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<p>[QUOTE=&quot;John Burgess, post: 4889313, member: 105098&quot;]Density/Buoyancy. PVC it is heavier than freshwater, so are non-pvc plastics, except if we were to add in displacement or surface area of the item in question. You can float concrete in the ocean, if it&#039;s large enough and has enough displacement.</p><p><br /></p><p>the addition of the 2 tablespoons of salt to that 8 oz. of water ratio has it to where the less dense no-pvc containing plastics float, while the PVC doesn&#039;t. the variations in PVC density readings can be because the sample is flexible pvc vs. rigid, but flexible is ranged at (1.3-1.7g/cm3) depending on the mix now a days of the plastic.</p><p>in the old days though it was a lot of PVC in the mix. so in very many instances your samples density is going to be on the maximum side of the range, not the minimum.&nbsp; PET plastics are 1.3-1.4 density range.</p><p><br /></p><p>The salinity of 2 tablespoons of salt in 8 oz of water is roughly 4x the salinity of seawater. for seawater&#039;s salinity and density it&#039;s more like a half tablespoon per a pint.</p><p><br /></p><p>the water gets heavier with the addition of the dissolved salt and then one sinks, and the other floats.&nbsp; A gallon of saltwater weighs roughly 1/10th of a pound more than a gallon of freshwater because of the dissolved salt.</p><p><br /></p><p>Anyways, in a lot of cases this works, The PVC is denser than the water and stays down, the non-pvc plastic material is lighter than the water density, so it&#039;s bouyant.</p><p><br /></p><p>in fresh water nether would float as both are more dense than the density of the fresh water (0.99 at room temperature approx.)</p><p><br /></p><p>used to be an old experiment to float an egg in a glass of water, dump in a bunch of salt. do it slowly also until it becomes neutrally buoyant, top with freshwater to drop it, top with saltwater to raise it, fool your friends that it&#039;s magic!</p><p><br /></p><p>I did say &quot;kind of&quot; scientific. it&#039;s not all science really but it works. </p><p><br /></p><p>And hey, I&#039;m a bit of a nerd about stuff with my free time, 40 years ago and now. Why waste my time mixing stump remover and sugar when I can just go buy a model rocket engine at the store? ......Because its interesting to me.[/QUOTE]</p><p><br /></p>

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