Water Temperature Physics

Please register or login

Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.

Benefits of registering include

  • Ability to post and comment on topics and discussions.
  • A Free photo gallery to share your dive photos with the world.
  • You can make this box go away

Joining is quick and easy. Log in or Register now!

From Wiki:

According to 20th century folklore, the laws of aerodynamics prove that the bumble bee should be incapable of flight, as it does not have the capacity (in terms of wing size or beats per second) to achieve flight with the degree of wing loading necessary. The origin of this myth has been difficult to pin down with any certainty. John McMasters recounted an anecdote about an unnamed Swiss aerodynamicist at a dinner party who performed some rough calculations and concluded, presumably in jest, that according to the equations, bumble bees cannot fly. In later years McMasters has backed away from this origin, suggesting that there could be multiple sources, and that the earliest he has found was a reference in the 1934 French book Le vol des insectes; they had applied the equations of air resistance to insects and found that their flight was impossible, but that "One shouldn't be surprised that the results of the calculations don't square with reality".

Some credit physicist Ludwig Prandtl (1875–1953) of the University of Göttingen in Germany with popularising the myth. Others say it was Swiss gas dynamicist Jacob Ackeret (1898–1981) who did the calculations.

In 1934, French entomologist Antoine Magnan included the following passage in the introduction to his book Le Vol des Insectes:

Tout d'abord poussé par ce qui se fait en aviation, j'ai appliqué aux insectes les lois de la résistance de l'air, et je suis arrivé avec M. Sainte-Laguë à cette conclusion que leur vol est impossible.

This translates to:

First prompted by what is done in aviation, I applied the laws of air resistance to insects, and I arrived, with Mr. Sainte-Laguë, at this conclusion that their flight is impossible.

Magnan refers to his assistant André Sainte-Laguë, a mathematician.

It is believed that the calculations which purported to show that bumble bees cannot fly are based upon a simplified linear treatment of oscillating aerofoils. The method assumes small amplitude oscillations without flow separation. This ignores the effect of dynamic stall, an airflow separation inducing a large vortex above the wing, which briefly produces several times the lift of the aerofoil in regular flight. More sophisticated aerodynamic analysis shows that the bumblebee can fly because its wings encounter dynamic stall in every oscillation cycle.

Additionally, John Maynard Smith a noted biologist with a strong background in aeronautics, has pointed out that bumble bees would not be expected to sustain flight, as they would need to generate too much power given their tiny wing area. However, in aerodynamics experiments with other insects he found that viscosity at the scale of small insects meant that even their small wings can move a very large volume of air relative to the size, and this reduces the power required to sustain flight by an order of magnitude.

Another description of a bee's wing function is that the wings work similarly to helicopter blades, "reverse-pitch semirotary helicopter blades".

Bees beat their wings approximately 200 times a second. Their thorax muscles do not expand and contract on each nerve firing, but rather vibrate like a plucked rubber band.
 
There are other factors at work here. True, the "maximum density" info is correct....for water and not water solutions Solution chemistry (and physical properties, such as freezing points and boiling points as well as density) is different for pure substances. Quarry and lake water, while fresh, is not PURE. When substances dissolve in water, the freezing point usually drops. Therefore, it is entirely possible...indeed, likely...that the low temperatures mentioned are completely correct.
 
There are other factors at work here. True, the "maximum density" info is correct....for water and not water solutions Solution chemistry (and physical properties, such as freezing points and boiling points as well as density) is different for pure substances. Quarry and lake water, while fresh, is not PURE. When substances dissolve in water, the freezing point usually drops. Therefore, it is entirely possible...indeed, likely...that the low temperatures mentioned are completely correct.

Are you letting facts screw up a perfectly good theory? Jeez! :)
 
Both my Suunto D3 and Cressi-Sub Archimedes II read a minimum of 37 degrees F after a 40 minute dive at 25 feet.

The dive manuals for both instruments indicate temperature accuracy +/- 2 degrees C (3.6 degrees F) within 20 minutes of temperature change.

So if we are to believe windapp, both instruments, made by two different companies, were off by exactly the same number of degrees, and the error was in the same direction.

Can someone here with a degree in statistics give us a p value for the likelihood of such an event?

I would suggest that this is the result of both manufactures calibrating the same type of sudo-linear (not really linear but linear over a short range) sensor at 68 degrees fahrenheit.
 
There are other factors at work here. True, the "maximum density" info is correct....for water and not water solutions Solution chemistry (and physical properties, such as freezing points and boiling points as well as density) is different for pure substances. Quarry and lake water, while fresh, is not PURE. When substances dissolve in water, the freezing point usually drops. Therefore, it is entirely possible...indeed, likely...that the low temperatures mentioned are completely correct.

Not likely at all. Go to a wine supply store an buy a hydrometer, and two cylinders. Use them to compare the quarry water to distilled water at the same temperature. I challenge you to see the difference. I supposed next we need to have people check the mineral content of the water they are putting in their ponds before they can winter their fish.
 
Have you considered a lake fed by glacial runoff?
 
Both my Suunto D3 and Cressi-Sub Archimedes II read a minimum of 37 degrees F after a 40 minute dive at 25 feet.

The dive manuals for both instruments indicate temperature accuracy +/- 2 degrees C (3.6 degrees F) within 20 minutes of temperature change.

So if we are to believe windapp, both instruments, made by two different companies, were off by exactly the same number of degrees, and the error was in the same direction.

Can someone here with a degree in statistics give us a p value for the likelihood of such an event?

I think that people may still be lacking in understanding. I think it is quite possible that the temperate could be below 4 degrees C at depth. The most dense water is 4 C. As you contiue to cool water below 4 C, the water EXPANDS and becomes lighter.

It is my understanding that it gets progressively less dense the colder it gets as it transitions from 4 to 0 C (freezing). This is where my understanding is a little fuzzy, but in the 0 to 4 C range the water becomes more viscous and the molecules are starting to form molecular aggregations that are precursors to actual crystal formation that happens when the phase change occurs.

No body ever said liquid freshwater can not occur at a temperature below 4 C, it is just that the water is most dense at this temperature... if it is cooled further it floats to the top (as it prepares to freeze).

It is extremely important (from an ecological aspect) that water expands as it cools and freezes. The entire earth's climate and certainly the ecology of freshwater bodies within the upper latitudes would be vastly different if ice sunk like most solids. Even the oceans would be far different if ice sunk.
 
Not likely at all. Go to a wine supply store an buy a hydrometer, and two cylinders. Use them to compare the quarry water to distilled water at the same temperature. I challenge you to see the difference. I supposed next we need to have people check the mineral content of the water they are putting in their ponds before they can winter their fish. Windapp

Actually, I didn't have to go to a store at all...I used the equipment in my science laboratory. The two freshwater samples I used for comparison (to both my local water...Texas...and distilled water) were from Vortex Springs and Morrison Springs in Florida. The salt sample was from just offshore of Destin, Florida. Both fresh samples, though extremely CLEAN, were nowhere CLOSE to distilled values. Both contained organic suspended matter (algae and fish poop?) and significant quantities of carbonates, some phosphates, and even a bit of nitrogenous compounds. They also were fairly loaded with Oxygen and at least some CO2. In short, they had significant chemical and physical differences from distilled water. The sea sample? Well, don't even go there.

A great lab exercise for the environmental science class I teach.
 
Last edited:
Both my Suunto D3 and Cressi-Sub Archimedes II read a minimum of 37 degrees F after a 40 minute dive at 25 feet.

The dive manuals for both instruments indicate temperature accuracy +/- 2 degrees C (3.6 degrees F) within 20 minutes of temperature change.

So if we are to believe windapp, both instruments, made by two different companies, were off by exactly the same number of degrees, and the error was in the same direction.

Can someone here with a degree in statistics give us a p value for the likelihood of such an event?

Doc, from a calibration point of view you are skating on..... thin ice.
 
Well, the logic that as water gets colder than 4 deg C it gets lighter, and that it can't be like that at the bottom of the quarry makes sense: When you look at under ice pictures (never been under the ice intentionally - once in a jeep though), you never see ice forming on the bottom. I would assume that people looking at the computers and seeing temperatures below 4 Deg C might have recorded the temperatures of the water just below the ice.

But we really need to look at this from another point of view: why do we care about if the water is 4 deg C or 3 or even 3 deg C? It's freaking cold no matter how you look at it!!! hehe!
 
https://www.shearwater.com/products/teric/

Back
Top Bottom