How Does Altitude Affect the Weight of Water?

[yenting]

water has a density of 62.4lbm/ft^3 .How much does 2ft^3 of water weight at sea level and in Colorado where the altitude is 5374ft and the gravitational acceleration is 32.139ft/s^2?
Solution :

density=mass/volume
62.4lbm/ft^3=mass/2ft^3
mass=124.8lbm

w=mg
=124.8lbm*32.174ft/s^2
=4.015*10^3lbf (sea level)

w=mg
=124.8lbm*32.139ft/s^2
=4.011*10^3lbf (Colorado)

is that correct?

 

[apelling]

Yes it is.

 

[SteamKing]

Sorry, you are both wrong. According to your calculation, yenting, one cubic foot of water weighs about two tons.

One lbm is equivalent to about 0.454 kg. One lbm also has a weight of one pound force when g = 32.174 ft/s^2.

 

[apelling]

Thanks for checking SteamKing.

I'll stick to metric, it's so much easier.

So its the ratio 32.139:32.174 that gives the value of g. That makes much more sense.

 

[rwisz]

Yes, your calculations are correct. The weight of 2ft^3 of water at sea level is 4.015*10^3lbf and at an altitude of 5374ft in Colorado is 4.011*10^3lbf. This is due to the decrease in gravitational acceleration at higher altitudes, which results in a slightly lower weight for the same volume of water.