Sudden and uncontrolled acsent.

[Blackwood]

Are you serious??? You really believe that statement!?

Of course.

The buoyancy of the tank = the volume of the tank * the density of the fluid in which it is submerged * the acceleration of gravity.

Unless you change the geometry of the tank or alter the density of the water or change the acceleration of gravity (none of which will happen to any noteworthy amount), the buoyancy of the tank will remain the same (Vρg=Vρg). You could fill it with lead, sand, pizza sauce, helium, etc., and its buoyancy won't be affected. Its weight will.

 

[pants!]

Of course.

The buoyancy of the tank = the volume of the tank * the density of the fluid in which it is submerged * the acceleration of gravity.

Unless you change the geometry of the tank or alter the density of the water or change the acceleration of gravity (none of which will happen to any noteworthy amount), the buoyancy of the tank will remain the same (Vρg=Vρg. You could fill it with lead, sand, pizza sauce, helium, etc., and its buoyancy won't be affected. Its weight will.

You're pretty.... well, wrong.

A tank is a rigid container. Its displacement is constant.

An object with a constant displacement but varying weight has varying buoyancy.

An Al80 full of air weighs about 6 pounds more (has ~ 3 kg more mass) than an Al80 that is completely empty.

Thus, when underwater, a full Al80 will be 6 pounds more negatively buoyant than an Al80 that is empty.

If you don't believe me, toss a full Luxfer 80 and an empty Luxfer 80 into your local pool. Watch what happens, then come back and say they have the same buoyancy

 

[H2Andy]

You could fill it with lead, sand, pizza sauce, helium, etc., and its buoyancy won't be affected. Its weight will.

ah.. but if its weight changes, doesn't that mean that its bouyancy changes too?


(someone explain to me me why i'm jumping back in on this)

 

[pants!]

ah.. but if its weight changes, doesn't that mean that its bouyancy changes too?


(someone explain to me me why i'm jumping back in on this)

Andy... go back to sleep, or you will end up convincing Blackwood that big hunks of steel are, in FACT, quite heavy.

 

[H2Andy]

you will end up convincing Blackwood that big hunks of steel are, in FACT, quite heavy.

you would think that, wouldn't you? and in fact, after several hours of
posting, i would be able to prove it with equations and diagrams much
to anybody's satisfaction

 

[Blackwood]

You're pretty.... well, wrong.

A tank is a rigid container. Its displacement is constant.

An object with a constant displacement but varying weight has varying buoyancy.

An Al80 full of air weighs about 6 pounds more (has ~ 3 kg more mass) than an Al80 that is completely empty.

Thus, when underwater, a full Al80 will be 6 pounds more negatively buoyant than an Al80 that is empty.

If you don't believe me, toss a full Luxfer 80 and an empty Luxfer 80 into your local pool. Watch what happens, then come back and say they have the same buoyancy

No, I'm not wrong.

The buoyant force of a submerged object is the force acting on that object opposite to the direction of gravity equal in magnitude to the weight of the displaced fluid.

As you said, "A tank is a rigid container. Its displacement is constant."

And if that constant displacement tank is submerged in a constant density fluid in a constant acceleration of gravity environment, its buoyancy is constant. Period.

As I said in a previous post, I'm talking about buoyancy, not the relationship between weight and buoyancy.

Eureka!

 

[Soggy]

The buoyant force of a submerged object is the force acting on that object opposite to the direction of gravity equal in magnitude to the weight of the displaced fluid.
....
And if that constant displacement tank is submerged in a constant density fluid in a constant acceleration of gravity environment, its buoyancy is constant. Period.

Yes, but if the WEIGHT of the constant displacement object changes, as happens with a scuba tank, the BUOYANCY of the object changes, per your first line.

An object is positively buoyant if it weighs less than the volume of liquid it displaces and negatively buoyant if it weighs more than the volume of liquid it displaces. Buoyancy and weight are inseparably connected.

Perhaps we are arguing semantics. I see you are an aerospace engineer, thus I'm sure you have a pretty firm grasp of these concepts.

 

[Blackwood]

Yes, but if the WEIGHT of the constant displacement object changes, as happens with a scuba tank, the BUOYANCY of the object changes, per your first line.

No. My first line relates to the weight of the displaced fluid, not the weight of object.

An object is positively buoyant if it weighs less than the volume of liquid it displaces and negatively buoyant if it weighs more than the volume of liquid it displaces. Buoyancy and weight are inseparably connected.

Again, we're talking about different things. You're talking about the relationship between buoyancy and weight. I'm talking about the buoyant force. They are independent.

 

[Blackwood]

Perhaps we are arguing semantics. I see you are an aerospace engineer, thus I'm sure you have a pretty firm grasp of these concepts.

That's probably my problem. I see buoyancy as fluiddensity*objectvolume*gravitationalacceleration.

Divers see buoyancy as (fluiddensity*objectvolume*gravitational acceleration)-(objectmass*gravitationalacceleration)

I'm an engineer first and a diver second.

 

[Soggy]

Again, we're talking about different things. You're talking about the relationship between buoyancy and weight. I'm talking about the buoyant force. They are independent.

Right, we're talking about the buoyancy characteristics of an object submerged in water...you're talking about the buoyant force itself, which is kind of irrelevant to our discussion.