There has been a lot of talk about things like pressure, density and viscosity in different threads all over deeperblue. Why not post your questions and thoughts regarding the physics that affect freediving all in one thread?
Here's something that occured to me today:
Eric Fattah among others has written a few times about the difference in viscosity between fresh water and salt water. This reminded me that water temperature also affects it's viscosity. The coefficient of viscosity for pure water at 20' C is about 0.001 Pa s but for pure water at 0' C it is 0.0018 Pa s. That's an 80% increase!
If you move at a relatively low velocity through water, the frictional force is directly proportional to the coefficient of viscosity.
So if you are moving slowly, you would experience 80% more friction in 0' C water as compared to 20' C water!
I don't know if a normal freediving velocity of around 1 m/s would be considered a low velocity in this case, but still it seems that there would be a pretty major difference between warm and cold water.
The density of water also decreases with increasing temperature after 4' C, but the change is nowhere near as dramatic as with viscosity. So from this point of view it would seem that the warmer the water, the better it is for freediving! Less friction and only a fairly minor change in density so there would still be plenty of power in your kicks.
I have never noticed the difference myself, and most likely there is not much of a difference in real life, but it is an interesting idea anyway.
In the summer I freedive in water that might be close to 20'C on the surface and 4'C at 30m. So as I sink deeper, the friction affecting me increases. But at the same time my buoyancy keeps decreasing. At depths less than 30m the change in buoyancy is the dominant factor, but still the situation is more complex than I thought before.
It would be interesting to read comments from others more learned in hydrodynamics.
Here's something that occured to me today:
Eric Fattah among others has written a few times about the difference in viscosity between fresh water and salt water. This reminded me that water temperature also affects it's viscosity. The coefficient of viscosity for pure water at 20' C is about 0.001 Pa s but for pure water at 0' C it is 0.0018 Pa s. That's an 80% increase!
If you move at a relatively low velocity through water, the frictional force is directly proportional to the coefficient of viscosity.
So if you are moving slowly, you would experience 80% more friction in 0' C water as compared to 20' C water!
I don't know if a normal freediving velocity of around 1 m/s would be considered a low velocity in this case, but still it seems that there would be a pretty major difference between warm and cold water.
The density of water also decreases with increasing temperature after 4' C, but the change is nowhere near as dramatic as with viscosity. So from this point of view it would seem that the warmer the water, the better it is for freediving! Less friction and only a fairly minor change in density so there would still be plenty of power in your kicks.
I have never noticed the difference myself, and most likely there is not much of a difference in real life, but it is an interesting idea anyway.
In the summer I freedive in water that might be close to 20'C on the surface and 4'C at 30m. So as I sink deeper, the friction affecting me increases. But at the same time my buoyancy keeps decreasing. At depths less than 30m the change in buoyancy is the dominant factor, but still the situation is more complex than I thought before.
It would be interesting to read comments from others more learned in hydrodynamics.
