# Motion of Particles in an Ideal Gas

In a gas, unlike in a solid or a liquid, the particles (atoms or molecules) are relatively far away from each other. The chaotic motion of the gas particles is to be illustrated here in a simulation. Thereby, the model of an ideal gas is taken as a basis. The following assumptions are made:

• No force acts on a single particle as long as it does not collide with a wall or with another particle. Therefore, the particles in general move uniformly, i.e. in a straight line with constant speed.
• The collisions are elastic.
• The volume of the particles is neglectable compared to the total volume.
• Rotation and vibration processes are irrelevant.

The control panel of this app has two buttons. The first one ("Reset") creates the initial state, the second one ("Start/Pause/Resume") can be used to start, stop or continue the animation. The option "Slow motion" will decelerate the animation. The type of gas can be selected from four examples, namely nitrogen (N2), oxygen (O2), argon (Ar) and hydrogen (H2). A numerical input is possible - within certain limits - for the amount of substance (a measure for the number of particles, unit mole), the absolute temperature (unit Kelvin) and the pressure (unit kilopascal). The inputs are to be confirmed with the Enter key. Below the input fields, the calculated volume is displayed (unit cubic centimeter). In some cases, the pressure is modified to give a volume between 100 cm3 and 1000 cm3. The radio buttons in the lower part of the control panel determine what will be displayed in the drawing area:

• Animated illustration of the particle motion in a cube-shaped container with edge length 10 cm; of course, the number of represented particles is much smaller than the real number (1 mole corresponds to about 6 × 1023 particles). The blue arrow in the center of the lid illustrates the force required to hold the lid at a constant height.
• Diagram for the probability distribution of a velocity component (vx, vy, or vz)
• Diagram for the probability distribution of the velocity magnitude v (Maxwell-Boltzmann distribution)

Note: For older computers, problems with the computing speed may occur.

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