Rocket Ascents... Can divers breach like a fish (split from Accident in Mich)

[OWSI176288]

Enough math and theory, how about some actual testing.....

Fill a drysuit with water equal to 150lbs on land (water weight is obviously neutral in water). Exhaust valves should be in the fully closed position. Use dry gloves to seal the wrist and duct tape a water filled 2 liter bottle into the latex neck seal. Attach tank with back plate and harness, don't forget the crotch strap. Rig inflator to stick open once inflation begins. Bring the entire mess underwater and try your best to get lift off. If the inflator rigging is to big a bother, use a lift bag. Make sure to have a witness with a video recorder on the surface. Someone really needs to try this, it could be as big as the exploding tank thread!

Sounds like a good episode for the cable TV show "Myth Busters"

 

[Rec Diver]

83 feet in 10 seconds does indeed give you 5.65 (well, 5.66) miles per hour.

That has no bearing on how much it actually takes you to breech the water, though.

Pants, you are exactly correct. What cause anything to breech the water, or even move for that matter, is energy. Energy is a combonation of speed and weight. All things being equal, the same amount of energy can be transfered with more weight and less speed or vice versa. Do you remeber your open water class? Do you remember Acramedies law for water, I think that is spelled right, and why he could float in his bath tub? I am sure there is a Physics major out there somewhere that can make this calculation.

 

[pants!]

I was a physics major in college

There are a couple of components to this. The first is the amount of thrust able to be generated by the fins while kicking. Your example, a stuck inflator valve, assumes the dude was not kicking hard straight up so it can be discounted.

Once the guy leaves the surface of the water, there is no more force acting on him except gravity. If we assume that the downward force of the weight of the human + gear that are currently out of the water balances with the buoyant force of the inflated drysuit below the water equalizes when he is about chest-deep, then the diver has an additional 5 or 6 feet to rise before his fins clear the water's surface.

Neglecting additional water drag while the fins are being lifted out of the water, any negligible lift created by the legs of the drysuit, and a host of other things, the diver will need to clear the surface of the water at more than 12 mph, or 17 feet per second.

I can't believe I actually typed all of this out. The whole idea is one of the dumbest things I've ever heard.

You'd have better luck making a bus jump a 120' long gap in a bridge like you saw in Speed. Oh, wait... you thought that was really possible, didn't you?

 

[mstudley]

Energy is a combonation of speed and weight. All things being equal, the same amount of energy can be transfered with more weight and less speed or vice versa. Do you remeber your open water class? Do you remember Acramedies law for water, I think that is spelled right, and why he could float in his bath tub? I am sure there is a Physics major out there somewhere that can make this calculation.

ugh......

Energy is the capacity of a physical system to do work

Weight != Mass
weight == the vertical force exerted by a mass as a result of gravity
mass == the property of a body that causes it to have weight in a gravitational field

Archimedes' principle: The buoyant force is equal to the weight of the displaced fluid

You need one of these:

 

[Rec Diver]

I was a physics major in college

There are a couple of components to this. The first is the amount of thrust able to be generated by the fins while kicking. Your example, a stuck inflator valve, assumes the dude was not kicking hard straight up so it can be discounted.

Once the guy leaves the surface of the water, there is no more force acting on him except gravity. If we assume that the downward force of the weight of the human + gear that are currently out of the water balances with the buoyant force of the inflated drysuit below the water equalizes when he is about chest-deep, then the diver has an additional 5 or 6 feet to rise before his fins clear the water's surface.

Neglecting additional water drag while the fins are being lifted out of the water, any negligible lift created by the legs of the drysuit, and a host of other things, the diver will need to clear the surface of the water at more than 12 mph, or 17 feet per second.

I can't believe I actually typed all of this out. The whole idea is one of the dumbest things I've ever heard.

You'd have better luck making a bus jump a 120' long gap in a bridge like you saw in Speed. Oh, wait... you thought that was really possible, didn't you?

Now Pants, I am disappointed that you would try to insult me with that last line. But I have to ask, if you were a Physics major in college then why didn't you know how I had arrived at 5.65 MPH?

 

[pants!]

Now Pants, I am disappointed that you would try to insult me with that last line. But I have to ask, if you were a Physics major in college then why didn't you know how I had arrived at 5.65 MPH?

I had assumed you had calculated it as the velocity necessary to fully breech the surface.

I did not think that you simply converted a random number someone else had pulled out of the air.

Silly me :14:

 

[adurso]

Pants, you are exactly correct. What cause anything to breech the water, or even move for that matter, is energy. Energy is a combonation of speed and weight. All things being equal, the same amount of energy can be transfered with more weight and less speed or vice versa. Do you remeber your open water class? Do you remember Acramedies law for water, I think that is spelled right, and why he could float in his bath tub? I am sure there is a Physics major out there somewhere that can make this calculation.

Archimedes Law: A body submerged in a fluid experiences a buoyant force equal to the weight of the displaced fluid. Displacement has nothing to do with breaching.

Energy (physics def):The capacity for doing work. Forms of energy include thermal, mechanical, electrical, and chemical. Energy may be transformed from one form into another.

Energy is not a combination of speed and weight. Energy in one form or another is what causes speed, actually velocity, or acceleration.

Weight does not enter into the calculation because weight is not a constant. Mass is the constant, mass remains the same under water, in space or at 1ATA.

This keyboard does not have the symbols I need, so I will not bore everyone with the equations, suffice it to say incorporating the drag coefficiency of water and average mass of a human being with the inherent drag of scuba equipment in a Euclidian Universe average humans cannot loft themselves from the depths their body length into the air.

I do not discount the possibility of this occurrence in a Non-Euclidian Universe nor in a universe governed by physical laws other than those we are familiar with on this planet.

 

[TCDiver1]

I agree with Pug. This turbulent discussion, while entertaining, has been a real drag. Hydraulically speaking of course.

 

[Rec Diver]

ugh......

Energy is the capacity of a physical system to do work

Weight != Mass
weight == the vertical force exerted by a mass as a result of gravity
mass == the property of a body that causes it to have weight in a gravitational field

Archimedes' principle: The buoyant force is equal to the weight of the displaced fluid

You need one of these:

Matt, according to Albert Einstein...E=MCsquared. M being the mass and C being the velocity. Energy is what is required to move an object. Einstein also concluded that for every force in one direction there is also an equal force in the opposite direction. If you apply Einsteins theroy of relativity and Archamedes principle, thank you for correcting my spelling, I believe you will find that the water will actually help displace a diver, not hinder them

 

[Rec Diver]

Archimedes Law: A body submerged in a fluid experiences a buoyant force equal to the weight of the displaced fluid. Displacement has nothing to do with breaching.

But it does affect how qucky you are displaced, thus being velociy.

Energy is not a combination of speed and weight. Energy in one form or another is what causes speed, actually velocity, or acceleration.

Albert Einsteins law of energy E=MCsquared. Meaning....Energy equals the mass of an object multiplied by the velocity the object is moving squared. Actually energy is in fact a combonation of speed and weight.

oes not enter into the calculation because weight is not a constant. Mass is the constant, mass remains the same under water, in space or at 1ATA.

Weight is mass and mass is weight. It has everything to do with the energy required to move an object

I do not discount the possibility of this occurrence in a Non-Euclidian Universe nor in a universe governed by physical laws other than those we are familiar with on this planet.

Sorry, you losted me on this one.