Air Pressure + Gravity = Buoyancy - The Principle of Buoyancy and Air Pressure | HowStuffWorks
I was wondering whether it would be possible to generalize about a relationship between gravity and atmospheric pressure in any gravity-well. Hey frndz, Can anyone explain me what is atmospheric pressure? How it acts? And is there any relation between Atmospheric pressure and. atmospheric pressure, gravity, Green's functions. Issue Section: Bermuda sea level in relation to tides, weather and baroclinic fluctuations.,. Rev. Geophys.
Since water is a lot denser than air, in water the pressure changes a lot even for small height differences.
Here's how you can use water to see the way gravity affects pressure. Get an empty 2-liter soda bottle and poke several small holes in it going up the side of the bottle.
Plug all of the holes up you may be able to do this with the needles that you used to make the holes. Fill the bottle all the way up and pull the plugs out.
The water will shoot out of the holes because of the pressure of the water pushing out. The higher the pressure of the water, the farther the water will shoot. What you will probably see is that the water coming out of the bottom holes will shoot farther than the water from the top holes. The pressure of the water is higher as you go deeper into the soda bottle. Its the same reason you feel the pressure on your body in particular your ears rise as you dive to the bottom of a pool.
This is also the reason that human divers can't go below a certain depth in the ocean.
Pressure and gravity
For humans, pressures of more than atm can cause problems, which is equivalent to about meters underwater. Although humans generally don't try to dive this deep, some seals have been known to dive more than meters below sea-level, so that they have to have special adaptations to let them survive at high pressures.
For more info on exactly how to calculate all these numbers, check out the answer to the question. This pressure level is highest right at the surface of the Earth because the air at this level is supporting the weight of all the air above it -- more weight above means a greater downward gravitational force.
As you move up through levels of the atmosphere, the air has less air mass above it, and so the balancing pressure decreases. This is why pressure drops as you rise in altitude. This difference in air pressure causes an upward buoyant force in the air all around us.
Relationship Between Atmospheric Pressure and Surface Gravity
Essentially, the air pressure is greater below things than it is above things, so air pushes up more than it pushes down. But this buoyant force is weak compared to the force of gravity -- it is only as strong as the weight of the air displaced by an object. Obviously, most any solid object is going to be heavier than the air it displaces, so buoyant force doesn't move it at all. The buoyant force can only move things that are lighter than the air around them. For buoyancy to push something up in the air, the thing has to be lighter than an equal volume of the air around it.
The most obvious thing that is lighter than air is nothing at all. A vacuum can have volume but does not have mass, and so, it would seem, a balloon with a vacuum inside should be lifted by the buoyancy of the air around it.
This doesn't work, however, because of the force of surrounding air pressure. Air pressure doesn't crush an inflated balloon, because the air inside the balloon pushes out with the same force as the outside air pushing in.
How Hot Air Balloons Work
A vacuum, on the other hand, doesn't have any outward pressure, since it has no particles bouncing against anything. Without equal pressure balancing it out, the outside air pressure will easily crush the balloon. And any container strong enough to hold up to the air pressure at the earth's surface will be much too heavy to be lifted by the buoyant force.
Another option would be to fill the balloon with air that is less dense than the surrounding air.