Physics Rant: The Truth to Buoyancy in Diving

[Steve_Dives]

Can I refer to my lead weights as antibuoyancy pods?

 

[mwilding]

If I am positively bouyant at 100ft, am I still floating?

 

[ReefHound]

Okay, rant over. I hope I educated at least one of you. Begin the ridicule!

Tom

1st, imprecise use of terms isn't what bothers you geeks the most. It's when those you feel are inferior laugh at your lectures, say you don't know what you are talking about, and everybody sides with them because they are more popular.

2nd, then primary objective of training manuals and classes is to improve the diving skills of divers, not prepare him for a higher score on the SAT. So if using a common term such as "buoyancy" to describe the various states is more effective, then it is also more appropriate.

3rd, buoyancy is not a force, it's the effect of a force. Gravity is the only force in play and the effect is determined by how gravity acts on objects of differing densities.

 

[ReefHound]

Can I refer to my lead weights as antibuoyancy pods?

Sometimes I screw with students by telling them they need to get some neutrally buoyant weights.

 

[J.R.]

If I am positively bouyant at 100ft, am I still floating?

... above or below sea level??

 

[4sak3n]

I'm an engineer and I say shuddup, lets go diving.

I like precise terminology when it's needed, but hate geek-speak otherwise.

+a

...

hold on, I meant: +purple

...

no hold on: +1.

Thats right ... +1.

Precise terminology is just another tool in your [engineering] toolbox. If you don't need to use it, why go out of your way? My professors understand exactly what I mean when I say 'current' even though I should strictly say 'conventional current'.

P.S. Nevertheless loved your rant! Sometimes it just feels goooooood ...

 

[Blackwood]

This isn't a physics discussion. It's a semantics discussion. Divers use the term buoyancy to refer to the sum of the vertical forces, and that's perfectly reasonable.

Respecting a frame of reference (i.e. up = positive (F_buoy) and down = negative (F_grav)) that sum can be neutral (i.e. F_grav = F_buoy), it can be negative (i.e. F_grav > F_buoy), and it can be positive (i.e. F_grav < F_buoy).



If you want to make it into an educational physics discussion, point out the flawed common belief that a diver with positive buoyancy is necessarily moving up in the water column, etc.

 

[4sak3n]

If you want to make it into an educational physics discussion, point out the flawed common belief that a diver with positive buoyancy is necessarily moving up in the water column, etc.

You mean like someone who is positive but angles their scooter downward to compensate and thus stay at a constant depth despite their positive buoyancy?

I think b1gcountry would just say that is exactly what he is talking about. Another discrete force which nevertheless adds to the cumulative effect but is not part of 'buoyancy' ... just like 'buoyancy' isn't technically part of 'buoyancy' either.

 

[b1gcountry]

Thank you for taking the time to write that. I appreciate it. Now that said, don't ever think I will go to the movies with you.

Even worse is going to the movies with me and my wife. She is a NP, so I pick apart the logical errors, and she picks apart the medical miracles ever so popular on modern TV

Tom

 

[Blackwood]

You mean like someone who is positive but angles their scooter downward to compensate and thus stay at a constant depth despite their positive buoyancy?

No, I meant F=ma.

Neglecting things like scooters, upwelling currents, etc., if you have positive buoyancy, your acceleration is positive (upwards), but with no other information, no conclusions can be drawn about your velocity (i.e. it could be downwards).

Vice versa for negative buoyancy.

If you have neutral buoyancy, you aren't accelerating at all in the vertical direction. But that doesn't mean you aren't moving up or down.


There's also drag, which by definition decelerates you regardless of the direction in which you are moving (but doesn't act at all if you are motionless).