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Lifting power of Soda Bottles
Metric to English lifting power
Gallons to lifting power
1 & 2 liter bottles


How much air does it take to float things?

    Most American bottles have their volume written on the label in milliliters (ml). The metric system was founded on a pure-water-base. ("Fresh" water is pretty close to "pure" water.) Each 1 ml = 1 cc = 1 gram of pure water. If a soda bottle says ď591 mlĒ it means it will support 591 grams minus the mass (weight) of the bottle, according to Archimedes Principle. Plastic bottles donít weigh much, so you should be able to hold up about 561 grams in fresh water. (It should float that much in a lake.)

    Salt water is a little heavier, so it should float: 604.75 grams = 1.333 pounds per soda bottle of that size.

    Seawater weighs 1.025 grams/milliliter or 1 gallon of air should lift 8.556 pounds in seawater = 3,880.9 grams = 3.88 kilograms.

    Clear as mud?

    Add up all the displacements of all your bottles in the water, minus the weight of the bottles, and thatís how much your bottles should float.

How to Convert:

    Pounds to Kilograms, pounds/2.2 = kilograms
    Kilograms to Pounds, kilograms x 2.2 = pounds

    Example: If a small soda bottle of air will displace 591 ml (ignoring the weight of the bottle) it will lift 591 grams. That equals, 0.591 kilograms (kilo stands for 1000,) times 2.2 equals, converts to, 1.3002 pounds.

    1 gallon of air displaces, and thus will lift (minus the weight of the container,) 8.333 pounds in fresh water.

    1 gallon of air should lift 8.556 pounds in seawater = 3,880.9 grams = 3.88 kilograms.

    So a 35 gallon hefty garbage sack of air, in theory, should lift 291.66 pounds. However, itís not good to stretch one, so only fill it about half full. So it could lift about 145 pounds. Whereas a 50 gallon Hefty Garbage Sack, filled about half full should lift about 214 pounds.     Itís hard to know how much your island will weigh, but if you know how much it sinks down into the water, you should be able to make a good guess. Thatís how they measure ships.

Thus:
    A 1 liter bottle of air will float about 1 kilogram or 2.2 pounds in fresh water; or 1.025 kilograms or 2.255 pounds in seawater.
    A 2 liter bottle of air will float about 2 kilograms or 4.4 pounds in fresh water; or 2.05 kilograms or 4.51 pounds in seawater.
    (Without subtracting the weight of the bottle.

Example:
    My 591 ml soda bottle weighs about 30 grams.
So, it should hold up about 560 grams or 1.2 pounds in fresh water, 1.23 pounds in seawater.
With amounts this small, you have to round, so it's "about."

Underwater:
    Underwater, air is compressible, so a soft flotation component, such as a Hefty Garbage Sack will be slightly smaller, but since youíre not filling it over half way, it may not matter. But if youíre going to use these bags for deeper water, such as salvage work, you have to allow for expansion of the air as it rises to the surface, otherwise it might burst.

    Ping-pong balls will float too, but I donít know their volume.

    As I run across helpful information Iíll add it to this website.

    Thanks for your interest. Contact Dr. Hait
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