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.

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)

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.

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.

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).

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?

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.

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.

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?

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