Microgravity parable

From Herb Schaltegger:
The statement you are quoting has been accepted physics since it was
spelled out in detail in Isaac's Principia.

You and Newton on a first name basis these days?

At his mixers, he may have preferred to be called "Sir Isaac" to impress the ladies.


~ CT

Herb Schaltegger wrote:

(Stuf4) wrote:
The statement you are quoting has been accepted physics since it was
spelled out in detail in Isaac's Principia.

You and Newton on a first name basis these days?


Come on, give the guy a break. What he stated is a fact. Gravity is a FORCE.
Acceleration is the result of a force being applied to a mass. Assasinating a
character even when he says something that makes sense devalues the newsgroup.
It is, as far as I know, still in the "sci" hiearchy and not in the "psy".
Analyse the facts, not the personality.


Experiments on the station should really be relabled as "free floating"
instead of "0 g" or microgravity.

"Microgravity" should be for experiments that happen *really* far from the
earth where the gravitational force is truly "micro". As I recall, gravity at
the altitude of the space station is still fairly powerful.

The fact that gravity is still pulling objects down in the space station may
not matter for current experiments where free fall is sufficient. But later
on, when they start to study gravity seriously, it will matter.

In article ,
h (Rand Simberg) wrote:

On 8 Oct 2003 10:19:49 -0700, in a place far, far away,
(Stuf4) made the phosphor on my
monitor glow in such a way as to indicate that:


- Gravity is *distinctly different* from acceleration.

While gravity has a property of acceleration, it is *not*
acceleration.

Your continued repetition of this statement does not make it true.

No.

The fact that it's true is what makes it true.

Gravity is *not* acceleration.

Gravity is a *force* that sometimes *causes* accelerations.

--
Alan Baker
Vancouver, British Columbia
"If you raise the ceiling 4 feet, move the fireplace from that wall
to that wall, you'll still only get the full stereophonic effect
if you sit in the bottom of that cupboard."

On Thu, 09 Oct 2003 05:18:22 GMT, in a place far, far away, Alan Baker
made the phosphor on my monitor glow in such a
way as to indicate that:

In article ,
h (Rand Simberg) wrote:

On 8 Oct 2003 10:19:49 -0700, in a place far, far away,
(Stuf4) made the phosphor on my
monitor glow in such a way as to indicate that:


- Gravity is *distinctly different* from acceleration.

While gravity has a property of acceleration, it is *not*
acceleration.

Your continued repetition of this statement does not make it true.

No.

The fact that it's true is what makes it true.

No, gravity doesn't "have a property of acceleration." The statement
is not true.

--
simberg.interglobal.org * 310 372-7963 (CA) 307 739-1296 (Jackson Hole)
interglobal space lines * 307 733-1715 (Fax) http://www.interglobal.org

"Extraordinary launch vehicles require extraordinary markets..."
Swap the first . and @ and throw out the ".trash" to email me.
Here's my email address for autospammers:

In article ,
(Stuf4) wrote:

And when astronauts came back from space, they would be crystal clear
that while they floated around, with their bodies having no relative
acceleration in relation to their spacecraft, gravity never came
anywhere close to zero at any point in their trip. They *never*
experienced zero gravity. They experienced zero acceleration.

Traveling at constant speed in a straight line, were they?

,------------------------------------------------------------------.
| Joseph J. Strout Check out the Mac Web Directory: |
| http://www.macwebdir.com |
`------------------------------------------------------------------'

From Joe Strout:
(Stuf4) wrote:

And when astronauts came back from space, they would be crystal clear
that while they floated around, with their bodies having no relative
acceleration in relation to their spacecraft, gravity never came
anywhere close to zero at any point in their trip. They *never*
experienced zero gravity. They experienced zero acceleration.

Traveling at constant speed in a straight line, were they?

Thanks for the correction! I meant to say...

They experienced zero acceleration *relative to their spacecraft*.

(Or micro accel, to be more exact.)


~ CT

(Stuf4) wrote in message
From Joe Strout:
(Stuf4) wrote:

And when astronauts came back from space, they would be crystal clear
that while they floated around, with their bodies having no relative
acceleration in relation to their spacecraft, gravity never came
anywhere close to zero at any point in their trip. They *never*
experienced zero gravity. They experienced zero acceleration.

Traveling at constant speed in a straight line, were they?

Umm, Joe, in rereading what I originally wrote (as quoted) you can see
that it was explicitly stated:

"...their bodies having no relative acceleration in relation to their
spacecraft..."


~ CT



Thanks for the correction! I meant to say...

They experienced zero acceleration *relative to their spacecraft*.

(Or micro accel, to be more exact.)


~ CT

In sci.space.policy, on Wed, 08 Oct 2003 13:51:30 -0500, Joe Strout
sez:

` In article ,
` (Stuf4) wrote:

` And when astronauts came back from space, they would be crystal clear
` that while they floated around, with their bodies having no relative
` acceleration in relation to their spacecraft, gravity never came
` anywhere close to zero at any point in their trip. They *never*
` experienced zero gravity. They experienced zero acceleration.

` Traveling at constant speed in a straight line, were they?

Travelling in a straight line following a "geodesic" (what's a
geodesic called when you're not on geos?) of spacetime. -GR

--
================================================== ========================
Pete Vincent
Disclaimer: all I know I learned from reading Usenet.

In article ,
(Stuf4) wrote:

************************************************** ****************

Scientist: "I just measured this box with my ruler. It has one
human-foot."

CT: "You mean to say that the box is one foot long, right?"

Scientist: "I mean to say that it has one human-foot."

CT: "How can it have a human foot if it is just a box? I'm certain
that what you mean to say is that your box has the same length as one
human foot, with length being a common quality to both the box and the
foot. But a "human-foot" as a bodily appendage is distinctly
different from a "foot" as a measure of length."

Scientist: "You are just being pedantic. The terminology you are
using may apply to the field of biology, but it does not apply to my
specialty field of measuring boxes."

CT: "Um, no. I see a distinct conceptual difference between a human
foot and the length of the side of a box."

Scientist: "Now you're just playing with semantics!"


~

I hope this analogy helps to illuminate the fundamental problem with
the widely used terminology: zero/microgravity.

- Gravity is *distinctly different* from acceleration.

While gravity has a property of acceleration, it is *not*
acceleration. A 'g' is a unit of acceleration standardized upon a
particular case of acceleration due to gravity (the gravitational
acceleration at the surface of the Earth).

Likewise...

- A human foot is *distinctly different* from length.

A foot may have the property of length, but it is *not* length.

To confuse acceleration measured in 'g' with gravity is the same type
of error as confusing a length measured in 'feet' with those
appendages at the end of your legs.

*

As there are alternative standards for measuring length that have no
basis at all in the human foot (take the meter, for example) a
standard unit of acceleration could be defined on a scale that has
nothing to do with gravity.

Let's say that this time next year, the SI unit for acceleration gets
defined as 10 meters/second^2. This unit standard gets named in honor
of the man who helped popularize acceleration entertainment for
countless families across the planet. The SI standard unit of accel
will be known as the Disney, abbreviated as "D". The unit of 1-D is
based upon a certain ride in Florida that spins you around with 10
m/s^2 of lateral acceleration, nothing at all to do with gravity.

Those wishing to conform with this SI standard can use the following
conversion factor (rounded):

1 D = 1.019 g

Notice that if NASA were to adopt this hypothetical standard, "Zero-g"
research would then be called "Zero-D" research. And when people
thought of Disney's spinning ride in Florida, they would be crystal
clear that measures of acceleration need not be based upon gravity.
No need for confusion.

And when astronauts came back from space, they would be crystal clear
that while they floated around, with their bodies having no relative
acceleration in relation to their spacecraft, gravity never came
anywhere close to zero at any point in their trip. They *never*
experienced zero gravity. They experienced zero acceleration.

They didn't even experience that. They were accelerating; it's just that
everything around them was accelerating at the same rate.


.

I hope this helps to clear up the mess that was created by the terms
"zero/microgravity". And if those words ever get stitched to another
NASA mission patch, I hope it includes Mickey Mouse's face to remind
us all of the silliness behind the misusage of those terms.


~ CT

--
Alan Baker
Vancouver, British Columbia
"If you raise the ceiling 4 feet, move the fireplace from that wall
to that wall, you'll still only get the full stereophonic effect
if you sit in the bottom of that cupboard."

From Alan Baker:
snip
And when astronauts came back from space, they would be crystal clear
that while they floated around, with their bodies having no relative
acceleration in relation to their spacecraft, gravity never came
anywhere close to zero at any point in their trip. They *never*
experienced zero gravity. They experienced zero acceleration.

They didn't even experience that. They were accelerating; it's just that
everything around them was accelerating at the same rate.

I took Joe's rebuttal as a correction. But your rebuttal, Alan, is
helping me to see accuracy in the original statement...

The word -experience- carries subjectivity. What you experience
hinges upon your -frame of reference-. From the astronauts point of
view, the point of view of their non-inertial reference frame of the
spacecraft that is affected by gravitational acceleration, the
experience is zero relative acceleration.


So let's say, for the sake of argument here, that we are agreed that
it is accurate to say that they _experienced_ zero acceleration. An
obviously salient question follows...

Could we not, by the principle of equivalence (gravitational mass
being equivalent to inertial mass) therefore conclude that this
experience of zero relative acceleration be equivalent to a statement
that:

They experienced zero gravity?

The answer might be yes, except for one showstopper. Unlike
Einstein's famous "elevator" thought experiment, it is quite possible
to determine that the spacecraft is in the gravitational field of the
planet (and Sun and Moon, etc). The most simple way to do this is to
look out the window.

(Einstein's principle here was addressed on an earlier thread a few
days ago.)


~ CT