment.

Why this kind of thing worthwhile? I've had a whole career (I'm
hardly "budding") to watch people with naval architectural degrees and
complete understanding of the math and unit consistency come to
really bone headed conclusions that have greatly hampered the
commercial and educational sail industries because they didn't start
with a gut understanding of the physics and let numbers and anal
attention to unit consistency lead them to absurd conclusions. If
they had first understood the subject on this kind of level, they
might have made better use of the mathematical tools. Most college
courses and texts start right off with the math.

These articles are just starting points and not intended to be much
above the level of Sunday newpaper supplement stuff. Professionals
tend to see them for what they are and their limited value and net
posters as opportunities to show how smart they are. Happy to have
provided the opportunity.

--
Roger Long

The point is not that I am a "clever clogs" but that you publish stuff
as an "expert" and get it plain wrong. As it happens I am just "an oily
rag".

The vertcal force on an airfoil (lift) is equal to vertcal *rate of
increase of momentum* of the surrounding air. Not displacement, work or
anything else.

Force has the dimensions (MLT-2) the same as Mass (M) times acceleration
(L-2) (from F=ma)or the same as mass flow rate (MT-1) times velocity
(LT-1). M represents Mass, L length and T time. 1/T^2 is represented as
T-2 etc.

In the case of airfoils, turbines etc. there is not a fixed mass but a
mass flow. It is a lot easier to measure the pressures over an airfoil
than the increasing momentum of the air but they are two sides of the
same coin.

No work is done on a plane in level fight at constant speed. Its
potential energy is not increasing with height and its kinetic energy is
not increasing with velocity. The lift is equal to its weight and its
drag is equal to the thrust. All the power ends up heating the air,
although initially some goes into increasing the kinetic energy of the
air you cannot get at this number by looking at the lift, as you
suggest, since kinetic energy and momentum are not the same thing.

Context re-inserted:

"Note the net downwards displacement of the air. The essence of all
Newtonian physics is the symmetry of energy conservation (the equal and
opposite reaction business). The work done by accelerating the mass of
air downwards is exactly equal to the work required to keep the aircraft
aloft. The work required to shift it from left to right in the
animations is an important aspect of the drag that the engine must
overcome."

http://www.rogerlongboats.com/Circulation.htm

Work is not Imaginary (was Buoyancy is Imaginary)
 

Goofball_star_dot_etal wrote:

/snip/
No work is done on a plane in level fight at constant speed. Its
potential energy is not increasing with height and its kinetic energy is
not increasing with velocity. The lift is equal to its weight and its
drag is equal to the thrust. All the power ends up heating the air,
although initially some goes into increasing the kinetic energy of the
air you cannot get at this number by looking at the lift, as you
suggest, since kinetic energy and momentum are not the same thing.


Hmmmm. a mostly reasonable review - but the idea that force times
distance is not equal to work is somewhat radical, don't you think?

And if the force (usually called thrust in this context,)which was
provided to oppose the drag on the plane due to its airspeed, is
multiplied with the airspeed rather than some air distance - the work
becomes the power expended in opposing drag.

But you knew that, I'm sure - you were just trying to provide a gut feel
for the physics, huh? :-)

Brian W

Work is not Imaginary (was Buoyancy is Imaginary)
 

brian whatcott wrote:
Goofball_star_dot_etal wrote:

/snip/
No work is done on a plane in level fight at constant speed. Its
potential energy is not increasing with height and its kinetic energy
is not increasing with velocity. The lift is equal to its weight and
its drag is equal to the thrust. All the power ends up heating the
air, although initially some goes into increasing the kinetic energy
of the air you cannot get at this number by looking at the lift, as
you suggest, since kinetic energy and momentum are not the same thing.


Hmmmm. a mostly reasonable review - but the idea that force times
distance is not equal to work is somewhat radical, don't you think?


I said no work was done *on the (air)plane*. Since we only have the
airplane and the air, the work done by the thrust of the engine moving
the airplane through a distance all goes into the air as (kinetic)
energy or heat in its wake.

And if the force (usually called thrust in this context,)which was
provided to oppose the drag on the plane due to its airspeed, is
multiplied with the airspeed rather than some air distance - the work
becomes the power expended in opposing drag.

But you knew that, I'm sure

True.

- you were just trying to provide a gut feel
for the physics, huh? :-)

No I was responding to Roger's statement:

"The work done by accelerating the mass of air downwards is exactly
equal to the work required to keep the aircraft aloft"

I think he meant "force" but it is difficult to tell..

Buoyancy is Imaginary
 

On Oct 1, 11:36*am, Goofball_star_dot_etal
wrote:


The point is not that I am a "clever clogs" but that you publish stuff
as an "expert" and get it plain wrong. As it happens I am just "an oily
rag".

For the record: I have never claimed to be an expert on aerodynamics
and I'm not. I'm just a writer. I've also never claimed to have
"discovered" anything new about the subject as has often been
claimed. I wrote a couple of articles on the subject once that an
aviation magazine published and a professor of aerodynamics found
useful as an introduction to the subject.

I'll also agree BTW that the web page with the circulation animation
isn't very good. I'd forgotten it was there until you brought it up.
The text isn't from the article but something I threw together quickly
to present the animation (which is from wind tunnel photographs and
not my interpretation of any physics) when the question of flow around
sails came up here quite a while ago. The page isn't linked on my web
site and therefore not really "published". Some of your comments are
valid and I'm going to rewrite it if I ever decide to provide a direct
link to it.

--
Roger Long

Buoyancy is Imaginary
 

Roger Long wrote:
On Oct 1, 11:36 am, Goofball_star_dot_etal
wrote:

The point is not that I am a "clever clogs" but that you publish stuff
as an "expert" and get it plain wrong. As it happens I am just "an oily
rag".

For the record: I have never claimed to be an expert on aerodynamics
and I'm not. I'm just a writer. I've also never claimed to have
"discovered" anything new about the subject as has often been
claimed. I wrote a couple of articles on the subject once that an
aviation magazine published and a professor of aerodynamics found
useful as an introduction to the subject.

I'll also agree BTW that the web page with the circulation animation
isn't very good. I'd forgotten it was there until you brought it up.
The text isn't from the article but something I threw together quickly
to present the animation (which is from wind tunnel photographs and
not my interpretation of any physics) when the question of flow around
sails came up here quite a while ago. The page isn't linked on my web
site and therefore not really "published". Some of your comments are
valid and I'm going to rewrite it if I ever decide to provide a direct
link to it.

--
Roger Long


There is a lot to like about your animations and presentations. I
particulary like "Removancy". It is expressions like "energy forces"
that spoil it for me. It does not mean anything, outside perhaps a seance.

My home PC is bust so you will have peace over the weekend.

Work is not Imaginary (was Buoyancy is Imaginary)
 

Goofball_star_dot_etal wrote:
....
Hmmmm. a mostly reasonable review - but the idea that force times
distance is not equal to work is somewhat radical, don't you think?


I said no work was done *on the (air)plane*. Since we only have the
airplane and the air, the work done by the thrust of the engine moving
the airplane through a distance all goes into the air as (kinetic)
energy or heat in its wake.

If I push a sled over snow with force F for distance D
it's usually accounted that the work I did ON the sled is F X D

....but I won't beat the topic down....
:-)

Brian W

Work is not Imaginary (was Buoyancy is Imaginary)
 

On Oct 2, 8:02*pm, brian whatcott wrote:
Goofball_star_dot_etal wrote:

...

Hmmmm. a mostly reasonable review - but the idea that force times
distance *is not equal to work is somewhat radical, don't you think?

I said no work was done *on the (air)plane*. Since we only have the
airplane and the air, the work done by the thrust of the engine moving
the airplane through a distance all goes into the air as (kinetic)
energy or heat in its wake.

If I push a sled over snow with force F for distance D
it's usually accounted that the work I did ON the sled is F X D

...but I won't beat the topic down....
:-)

Brian W

In regard to sudden gusts, why not use a breakaway strap like some
rock climbers use whose stitches break at some load allowing the sail
to be let out all the way.
How many boats get knocked down anyway? I mean cruising boats, racers
intend to be on the edge. My own boat, a 28' S2, if a sudden gust
came up, I'd never be able to hold the tiller and she'd round up into
the wind before getting knocked down.

Work is not Imaginary (was Buoyancy is Imaginary)
 

On Fri, 2 Oct 2009 17:42:17 -0700 (PDT), Frogwatch
wrote:

How many boats get knocked down anyway? I mean cruising boats, racers
intend to be on the edge. My own boat, a 28' S2, if a sudden gust
came up, I'd never be able to hold the tiller and she'd round up into
the wind before getting knocked down.

There are limits to that. If you get knocked down hard enough and
fast enough, the boom will hit the water and prevent the mainsail from
being eased. That's where the fun starts, and some boats will tend
to stay on their beam ends once they get knocked flat with the mast in
the water.

Work is not Imaginary (was Buoyancy is Imaginary)
 

On Oct 2, 8:42*pm, Frogwatch wrote:

In regard to sudden gusts, why not use a breakaway strap like some
rock climbers use whose stitches break at some load allowing the sail
to be let out all the way.

That was a huge issue and we did a lot of analysis on it back during
the sailing school vessel research in the early 80's. The sail and
rig forces caused by wave motion and rolling often exceed the forces
that would cause knockdown although only for brief periods. If you
put "fuses" in the rig, you would have stuff breaking constantly.

--
Roger Long

Work is not Imaginary (was Buoyancy is Imaginary)
 

On Fri, 2 Oct 2009 17:42:17 -0700 (PDT), Frogwatch
wrote:

On Oct 2, 8:02*pm, brian whatcott wrote:
Goofball_star_dot_etal wrote:

...

Hmmmm. a mostly reasonable review - but the idea that force times
distance *is not equal to work is somewhat radical, don't you think?

I said no work was done *on the (air)plane*. Since we only have the
airplane and the air, the work done by the thrust of the engine moving
the airplane through a distance all goes into the air as (kinetic)
energy or heat in its wake.

If I push a sled over snow with force F for distance D
it's usually accounted that the work I did ON the sled is F X D

...but I won't beat the topic down....
:-)

Brian W

In regard to sudden gusts, why not use a breakaway strap like some
rock climbers use whose stitches break at some load allowing the sail
to be let out all the way.
How many boats get knocked down anyway? I mean cruising boats, racers
intend to be on the edge. My own boat, a 28' S2, if a sudden gust
came up, I'd never be able to hold the tiller and she'd round up into
the wind before getting knocked down.


Not really a problem to design a boat that won't be knocked down. Good
form or ballast stability and a small rig.

Of course, as soon as the bloke buys this no-knock-down marvel he will
get a cruising gennaker, a storm spinnaker and fit a topmast so he can
fly a topsail. Probably it is impossible to build a vessel that is
impossible to knock down if the owner is in any way adventurous.

After all they once built an airplane that wouldn't spin and wouldn't
stall. It wasn't immensely popular.

Even full rigged ships quite frequently could send down their topmasts
in bad weather.

Cheers,

Bruce
(bruceinbangkokatgmaildotcom)

Work is not Imaginary (was Buoyancy is Imaginary)
 

On Fri, 2 Oct 2009 17:42:17 -0700 (PDT), Frogwatch
wrote:

On Oct 2, 8:02*pm, brian whatcott wrote:
Goofball_star_dot_etal wrote:

...

Hmmmm. a mostly reasonable review - but the idea that force times
distance *is not equal to work is somewhat radical, don't you think?

I said no work was done *on the (air)plane*. Since we only have the
airplane and the air, the work done by the thrust of the engine moving
the airplane through a distance all goes into the air as (kinetic)
energy or heat in its wake.

If I push a sled over snow with force F for distance D
it's usually accounted that the work I did ON the sled is F X D

...but I won't beat the topic down....
:-)

Brian W

In regard to sudden gusts, why not use a breakaway strap like some
rock climbers use whose stitches break at some load allowing the sail
to be let out all the way.
How many boats get knocked down anyway? I mean cruising boats, racers
intend to be on the edge. My own boat, a 28' S2, if a sudden gust
came up, I'd never be able to hold the tiller and she'd round up into
the wind before getting knocked down.

Guess again!

Work is not Imaginary (was Buoyancy is Imaginary)
 

Roger Long wrote:
On Oct 2, 8:42 pm, Frogwatch wrote:

In regard to sudden gusts, why not use a breakaway strap like some
rock climbers use whose stitches break at some load allowing the sail
to be let out all the way.

That was a huge issue and we did a lot of analysis on it back during
the sailing school vessel research in the early 80's. The sail and
rig forces caused by wave motion and rolling often exceed the forces
that would cause knockdown although only for brief periods. If you
put "fuses" in the rig, you would have stuff breaking constantly.

Most of the Nonsuch's (unstayed catboats) were built with aluminum masts
that tapered near the top. The marketing folks made a big point of how
the tip would flex to leeward and spill wind in gusts. Indeed, it
worked well and was helpful since it was easy to overpower the large
mainsail in gusty weather. (I learned to reef before going out, since
it was a lot easier to shake out than take in a reef!)

At the end of the production run they shifted to fiberglass masts that
were stiffer. The marketing folks stressed how this gave better
pointing ability in strong wind.