Quantities of Matter, and Specific Gravity
Donald G. Shead
Feb.24,1998ds
There are two things regarding the “quantity of matter” in any
mass,object or body of it that vary greatly:
One is its size, bulk or volume. The amount of space it takes up.
The other is its heaviness or weight. The force required by the
ground or other support to prevent it from further freefall. This force
varies in proportion to the acceleration due to gravity from which it is
prevented. i.e. the weight of a body varies depending on where it is
measured!
The product of a body’s measured weight and its volume, divided by the
acceleration due to gravity is a measure of its “density”. How much matter
is contained in that volume. The density of pure water at a temperature
just above its freezing point, and at standard atmospheric pressure (at
Earth’s sea level) is _quite_ constant: This fact can be readily determined
virtually anywhere on Earth’s surface. While other pure substances also
have constant densities that may be even more constant, the density of
water was chosen as a _standard_ for density because it is commonly
available , and it is more easily divided into measurable units than some
of the other substances that could serve the same purpose:
At Earth’s surface, and for most practical purposes, the measured
weight (heaviness) of a cubic foot of water is about 62.428 pounds. The
product of this weight and its volume (1 cubic foot), divided by the
acceleration due to gravity (32.175 ft/sec^2) is 1.94 “slug”: Where a slug
is the unit of mass in the US Engineering (foot-pound-second) system of
weights and measures; and has units (_plural_) of 32.175#/(32.175'/sec^2) =
1 pound sec^2/foot!
“Specific gravity” is the ratio of the heaviness (weight) of a
substance compared to the heaviness of an _equal volume_ of water! So it
is that the specific gravity of water is: 62.428 lbs/cf, divided by 62.428
lbs/cf ; is equal to ONE! All of the units cancel. The specific gravity
of water is one!
The weight of a cubic foot of ‘rolled steel’ is (found to be) about
490 pounds: Its specific gravity is: 490#/cf divided by 62.428#/cf; is
equal to 7.85; which is an ‘accepted value’ for that substance.
This means that rolled steel is 7.85 times heavier than an equal volume of
(pure) water. A substance with a specific gravity less than one (1) will
float on water; a substance with a specific gravity greater than one will
sink
So that individual engineers, and or other scientists don’t have to
determine these values each time they need them, TABLES showing the weights
per cubic foot of various common substances, and their specific gravities
are commonly available in engineering, and other specialized texts.
Donald Shead <u10...@snet.net>
To see my web page, please CLICK *there*>http://pages.cthome.net/donsr/
What a tangled web we weaved; prematurely conceived what was first
perceived :-)
Donald G. Shead
The weight of a cubic foot of (pure) water is about 62.428 pounds: Its
specific gravity is: 62.428#/cf divided by 62.428#/cf is equal to one (1).
A substance with a specific gravity less than one (1) will float on water;
Donald Shead <u10...@snet.net>
To see my web page, please CLICK *there*>http://pages.cthome.net/donsr/
What a tangled web we weaved; prematurely conceived what was first
perceived.
Donald G. Shead
Does anyone know the history of how the cubic centimeter of water
became the unit of mass in the metric (cgs) system of weights and measures?
Donald Shead <u10...@snet.net>
To see my web page, please CLICK *there*>http://pages.cthome.net/donsr/
What a tangled web we weaved; prematurely conceived what was first
perceived :-)
Donald G. Shead
Feb. 23,1998ds:
Density is the amount of material substance in an object per unit
volume. Volume is the amount of space an object occupies:
At Earth's surface, and for most practical purposes, the measured
weight of a cubic foot of pure water is about 62.428 pounds. The product
of
this weight and its volume (1 cubic foot), divided by the acceleration due
to gravity (32.175 ft/sec^2) is 1.94 "slugs": Where a slug is the unit of
mass in the US Engineering (foot-pound-second) system of weights and
measures; and has units (_plural_) of 32.175#/(32.175'/sec^2) = 1 pound
sec^2/foot!
At Earth's surface, and for most practical purposes, the measured
weight of a cubic decimeter of pure water is about 9.81 newtons (2.204
pounds). The product of this weight and its volume (1 cubic decimeter),
divided by the acceleration due to gravity (9.81 m/sec^2) is 1 "kilogram":
Where a kilogram is the unit of mass in the metric (meter-kilogram-second)
system of weights and measures; and has units (_plural_) of 9.81 N/(9.81
m/sec^2) = 1 N sec^2/m!
At Earth's surface, and for most practical purposes, the measured
weight of a cubic centimeter of pure water is about 981 dynes. The product
of this weight and its volume (1 cc), divided by the acceleration due
to gravity (981 centimeters/sec^2) is 1 "gram": Where a gram is the unit
of
mass in the metric (centimeter-gram-second) system of weights and
measures; and has units (_plural_) of 981 dynes/(981 c/sec^2) = 1 dyne
sec^2/c!
Does this make any sense to anyone but me?
Donald G. Shead
A balance scale indicates the RATIO of a body's weight (w) to the
acceleration due to gravity (g): For any given mass of matter it will have
the same reading (for 'w/g') regardless of the value of 'g' _wherever_ it
is: In Death Valley, on Pikes Peak or on the moon!
Right?
Uncle Al
Donald G. Shead wrote:
>
> A balance scale indicates the RATIO of a body's weight (w) to the
> acceleration due to gravity (g): For any given mass of matter it will have
> the same reading (for 'w/g') regardless of the value of 'g' _wherever_ it
> is: In Death Valley, on Pikes Peak or on the moon!
>
> Right?
A balance scale accurately compares masses if the acceleration field is
uniform (flat; zero gradient, divergence, curl) across the apparatus.
Mass is invariant. You need to be a little careful if your "gravity" is
created by spinning a small-radiused construct. On an astronomical
body, local field inhomogeneities (gravity, centripetal acceleration)
are generally too small to consider on a stationary (relative) sub-meter
scale.
--
Uncle Al Schwartz
Uncl...@ix.netcom.com ("zero" before @)
http://pw2.netcom.com/~uncleal0/uncleal.htm
http://www.ultra.net.au/~wisby/uncleal.htm
http://www.guyy.demon.co.uk/uncleal/uncleal.htm
(Toxic URLs! Unsafe for children, Democrats, and most mammals)
"Quis custodiet ipsos custodes?" The Net!
Donald G. Shead
Uncle Al <Uncl...@ix.netcom.com> wrote in article
<34F44C...@ix.netcom.com>...
snip
>
> A balance scale accurately compares masses if the acceleration field is
> uniform (flat; zero gradient, divergence, curl) across the apparatus.
> Mass is invariant. You need to be a little careful if your "gravity" is
> created by spinning a small-radiused construct. On an astronomical
> body, local field inhomogeneities (gravity, centripetal acceleration)
> are generally too small to consider on a stationary (relative) sub-meter
> scale.
So what you're saying then, is that any balance scale accurately compares
[the weight of] masses [objects or body's of matter] if the acceleration
field is uniform....
Any mass, object or body of matter contains an invariant quantity of matter
as long as it remains intact!
Jim Carr
"Donald G. Shead" <u10...@snet.net> writes:
>
> A balance scale indicates the RATIO of a body's weight (w) to the
>acceleration due to gravity (g): For any given mass of matter it will have
>the same reading (for 'w/g') regardless of the value of 'g' _wherever_ it
>is: In Death Valley, on Pikes Peak or on the moon!
>
>Right?
Almost. It _compares_ those ratios for two objects.
It relies on the acceleration field being suitably uniform. Thus
it also works just fine in space if you provide a uniform acceleration
to it, and badly near a black hole, where the field is not uniform.
--
James A. Carr <j...@scri.fsu.edu> | Commercial e-mail is _NOT_
http://www.scri.fsu.edu/~jac/ | desired to this or any address
Supercomputer Computations Res. Inst. | that resolves to my account
Florida State, Tallahassee FL 32306 | for any reason at any time.
Donald G. Shead
SPECIFIC GRAVITY is the heaviness of a substance compared to that of [an
equal volume of] water, and it is expressed without units. i.e. The units
CANCEL. In the metric system specific gravity is the same as in the
English system. If something is 7.85 times as heavy as an equal volume of
water (such as iron is) its specific gravity is 7.85. Its density is 7.85
grams per cubic centimeter, or 7.85 kilograms per liter, or 7.85 metric
tons per cubic meter. [OR 7.85 SLUGS PER CUBIC FOOT: WHERE THE SPECIFIC
GRAVITY EQUALS 490#/C.F./(65.428#/C.F. OF WATER), EQUALS 15.23
SLUGS/CF/(1.94 SLUGS PER CUBIC FOOT OF WATER)
Donald G. Shead
The US engineering unit of weight (or any other force - such as that of a
stretched spring, or a bat striking a ball, or a locomotive pulling a
train) is called the POUND. One pound is defined as the amount of force
required to cause one slug of matter to accelerate one foot per second
every second. A pound is roughly equal to four newtons. A kilogram of
matter at Earth's surface has a weight of about 9.80 newtons. A slug of
matter at Earth’s surface would have a weight of 32.175 pounds.
Donald G. Shead
Well Jim,
I wasn't planning on anyone's using a balance scale near a black hole.
It would be dangerous I'd think.
Donald G. Shead
Mar.1/98ds
The amount of matter, and/or inertia, in _any_ mass (object or body)
of matter, is equal to its weight divided by the (local) acceleration due
to gravity (g). Thus for the kilogram, at Sevres, it is w/g = 9.81 N/(9.81
m/sec^2) = 1 N sec^2/m = One kilogram! That is the kilogram _has_ units;
that do _not_ cancel!
The density, inertia and/or amount of matter (m) in _any particular
volume_ of matter is equal to the weight of that volume divided by the
_local_ acceleration due to gravity; per (divided by) the volume: m =
(w/g)/(vol). Thus for one cubic foot of water its density is 62.5#/(32.175
ft/sec^2) per 1 cubic foot = (1.94# sec^2/ft) per cubic foot = 1.94
slug/cubic foot! Where a slug (also) has units that don’t cancel: One slug
= 1# sec^2/ft!
SPECIFIC GRAVITY is the heaviness of a substance compared to that of
In the metric system specific gravity is the same as in the English
system. If something is 7.85 times as heavy as an equal volume of water
w_platinum_/w_water_ = 21.5.]
Right?
brian whatcott
On 1 Mar 1998 15:22:26 GMT, Donald G. Shead,u10...@snet.net says...
>
> SPECIFIC GRAVITY is the heaviness of a substance compared
> to that of
>an equal volume of water, and it is expressed without units: _they cancel_!
> In the metric system specific gravity is the same as in the English
>system. If something is 7.85 times as heavy as an equal volume of water
>(such as iron is) its specific gravity is 7.85. [w_iron_/w_water_ = 7.85:
>w_platinum_/w_water_ = 21.5.]
>
> Right?
>
> Donald Shead <u10...@snet.net>
Right? Well, you expected a few nit-picks, so I'll
go ahead.
The term "Specific" as used in scientific terms is meant to have a very
specific (sorry!) meaning: namely, the value of some characteristic value
per unit mass.
So one might naively expect "Specific Gravity" to refer to some
characteristic associated with gravity (like volume, weight etc) per unit mass.
And of course, that would be a wrong assumption ( rather like "Specific
Thrust" is similarly variant) so the currently preferred term is "Relative Density"
which serves exactly the definition you had in mind.
Regards
Whatcott Altus OK
Ken Fischer
brian whatcott (in...@intellisys.net) wrote:
: On 1 Mar 1998 15:22:26 GMT, Donald G. Shead,u10...@snet.net says...
: > SPECIFIC GRAVITY is the heaviness of a substance compared
: > to that of an equal volume of water, and it is expressed
: >without units: _they cancel_!
:
: So one might naively expect "Specific Gravity" to refer to some
: Density" which serves exactly the definition you had in mind.
Does that also apply to the electrolyte in
my car battery? :-) Or ocean water?
Ken Fischer
---
brian whatcott
On Thu, 5 Mar 1998 00:50:34 GMT, Ken Fischer,kefi...@iglou.com
says...
>
>brian whatcott (in...@intellisys.net) wrote:
>: On 1 Mar 1998 15:22:26 GMT, Donald G. Shead,u10...@snet.net
says...
>: > SPECIFIC GRAVITY is the heaviness of a substance compared
>: > to that of an equal volume of water, and it is expressed
>: >without units: _they cancel_!
>[snip]
>:
>: So one might naively expect "Specific Gravity" to refer to some
>: And of course, that would be a wrong assumption ( rather like "Specific
>: Thrust" is similarly variant) so the currently preferred term is "Relative
>: Density" which serves exactly the definition you had in mind.
>: Whatcott Altus OK
>
> Does that also apply to the electrolyte in
>my car battery? :-) Or ocean water?
>
>Ken Fischer
>---
Relative Density as applied to battery electrolytes or sea water,
meaning the ratio mass/volume : mass(w)/volume(w)
or in other words, the mass ratio compared with water for a
given volume - is universally applicable.
But if you are talking about ordinary usage - we are stuck
with S.G. for a long time yet, I suspect!
Whatcott Altus OK
Donald G. Shead
brian whatcott <in...@intellisys.net> wrote in article
<6dlm1n$8...@enews3.newsguy.com>...
snip<
............ the currently preferred term is "Relative
> >: Whatcott Altus OK
Thanks Brian! I didn't know that. It makes sense!
snip<
............... the mass ratio compared with water for a
> given volume - is universally applicable.
>
> But if you are talking about ordinary usage - we are stuck
> with S.G. for a long time yet, I suspect!
>
> Whatcott Altus OK
I don't really think we _need_ to be stuck with S.G.; I for one will
encourage using the term "Relative Density" for the ratio of the_weight_ of
a substance compared with the weight of an equal volume of water: Where
Relative Density is the ratio of how much heavier, OR _lighter_, the
substance is than an equal volume of (pure) water: 490#/ft^3 of
steel/62.5#/ft^3 of water = 7.85. I think it makes more sense!
Thanks again, Brian