Try it and explain what happens. When you move the air at higher velocity, that means the pressure is lower between the sheets of paper. By taking off into the wind, pilots can increase the velocity of the air over the wings. This increased velocity means decreased pressure on top of the wings, which means the lift force is greater. If planes were to take off with the wind behind them, they would have to move much faster to get off the ground.
Salt water has a higher density than fresh water.
This means that the bouyant force on you in salt water is larger than the bouyant force in fresh water. A bigger bouyant force means you float more easily. As the weather balloon rises through the air, the air pressure decreases. Though the air pressure outside the balloon decreases, the helium inside is still at normal air pressure. Since there is lower pressure outside the balloon than inside the balloon, the walls of the balloon move outward towards the lower pressure.