density
http://www.madsci.org/posts/archives/1999-11/943405321.Ch.r.html
i was thinking , since its a proven fact that atoms slow down as they get colder, could it be that cold water moves slower , ie: it takes the water molecules more time to move out of the way and this is what slows down a object in cold water ? I’m not a scientist or a hydrologist but it’s known everything slows down the colder it gets, the answer to why you slow down in cold water probably lies on a molecular level, also your own muscles do not operate at peak in cold temps. also i was thinking …is there more “sticktion” from cold water than warm water? i know the colder it gets the slower i get! if you take it to a extreme …cold, slushy water does not flow as easily as warm water. i tried to google up a better answer and didn’t get much.
That’s a joke, right?
I sure hope so.
winter paddling at slower pace?
I’ve noticed that cooler water tends to be slower, too. Also, wearing bundles of clothing in the winter restricts movement, especially neoprene gloves and westsuits. The “experts” - elite paddlers will confirm that cold water is slower paddling than warm water. I don’t understand the complete factors. Also, warm salt water is faster paddling than a similiar temp freshwater. A major speed limitation is shallow water - generally less than .5 waterline length will slow you down. As the water gets down to less than 5-6 feet, it becomes very rapidly more difficult to maintain speed.
Viscosity
Water that is about 35 degrees is about twice as thick as water that is 75 degrees. It is easy to test the viscosity for yourself with simple equipment you can make.
The difference in density or weight per unit volume across the temperature range is very slight, but the viscosity difference is huge.
People naturally understand this with honey or oil, but since water still pours well out of a pitcher when is is icy, folks don’t think of it as being thicker, but it is.
Hot water tank…
…from olden, or modern if you have the stove for it, days is a good example. Pipe comes from bottom of tank into stove, where water warms it, water expands so same amount of water is lighter and rises, and travels up the pipe to the top of the water tank and is replaced by the cool water that keeps coming in from the bottom of the tank. After a while the water in the top of the tank gets so da$%#& hot that it starts to boil unless you drain it off.
Water as it cools continues to contract, or get more dense, until the point where it solidifies at which time it expands slightly. Good example is those in the frozen north who forget to put antifreeze in their car/truck/etc. cooling system. Result is cracked rads, busted engine blocks from the solid water expanding as it freezes, and then again as it starts to melt.
However, Elmo has the numerical proof.
Only as it freezes initally
Everyone knows …
… that a polyethylene beverage bottle, even one filled to the brim with water, will float in a lake, as the plastic itself is slightly buoyant. So imagine my surprise last summer when my freshly filled water bottle slipped from my deck bungees and promptly sank like a stone.
All I can figure is that the very cold tap water with which I’d filled the bottle was denser than the lake’s surface water, lending it enough negative buoyancy even to offset the buoyancy of the plastic bottle, and taking the whole works down. (Note that there was NO air space inside the bottle.)
I presume that the bottle continued to sink until it reached deeper waters cold enough to match the density of the water in the bottle, where it stopped. Probably when the water temp inside the bottle equalized with that of the surrounding lake water, the buoyancy of the plastic bottle was enough to raise it a little higher, whereupon it equalized with the slightly higher and warmer water, and so on until it slowly and finally reached the surface, buoyed only by the plastic of the bottle itself.
I didn’t wait around long enough to see …
Delphinus
http://www.AquaDynology.com
perhaps this will help answer some …
… of the questions regarding water in reference to it’s temperatures and weight variations .
(bear in mind that different waters will have different specific weights depending on compositions … example being sea water compared to fresh water , etc.)
http://www.engineeringtoolbox.com/water-specific-volume-weight-d_661.html
now viscosity and hydrostatic properties of water can become much more brain twisting when attempting to relate how those properties affect a paddler with a paddle .
http://en.wikipedia.org/wiki/Viscosity
Delphinus , love the bottle example !!
It is, but not enough to notice
It can be measured with a hydrometer, but isn’t going to be enough of a factor to really affect something like that in a noticeable way.
Intermolecular space is not air
Planes need additional runway
for take-offs in hot weather due to less air density for lift and less oxygen available for combustion. Some piston-engined military aircraft used water injection to cool the intake air and develop more HP.
I wonder if teh denser cold air offered added lift for teh US Airways “glider”?
Jim
"Hot and High"
Is the aviation term for locations where aircraft are taxed due to the low density of air, either because it is hot or because of the altitude, as well as aircraft built to operate in such conditions. Of course, air is a gas, so it is compressible, therefore prone to wide swings in density with different temperatures. Water is, for all practical purposes, not compressible, so conversely, it is not going to vary its density greatly with temperature.
I’m denser when I’m cold.
it is called Density Altitude and is …
..... a preflight calculation for departure and landing airports (and req. alternates)... must be factored into flight plan , FAA regs. require the pilot to do so .
Again each aircraft has the numbers for calculations in the performance section of it's operations manual . The pilot is required to know the runway(s) of intended use and their lengths for each landing and takeoff ... and the amount of runway that will be used up by the airplane , which of course temperature and altitude are factors , as well as takeoff weight of the airplane .
There are different types of takeoffs and landings available to a pilot for a given airplane ... some use less runway , others climb a greater height in shortest distance etc.
Climb performance is also affected by Density Altitude . If you are taking off from a high density altitude runway (hot day-high mountain) , and the runway is short or marginal with steep elevations surrounding , you better have your numbers correct and do extra considerations for the departure phase of the flight .
Temperature and humudity also affect "True Altitude" and "True Airspeed" . These are refined by pilot calculation from what the instruments (Altimeter and Airspeed Indicator) are indicating ... the Altimeter is adjusted by the pilot to local baro. pressure for the area of flight and then if needed the refinement calculations ... 1/10 an inch of mercury in the Altimeters baro. window , is worth 100' if the Altimeter has not been set correctly .
Thanks for posting that
I do get my laughs from some of the Science found on Pnet.
question
Right, pure ice would still float in pure water due to lower density. However, this does raise an interesting question.
Most water in the real world is not pure, but contains dissolved oxygen, and presumably other dissolved gases as well. I think warmer water holds more than cold. I forget exactly how it (dissolving) works, but isn’t there some kind of loose bond or association between the different molecules, where some number of h2o associate with a definite number of o2 molecules (for a given temp and pressure)?
So then, what happens to the dissolved gases when the water freezes? Are they “squeezed out” somehow, or do they pool together and some get trapped in tiny bubbles, or do they maintain that loose bond that developed in the dissolving process?
A related (or maybe the same) question is this - is all ice found in the world pure h20? Or are there different types of ice, like water (in the way the freshwater and seawater are referenced below), that contain other substances and so have slightly different weights and densities?
gasses are more soluble in colder h2o
Let me guess
The “expert” was on Fox, wasn’t he.
Water injection:
As a retired pilot, I had to address this. But I had to go back to the books, first!
From PWA OI 200, “The Aircraft Gas Turbine Engine and its Operation”
published by Pratt & Whitney:
The sensitivity of gas turbine engines to compressor inlet temperature
results in appreciable loss of the thrust (or power, in the case of a
turboprop) which is available for takeoff on a hot day. It is frequently
necessary, therefore, to provide some means of thrust augmentation for
nonafterburning engines during takeoff on warm or hot days. This is also
the case on at least one afterburning engine. Ten to thirty percent
additional thrust (power) can be gained by injecting water into the
engine, either at the compressor air inlet or at some other point, such as
the diffuser case. In a piston engine, during power augmentation by means
of water injection, the water acts primarily as a detonation suppressor
and a cylinder charge coolant. Induction air cooling is secondary.
Higher takeoff horsepower results chiefly because when water is added, the
engine can operate at the fuel/air ratio that will produce “best power.”
Sometimes a higher manifold pressure may be obtained than would otherwise
be possible without experiencing detonation. Jet engines, however, have
no detonation difficulties. When water is added, thrust or power
augmentation is obtained principally by cooling the air entering the
engine, by means of vaporization of the water introduced into the
airstream. Cooling the air has the effect of reducing the compressor
inlet temperature. The reduction in temperature increases the air density
and the mass airflow. More and cooler air to the burners permit more fuel
to be burned before limiting turbine inlet temperatures are reached,
which, in turn, means more thrust.