I’m trying to figure out how much weight a pool noodle or a Perrier bottle displaces in water, but admittedly I know very little of the math or science involved, except some story about Archimedes of Syracuse in a bathtub.
I figure the plastic bottle is easy enough: it’s just the weight of the air inside the bottle, calculated by the volume, right? With the pool noodle, though, it seems less apparent how to figure out how much of my fat ass I can displace.
Any help you can give me with my makeshift raft project is greatly appreciated. Thanks!
If you are making a raft you have to displace 1 pint of water per pound of your fat ass to reach neutral buoyancy. So your raft should have a volume of several pints per pound of your weight. If its inflatable, assume the air weighs nothing and add the weight of the raft material. If it’s made out of something solid, you need to know the density, or weight per pound of the material.
I’m not sure I understand your question. If your wondering how much weight each of those objects can support via their bouyancy, its a number of grams equal to their volume in cubic centimeters.
(Well, I guess if you want to be exact, it would also have to support the weight of the bottle itself, so you’d have to subtract that weight from the total amount it could support).
So, similarly for a cylindrical pool noodle, I find my pi r squared formula from my middle school notes (or google), and whatever the volume of the noodle is the amount of chubb it offsets?
Your pool noodle is almost weightless compared to water and displacing almost nothing in a pool by itself. Use Chronos’ suggestion and add weight to the noodle until it is submerged. That will tell you how many pool noodles you will need to to displace your own weight (if that’s what chubb means). Or use Simplicio’s suggestion and find your weight in grams (1 pound= 453.59237 grams), and you will need that many cc’s of volume in an an inflatable raft to offset your weight. Or use my suggestion and determine your weight in pounds and you will need that many pints of volume (1 pint = 28.875 cu. in.). That will only be enough volume to reach neutral buoyancy, and doesn’t count the weight of the material, so for a raft you need more than that. Twice as much might be a minimum safety factor.
If you make a raft, make sure to send us video of your maiden voyage.
True, but the effect will be small if the weights are made of a dense material. I never said it was the most accurate method, just that it was the simplest.
I’m using metric, since all my bottles have milliliters and I only know pints from beer. I figure to take into account my weight plus sundries, i’m going to say AT LEAST 150 liters being offset. 200 is probably better. That’s 400 Perrier bottles, but my mum goes through a 24 pack a week, so i’ll be getting a few from here alone!
Will bump this thread when I devise a test for pool noodles!
ETA: I’m assuming here you’re trying to just make yourself float while partly submerged. if you’re actually trying to build a raft or boat so you’ll be fully out of the water, then ignore everything below.
You now have a good procedure to determine the buoyancy provided by an air-filled liter bottle or a pool noodle. But you don’t have a procedure to figure out how much buoyancy you need.
You’ve been skipping the fact that *you *aren’t zero bouyancy. You float, at least partially. As such, if you weight 100Kg, you do *not *need 100Kg of additional pouyancy to float in water, since you’re already partially floating on your own.
If you’re obese enough, you may float just fine with no additional buoyancy at all. Why? Because human fat is less dense than water. OTOH, if you’re very lean, you may need 25 or 50 Kg of buoyancy to support yourself.
To find your own net weight in water you could take an ordinary bathroom spring-scale & put it at the bottom of a pool & stand on it while fully submerged. Do that both with a full deep breath and having fully exhaled. You’ll see that lung inflation makes a big difference.
Whatever weight you measure underwater, that’s how much you need to offset with your pool noodle or Perrier bottles.
