is cold water denser than warm?

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”?


"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 …

– Last Updated: Jan-20-09 7:26 PM EST –

..... 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.

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.