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<p>[QUOTE=&quot;cwtokenman, post: 42705, member: 2100&quot;]I always understood gravity to be determined by only two things - mass and distance, such as in the following definition of gravity:</p><p><br /></p><p>&quot;All matters attract all other matter with a force proportional to the product of their masses and inversely proportional to the square of the distance between them.” </p><p><br /></p><p>I believe that physical size, and presence or not of a vacuum have no effect upon gravitational forces, but I would be interested in reading about those theories if you can provide a link. Acceleration due to gravitational forces may be greatly affected by the presence of vs. lack of a vacuum, but the gravitational force itself is unchanged.</p><p><br /></p><p>I also believe that most people, at least in the U.S., think in units of weight (pounds), and not in units of mass (slugs). An object&#039;s mass is a constant, but it&#039;s weight will vary in proportion to changes in the acceleration of gravity for any specific locale.</p><p><br /></p><p>When considering an ounce (volume) of water, the temperature should also be given, as the density of water varies, in an unproportional fashion, with changes in temperature. The liquid water is most dense at 3.97 deg. Centrigrade, when it has a specific gravity of 1.0000. But, for a more commonly encountered temperature, 1 fluid ounce of water at 62 degrees (sp. gr. of 0.9832) will weigh 437.5 grains and have a volume of 1.732 cubic inches. The numbers will change if considering an Imperial ounce.</p><p><br /></p><p>A few interesting (at least to me) water facts: </p><p><br /></p><p>Water is the only substance on Earth that exists in all three physical states of matter: solid, liquid and gas.</p><p><br /></p><p>Water is the only substance where the maximum density does not occur when solidified. As ice is lighter than water, it floats.</p><p><br /></p><p>(Ring) Science class is over now, you may now return to your regularly scheduled numismatic thread.[/QUOTE]</p><p><br /></p>

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