Physics Rant: The Truth to Buoyancy in Diving

[bottomfeeder22]

So in accounting we have contra accounts, so might the answer be contra-bouyancy, balanced bouyancy, and inflated bouyancy?

Oooooh, Contra! ↑ ↑ ↓ ↓ ← → ← → B A start!

 

[b1gcountry]

Best game EVER!

 

[Zman96]

Ah, yes, Bluto's third law: Two men shall never occupy neighboring chairs, or urinals, excepting when sufficiently intoxicated, or attending a baseball game.

Tom

Even worse is going in the troughs at Wrigley Field, need to be really intoxicated then.

 

[Ken abucs]

Fenway used to have troughs too. We got upgraded to real urinals a couple of years ago.

Maybe that's what you need to get to the World Series.

 

[Dan Weidert]

You are forgetting distance, which also affects gravitational force. Whatever is above you in the atmosphere no longer contributes its mass to the equation, but your distance from the center point is now reduced, so whatever mass is still "beneath you" will produce a greater force. If most of the mass is still beneath you, and not above you, you get heavier. If the object is a consistent density, then you become lighter.

Look it up, it's interesting.

But yes, everyone agrees that at the Earth's center of gravity, the Earth produces no gravitational pull.

Tom

Tom,
You might want to rethink that statement. All matter in the universe (whether molecules of air above us, the rings of Saturn, or a distant star) exert a gravitational pull on all the other matter in the universe. Most of the time the gravitational pull is so small we can not detect it.

If you want a simple example of "whatever is above you" contributing to gravity you need look no further than the tides.

Weight is a function of gravity. Mass is not. I have the same mass on the earth as I do on the moon. However, I would weigh much less on the moon.

 

[Flightlead]

Tom,
You might want to rethink that statement. All matter in the universe (whether molecules of air above us, the rings of Saturn, or a distant star) exert a gravitational pull on all the other matter in the universe. Most of the time the gravitational pull is so small we can not detect it.

If you want a simple example of "whatever is above you" contributing to gravity you need look no further than the tides.

Weight is a function of gravity. Mass is not. I have the same mass on the earth as I do on the moon. However, I would weigh much less on the moon.

and for this reason (and others) gravity waves could provide and excellent long distance communication tool. the range would be essentially infinity. Now, if I could just lay may hands on a quantum black hole (the Tunguska meteorite?) and a strong enough electromagnet to vibrate it with I could obsolete Arrecibo.

 

[Noboundaries]

Okay, I'm going to poop on this party. I skimmed this entire thread and I don't think I saw the word displacement one time. If I missed it, smack me.

The terms positive, neutral, and negative buoyancy are 100% accurate. You are all looking at buoyancy in a manner that is giving me a headache. Here's how it works.

A diver puts on all his/her gear and weighs 200 lbs. Additionally the diver is wearing a wing that when fully inflated will displace 35 lbs of salt water.

He/she inflates their BC and jumps in the ocean. With an inflated wing the diver DISPLACES 235 lbs of salt water. The diver floats and is positively bouyant because they DISPLACE more water than they weigh. This is call positive buoyancy.

He/she deflates their BC so they displace only 200 lbs of salt water. They sink to the top of their head mid breath. The diver is neutrally buoyant, displacing 200 lbs of water.

If the diver breaths in, they displace more water, say 2 more pounds to 202 lbs. The 200 lb diver starts to rise.

Instead the diver blows all the air out of their lungs, collapsing the space they take up in the water, displacing say only 195 lbs of water. The 200 lb diver begins to sink. This is negative buoyancy.

As they sink deeper the pressure of the water collapses their neoprene wetsuit and the space they occupy in the water shrinks, displacing less water weight, say only 185 lbs. Now the 200 lb diver is 15 lbs negatively buoyant and their descent rate starts to accelerate. To stop a runaway descent, the diver adds air to their BC, increasing their space in the water and increasing the weight of the water they displace to say 195 lbs. Now only 5 lbs negatively buoyant, their decent rate is controlled.

As they near the bottom, they add air to their BC to increase the space they occupy in the water, increasing their displacement. When that displacement equals 200 lbs, they are neutrally buoyant.

Breathing in expands their chest, displacing say 202 lbs of total water and the 200 lbs diver begins to rise. Then they breath out and either get back to 200 lbs, or completely empty their chest, displacing less water, say 198 lbs, and the begin to sink.

Displacement my friends is how to understand buoyancy. Gravity and all the other forces, vectors, distances, densities, etc discussed here are merely conditions of the environment for a person's position to the center of the gravitational mass.

Okay, blast me. I can take it! :cool2:

 

[notoriousrook]

i dgaf bout bouyancy, i spent my first few dives literally upside down, fins in the air... or water rather. you get the point

 

[sambolino44]

Calling being out of equilibrium on the heavy side is like calling vacuum negative pressure. It's not absolutely correct in the most precise definition of the terminology, but it's a convenient way for some people to grasp a concept, visualize it, if you will. Sadly, like a lot of our language, the most accurate way of saying something is not the most common. Maybe not so sad with social and aesthetic topics where vagueness, nuance, and flair actually add to the conversation. But in technical terms, well, I think it just reflects the sorry state of education in our country these days.

 

[sambolino44]

Well, that and it's shorter.