Endless Blue – Week 61 – Weight in a Buoyant World   Leave a comment

Physics

Weight in a Buoyant World

Weight as we, beings that walk on legs, understand is meaningless underwater.  Shackled as we are to the surface of solid land, we experience the pull of gravity at a limited range along the bottom of the atmosphere.  To rise above this nadir takes vast amounts of effort, energy, and engineering from which the denizens of the Endless Blue are blissfully free.  Elquans essentially soar within their aquatic air in a manner that would leave us envious of their ease.

Officially (decided by some aloof Syntesthete scholars without consent of the general populace), weight is defined as the mass of an object multiplied by the pull of gravity on that object.  Unfortunately in an aquatic environment, as the surrounding water around an item increases in density, it begins to counteract the pull of gravity with the pull of buoyancy.  As a result, things as sea level weight more than those laying at the Continental Shelf.  What’s more, the composition of the water itself complicates this, as seawater with all its dissolved minerals (notably, such as salt) is denser than purified H2O.  Then the temperature of water is also a variant, as colder water (with its more closely compact atoms) being denser than warmer water (with its freely moving atoms).  This is even further compounded by the effect of gravity becoming stronger the closer a body is to it.  This means the pull of gravity is radically different at the bottom of the ocean that it would be at the opposite point at the tallest peak in the Vastness.

Because of this subjectiveness in measuring weight, the mass of an item is more important to know than its weight, and as such mass has become the defacto method of measuring the weight of an item.  Volume is a poor substitute due to manipulation by size (an item may be hollow inside, yet has a greater volume than a smaller solid sample) or arrangement (stacking cubes exactly takes up all the space, but using the same method with spheres leaves a lot of empty space between each unit).  Further, only the crudest estimations of volume can be achieved by measuring spacial dimensions like width, length, and depth (due in part to the War of Math), and the classical method of discovering volume — by immersion in a fluid-filled container and measuring the amount of displace liquid — is nearly impossible in an undersea environment.

Mass is determined in a three step process: by the use of a pair of balances and the utilization of weights.  Both balances work in the same manner — place the item being weighed on one half, and add the included weights to the other half until the level of both halves becomes equal, or horizontal.  One balance is inverted over the other, so that the positive and negative buoyancies are checked.  An item that is denser than the water it displaces will sink, and therefore register on the lower balance, while those items less dense will float upward and press against the upper balance.

The final part of the measurement quandary is solved with a depth gauge.  Depth gauges are simple to use yet difficult to construct.  They require a container free of water that is sealed over the opening with a layer of skin and sinew.  This sealed drum contraption measures the amount of pressure the surrounding water places on the elastic skin.  As depth increases, the added weight of the surrounding water also increases, putting pressure on the surface of anything that sinks lower.  As the pressure increases, the pressure pushes the skin down into the empty container deeper, and conversely as the pressure decreases by rising the skin retracts toward its level orientation.

This method of diametric weights and depth gauging works because the mass of the weights have already been determined, and mass does not change at different depths. The weights for these balances are specially made, so those for the upper balance are neutrally buoyant at sea level, while the weights for the lower balance are neutrally buoyant at lower depths (at which depth is dependent on the manufacture, with more expensive balance weights reaching neutral buoyancy at deeper depths).  Obviously, weights used at depths lower than the weights the bottom balance was designed with become useless, as the weights then have a higher buoyancy than the surrounding water, and will start floating upward.  The mitigating factor then becomes the point in which an item become neutrally buoyant.  At this point, it will press neither upward nor downward on either balance.  Solving this is very easily accomplished with only a minor adjustment of the depth at which the measuring is taking place.  The smallest of changes in depth triggers an item’s buoyancy — maintaining neutral buoyancy is like maintaining balance on a tightrope.  While the act of maintaining neutral buoyancy is nearly an instinctual reaction in living things, the manual manipulation of neutral buoyancy is a finicky skill that requires the finesse of a master.

Mass is measured in grams.  A gram is defined as the mass of a cubic amount of water at the temperature of melting ice.  The reason for the use of melting ice is two fold — first, to decide upon a level of temperature that is easily determined by observance of natural physics, and second for the non-altered purity of the medium.

What this all means in game terms is that encumbrance is a messy business to figure out.  With a myriad of items in a common knapsack, all having different density and thus different levels of neutral buoyancy, simulating weight in an exact manner is counterproductive.  Best to just take the general weight of all items at face value and keep using the weights listed in rulebooks.

Instead, think of encumbrance as drag.  The more gear and items strapped to the individual’s body, the more the dynamic sleekness of the piscean form is broken up, thus producing drag as the water needs to be pushed out of the way.   Buoyancy also contributes to drag.  When an object that is neutrally buoyant at sea level is brought down to the Shelf, the water around it is constantly pushing upward on it, trying to restore it to that neutral point.  The piscean carrying such an object needs to constantly work against this natural upward thrust, which lessens the effectiveness of their swimming movement.  The same mechanic works on a heavy item that would naturally sink to the bottom of the ocean — a piscean has to constantly counteract that drag downward, diverting the efficiency of moving forward.  Viewing weight as drag has the added benefit of taking into account instances of balanced ballast, where the mass of objects that sink matches that of objects that float, producing a neutral buoyancy.  These characters are still considered “encumbered” due to the change in their naturally sleek, aquadynamic shape.

However, sometimes the mass of an item is too much for a piscean’s strength to overcome.  Too much encumbrance and the individual cannot counteract the natural buoyancy.  Heavy chains and weights such as those used in many Elquan funeral traditions can drag a piscean to the bottom of the sea, and conversely too many hollow containers that are lighter than water will drag the helpless individual upward like a hot-air balloon.  Sometimes these normally undesirable situations can be turned to be useful, as in the aforementioned case of funerals, or escaping a predator quickly by jettisoning negatively buoyant gear and “shooting” up to the point of neutral buoyancy.

Counteracting positive or negative buoyancy is still an effective mitigator when it comes to beasts of burden.  The sleds that are used to carry supplies and resources take advantage of cancelling buoyancy with malleable containers that can be “inflated” or “bled” or of their lighter-than-water contents to achieve neutral buoyancy, but despite this the weight is still applied as drag on the pack animal when it moves.

“There is the weight of gold, the weight of worry, and the weight of sin.  In the Mistress’ eyes, they are all the same…”
— Dogma of the Church of Olyhydra

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