But the atoms have a range of speeds, some moving fast and some moving slow. So T relates to the energy content of the gas.
Gas pressure relates to the force from the particle collisions.
More generally, pressure is the spread of the force over area, or force per unit are, hence Density is the amount of matter in a given volume. For a volume V containing a number of particles , the number density is Alternatively, one can speak of mass density , which would be given my the amount of mass M per volume. For a gas, the mass , so For a gas, the pressure, density, and temperature are generally related. The Doppler shift refers to how the frequency, wavelength, and energy of light appears to change when the source and detector are in relative motion. The formula is where , with being the observed wavelength of light and the original wavelength when emitted by the source.