Criticism of the terms "Zero Gravity" and "Microgravity"

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Here is another analogy to help illuminate accurate physics as to why
zero-g is not "zero gravity":

Imagine floating down a river. You are moving at the same speed as
the water around you. It is accurate to say that there is zero
relative current. But it is totally inaccurate to say that you are
dry, in zero water.

Likewise, orbiting around the Earth can be thought of as flowing with
Earth's gravity in acceleration toward the center of the Earth. It is
accurate to say that there is zero-g, or zero acceleration relative to
your spacecraft. But it is *not* accurate to say that you are in zero
gravity.

The pull of gravity in orbit is strong. That's why you go around in
an orbit. Likewise the flow of a river can be very strong, even if
the water around you may look still while you're floating in it.

To play on that old commercial... Gravity? You're soaking in it!


~ CT

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Link -
http://tinyurl.com/CriticismOfTheTermZeroGravity
http://groups.google.com/group/sci.s...AEd0bc915ae768

On Apr 7, 2:07 pm, wrote:
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Here is another analogy to help illuminate accurate physics as to why
zero-g is not "zero gravity":

Imagine floating down a river. You are moving at the same speed as
the water around you. It is accurate to say that there is zero
relative current. But it is totally inaccurate to say that you are
dry, in zero water.

Likewise, orbiting around the Earth can be thought of as flowing with
Earth's gravity in acceleration toward the center of the Earth. It is
accurate to say that there is zero-g, or zero acceleration relative to
your spacecraft. But it is *not* accurate to say that you are in zero
gravity.

The pull of gravity in orbit is strong. That's why you go around in
an orbit. Likewise the flow of a river can be very strong, even if
the water around you may look still while you're floating in it.

To play on that old commercial... Gravity? You're soaking in it!


And to continue the analogy,

Standing on the Earth and feeling the pull of gravity is akin to
standing on the riverbed and feeling the flow of the current.

Are you deliberately being pedantic?If you understand gravity, then you are
the only person on this earth who does. Is there in fact anywhere where
there is zero gravity? Its merely a shorthand term for free fall with no
acceleration or deceleration. It reminds me of that old joke about the truck
which was overloaded with budgerigars until they all took off..

Brian

--
Brian Gaff -
Note:- In order to reduce spam, any email without 'Brian Gaff'
in the display name may be lost.
Blind user, so no pictures please!
wrote in message
...
A continuation of Message-ID:
.com
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Here is another analogy to help illuminate accurate physics as to why
zero-g is not "zero gravity":

Imagine floating down a river. You are moving at the same speed as
the water around you. It is accurate to say that there is zero
relative current. But it is totally inaccurate to say that you are
dry, in zero water.

Likewise, orbiting around the Earth can be thought of as flowing with
Earth's gravity in acceleration toward the center of the Earth. It is
accurate to say that there is zero-g, or zero acceleration relative to
your spacecraft. But it is *not* accurate to say that you are in zero
gravity.

The pull of gravity in orbit is strong. That's why you go around in
an orbit. Likewise the flow of a river can be very strong, even if
the water around you may look still while you're floating in it.

To play on that old commercial... Gravity? You're soaking in it!


~ CT

From Brian Gaff:
Are you deliberately being pedantic?If you understand gravity, then you are
the only person on this earth who does. Is there in fact anywhere where
there is zero gravity? Its merely a shorthand term for free fall with no
acceleration or deceleration. It reminds me of that old joke about the truck
which was overloaded with budgerigars until they all took off..

I am talking about the most basic understanding of what gravity is and
what it is not. A first cut that Newton as well as Einstein could
agree on. As simple as this:

TRUE OR FALSE - THERE IS NO GRAVITY IN SPACE.

Controversial? Pedantic? Have a look at what NASA astronauts
themselves have to say...


=========================
"According to Chang-Diaz, the sensation of weightlessness is much like
one might expect. "With no gravity, it's just like you're floating,"
he said. "You can fly like Peter Pan." "
(http://www.dailyprincetonian.com/2000/05/12/998/)

"And then, the last part is we'll go to space where there's no gravity
and see how our lungs work."
"The scientists will be looking at us in no gravity."
"You actually eliminate it because there is no gravity."
(http://spaceflight.nasa.gov/shuttle/.../sts-107/crew/
intbrown.html)

"The other neat thing is that since there is no gravity, if you're
sitting in the commander's seat, I can actually hover above you so
that we can make better use of space in space."
(http://www.nasa.gov/multimedia/podca...STS118webcast-
transcript_prt.htm)

"Out in space there is no gravity to speak of, and there are no walls
- so we really don’t have the feeling of up or down, forward and aft,
left and right at all."
-- Full quote in context:
"With the help of the divers we can float at a certain depth in the
water and practice our tasks. However, gravity is still there so we
still have a sense of up and down. Plus the pool walls give you the
sense of right, left, forward and aft in your periphery vision. Out in
space there is no gravity to speak of, and there are no walls - so we
really don’t have the feeling of up or down, forward and aft, left and
right at all."
-- Also this:
"It is amazing how microgravity creeps in. There really are no rest
days up here because the lack of gravity is always there, eating away
at your fitness level, bone mass and muscle mass."
(http://www.nasa.gov/mission_pages/st.../expedition15/
journal_sunita_williams_11_prt.htm)

"SCOTT: Hi. I'm Scott. I'm from New Jersey. I was wondering, how do
astronauts sleep in space because there's no gravity."
-- The astronaut who answered this question at length provided no
correction.
(http://www.nasa.gov/multimedia/podcasting/
115_robinson_transcript.html)
=========================


And in case your conclusion is that this view of gravity in space is
particular to human spaceflight, this one is out of JPL:


=========================
Since there's no gravity in space, Lemur could work upside down, as
long as one limb is anchored.
(http://www.nasa.gov/vision/universe/roboticexplorers/
lemur-20060511.html)
=========================


There are many, many more quotes like this out there. Certain
official NASA websites that attempt to explain "microgravity" are
particularly egregious. They speak of "zero gravity" and
"microgravity" with no demonstrated understanding of the most
fundamental distinction between gravitational acceleration versus
other types of acceleration. How ironic to see this coming from an
administration that continually stresses how it promotes education in
science. What NASA is promoting here is BAD science. This topic has
been discussed at length in years past. Here are links to two old
threads:

http://groups.google.com/group/sci.s...3c8a2847cbd0d7
http://groups.google.com/group/sci.s...7c82364fcd6be5


~ CT

Brian Gaff wrote:
Are you deliberately being pedantic?If you understand gravity, then you are
the only person on this earth who does. Is there in fact anywhere where
there is zero gravity?


From a practical point of view, free falling or being at a LaGrange
point cancels out the obvious aspects of gravity. But it doesn't
generate 0 gravity environment.

Consider this possibly flawed analogy:

You are sunbathing outdoors in middle of winter. The cold temperature
may cancel out the heat from the sun, making the sun appear to be
neutral for temperature, but the sun's UV rays are still impacting your
skin.

Until we fully understand gravity, we must consider the possibility that
acceleration of mass may not be the only impact gravity has on objects.

From John Doe :
Brian Gaff wrote:
Are you deliberately being pedantic?If you understand gravity, then you are
the only person on this earth who does. Is there in fact anywhere where
there is zero gravity?

From a practical point of view, free falling or being at a LaGrange
point cancels out the obvious aspects of gravity. But it doesn't
generate 0 gravity environment.

Lagrange points are *not* points where gravity is cancelled out. (One
obvious check it the equilateral L4/L5 points, where the gravity
vectors are at 60 degrees to each other, forming the equilateral
triangle.) In the three-body situation, there is only one point where
gravitational forces are in balance. It is a point between the two
primary bodies, and is *not* even the same as the L1 Lagrange point.
The reason why they're different is because to keep the two primaries
at a distance, they need to be rotating around each other (leading to
Coriolis and centrifugal effects in the rotating Lagrange reference
frame).

Consider this possibly flawed analogy:

You are sunbathing outdoors in middle of winter. The cold temperature
may cancel out the heat from the sun, making the sun appear to be
neutral for temperature, but the sun's UV rays are still impacting your
skin.

NASA's misrepresentation of thermal science is another matter! I was
watching a Discovery Channel series over the weekend and *cringed*
when I heard a shuttle commander compare the aero-heating temperature
that the shuttle experiences on deorbit as being "as hot as the Sun".
TOTALLY failing to grasp the conceptual distinction between
temperature and heat. (This too has been discussed at length in past
years here on sci.space)

Until we fully understand gravity, we must consider the possibility that
acceleration of mass may not be the only impact gravity has on objects.

Again, the original criticism addresses the failure to grasp the most
basic effects of gravity that have been thoroughly explained since the
1680's. It is the "what" of gravity that has been confused, let alone
the "how".

And if we ever do unravel the "how", then we can hope for technologies
like anti-gravity. But it is important to learn how to walk before
attempting to run.


~ CT