Whether it's a gas or a solid, the properties of the pressure are the same, the pressure per unit area. The reason you think solid pressure is easy to understand and gas pressure is hard to understand is that you don't know what the pressure is.
A gas is a group of molecules that are constantly in thermal motion, and these molecules constantly impact the wall of the container containing the gas. When these molecules collide with each other, it is equivalent to applying a force to the vessel wall, although the force is very small and the acting time is very short. But there are too many people, too many gas molecules, they constantly hit the wall of the container, the result is that the pressure on the wall of the container is constant, divided by the area of the wall of the container, that is, the pressure of the gas.
Three laws of gas pressure
Here is a graphic example to further illustrate this pressure:
Everyone has played tug of war. If you pull both sides of the rope at the same time, which side will pull harder, which side will win. It seems that there will be a constant pull rope at both ends, but if we look at the force exerted by an athlete in the process, it is actually discontinuous. This is his foot up and down, pulling the rope, every time he pulls, pulling the rope. But there are a lot of people, and everyone is pulling the rope more frequently, so it looks like pulling the rope constantly and stably.
Every athlete is like a gas molecule, the rope is like the wall of the container, and the tension on the rope is like the pressure on the wall of the container. The force provided by each molecule is discontinuous and the action time is short, but when the number of molecules is large and the frequency is fast, it can be considered that a stable force is provided for the vessel wall.
So the pressure of the gas is equal to the force of the gas molecules hitting the container wall / the area of the container wall
Factors affecting pressure
First, let's decompose the "force of gas molecules hitting the wall", which is equal to the number of molecules hitting the wall in unit time * the force of each molecule. Decomposition is obvious, so I won't go into details.
By substituting the disassembly results into the above formula, we can get:
Pressure = number of molecules hitting the wall in unit time * molecular force / wall area
(note that this is not a formula, it only reflects the factors that affect stress. )
Let's analyze these three factors one by one:
The number of molecules striking the vessel wall in unit time the number of molecules striking the vessel wall in unit time is related to the mass of the gas. The larger the mass of the gas, the more molecules hit the wall of the container in unit time. So we can use mass to express the number of molecules.
Impact force of single molecule: the impact force of single molecule is related to the impact speed. The higher the temperature is, the faster the polymer moves and the greater the impact force is. So you can express the impact force in terms of temperature.
Area of container wall: for simplicity, let's assume that the container is a sphere. The smaller the volume, the smaller the area of the container wall. So we can use volume to express the area of the impact plane.
Based on the above analysis, our formula can be further rewritten as:
The pressure is equal to the mass of the gas times the temperature per volume
(note that its exact formulation is the ideal gas law, PV = NRT, which means the same, but I think it's more intuitive.)
Let's analyze these three laws at the beginning of this article.
Boyle's Law: if the pressure is equal to the mass of gas * temperature / volume, the smaller the volume is, the smaller the denominator is, and the larger the value is.
Charlie's Law: from pressure = gas mass * temperature / volume, the mass and volume remain the same. The higher the temperature is, the larger the molecule is, the greater the value is, that is, the greater the pressure is.
Gay gay lussac Law: if the pressure is equal to the mass * temperature / volume of the gas, if the mass is constant, the pressure must remain unchanged, and the molecule and denominator must be in the same proportion or in a positive proportion to each other. Therefore, when the pressure is constant, the volume is directly proportional to the temperature.
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