Originally Posted by sbratt
Hey bshock. I sit on a jon boat with a large rock in a pond. I throw the rock overboard. Does the pond level go up or down?
Let's think about the kayak. I have 10 gallons of CO2 in my dry bags. Let's say they weigh 2 lbs total. Instead I use He. Now my bags have 2 lbs of lift. I do displace a hair less water (4 lbs). without large volumes, I don't get much.
The pond level goes down. The rock in the boat displaces it's equivalent mass in water. The rock is more dense than water, hence more water volume is displaced when the rock is in the boat. The rock goes over board, resulting in only it's volume displacing water. Thus lower water level.
I agree that the mass of a rock in the jon boat will displace more water than compared to the displacement of its volume (submerged).
Back to helium versues air or CO2 providing more flotation. The volume of the bags/tubes will be constant regardless of the type of gas used. The average atomic mass of helium is 1.0079 which in turn would yield a molar mass of 2.0158 g for atmospheric helium (He2). The molar mass for air is approximately 29.0 g while the molar mass CO2 in 44.0 g. Density is equal to mass/volume. Considering the volume is constant, there is a direct relationship between mass and density. In other words, if the mass is increased coinsiding with constant volume, the density is also increased, resulting in lower flotation. The other variable to consider (that sbratt pointed out) is the mass of the gasses.
I'm really not sure how much difference it would make.
It's 4:00 and school is out....... cheers!!!