Why don t air molecules end up on the earth s surface due to gravity like dust?

The fact that air molecules do not end up on the Earth's surface due to gravity, as dust does, is because air is a mixture of substances, including gases such as oxygen, nitrogen, and carbon dioxide, as well as tiny dust, water vapor, and other suspended solids. These substances also have different rates of sedimentation under gravity due to their respective densities and sizes.

Dust particles are larger, so they settle faster under gravity. In contrast, air molecules have a short average free path, and they collide frequently with surrounding molecules, slowing down the rate of sedimentation. In addition, the movement of air molecules is also affected by the thermal motion and pressure of gas molecules, which further slow down the sedimentation rate of air molecules.

In addition, the movement of air molecules in the upper layers of the Earth's atmosphere is affected by solar radiation and cosmic rays. The combination of these factors prevents air molecules from eventually falling to the Earth's surface due to gravity, as dust does.

First of all, there is no such thing as an air molecule, air is a mixture, made up of a variety of substances;

Then, gravity has an effect on the air, which is manifested in the fact that the air density on the surface of the earth is greater than that of the air at the top;

Finally, part of the gravitational force is to provide the centripetal force.

In addition to the gravitational force, there is also a force in the gas molecules that act on each other, and this force is more dominant than the gravitational force. When the molecules are close to each other, they produce repulsive force, and when they are far away, they become gravitational force.

The earth's surface is full of air, and if all the air molecules fall to the ground, then the thickness of the air can be infinitesimal.

The movement of house dust is the result of the combined action of gas and gravity, so it is not correct to say that the movement of house dust is caused by the collision of air molecules with dust.

Question B Analysis: Reading through the passage, this article is an explanatory passage that explains the reason why "the sun looks dark yellow and red at sunset and sunrise", and it is written in a logical order. If you know what you are writing, it is not difficult to make it clear that it should be the last sentence; The reason for this phenomenon was discovered by astronomers, hence the first sentence; "Rayleigh the British scientist" corresponds to "the astronomer" in the middle, which should be followed by the following; The "short-wave light" in corresponds to , so it should be ranked last; In "yellow, red" corresponds to , so it should be before , then the table reason, so before .

So the correct word order should be:

The intermolecular force is microscopic, and the direction of the force is random and uncertain, and the atmospheric pressure is a macroscopic force, which is simply the force produced by the gravity of the air.

The fundamental cause is still caused by the gravity of the atmosphere, the macroscopic state can affect the motion state of the microscopic molecules, and the collision frequency and average free path of the air molecules are affected by the gravity of the atmosphere.