To keep your shoes on your feet, for one thing!
It is different in that the seas don't have air pressure. No air; no air pressure.
The sea breeze contains salt water that gets picked up by the wind, moist air is just concentrated air with water vapor and is not salt water.
The backwards knot and forward knot are used in making friendship bracelets. For instructions see the related link below.
yes it is a very loose knot as if you pull the short piece of single rope it will come undone