If everything falls down with acceleration g, why molecules of air do not?

Answer 1

They do. However, they are so light that they are pushed back up by pressure/currents, etc. In short, the air itself keeps the air up there!

Same reason a feather and a bowling ball don't fall at the same rate if dropped off a building, but they would in a vacuum,

Answer 2

They would if the other air molecules below them weren't in the way. Air is acted on by the same forces as everything else but is so light the it requires almost no force to hold oppose gravity. That force is provided by the air underneath it. That is why air pressure is higher near the surface of the earth than way up in the atmosphere. The additional pressure at the surface is caused by the air higher up in the atmosphere pushing down.

Answer 3

gravity is the weakest of the 5 fundamental forces

Electromagnetism is a much stronger force than gravity. Solid objects can not pass through each other because the electrons in their atoms repel each other like tiny magnets. A gas is made of of billions of billions of tiny molecules traveling around as fast as bullets. They are constantly colliding with everything around them and bouncing around like popcorn popping. They have so much energy, gravity can't pull them down. If the loose energy, at some point, they become liquid and even solid. Gravity can then drag them to the floor as a mass, but it can not drag them through the floor. The bouncing gas molecules have kinetic energy and the average kinetic energy is known as temperature. Heat is nothing more than how hard molecules are colliding with each other.

Answer 4

They are, but they are dense enough that not every molecule can keep falling. Imagine air molecules as grains of sand in an hourglass. The grains at the top are just as affected by gravity as the ones at the bottom, but the normal forces of the grains underneath them prevent them from falling to the bottom of the hourglass.

Answer 5

Maxime J is correct, the law of gravitational attraction applies for objects in free fall WHICH ARE SOLIDS. Gas behaves differently and due to motion of particles has what is called vapor pressure... or the resistance to compact. (the vapor pressue in a balloon, for example, is what causes it to expand until the stretch of the rubber counteracts the pressure in the balloon and it stablizes at a certain size).

Like the balloon situation, air around the earth works in reverse. The attraction of gravity gets stronger as you get closer to the surface of the earth... so that is why you end up with air pressure of roughly 15 psi. The vapor pressure of the air, at that point, is enough to counteract gravity. Higher up (like the top of Mt Everest) the attraction of gravity is relatively much less. As such, not as much vapor pressure is needed to counteract gravity (plus it's getting pushed up by the "expansion" of the vaporous air below it) and so the air is "thinner." Going VERY high up requires oxygen tanks in order to breath. That is because with the reduced force of gravity holding the air down, the same AMMOUNT of air, takes up a greater volume.

Answer 6

Pressure.
Gas molecules are highly energetic and they never stop moving and hitting everything and other molecules of gas... They can't all be contained in a restrained area if there is no artificial pressure applied.

MJ

Answer 7

They do. That is why we have air pressure at the surface of the earth of 14.7 psi. If they did not, our atmosphere would just float away into outer space and we would not be here. That is why Hydrogen and Helium "float"; They are really just like bubbles in the sea floating to the surface and a blimp or hot air baloon is like using a float underwater to lift something that is heavier than water.
Light gases don't float out of the atmoshpere though, they just go to the surface of the atmosphere where they are held at high altitudes.

They are all piled up on top of each other just like the water in the ocean. That is why the higher you go on the earth, the less the air pressure. Sea level earth is a typical maximum that is found at all of the beaches in the world, but the "Marianas Trench" of the atmosphere on earth is really in the Dead Sea with a pressure of up to 15.45 psi, compared to about 12 psi for Denver or 4.5 psi on top of Mount Everest.

**Maxime J does not realize that it is GRAVITY that causes pressure.

**PROMETHIUS does not realize that piling liquids on top of each other causes greater pressure at the bottom. The pressure in the ocean is not from the increase (to any significance) in gravity with depth, it is from the height of the column of water above it, just as in the atmosphere where the average weight of a column of air at sea level requires 760 mm of Hg to counteract the weight of that mass.

The gravitational difference in between sea level and the top of Mount Everest is just 9.81 to about 9.77m/s^2. How can that change 14.7 pounds to 4.5 pounds?? Hit edit and reply...

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Answer 8

air molecules are on top of each other. there is no vacuum for them to fall.