There are 3 distinct states of matter: solid, liquid and gas. The molecular differences between these states are determined by the ability of their kinetic energies to overcome the forces of attraction among the molecules. Out of them, Gaseous state of matter exhibits the highest degree of freedom for movement in 3 dimensional space. This allows gases not only to acquire the shape of the container but also to adapt its volume to occupy the container as well. Interestingly, these moving gas molecules are responsible for three major phenomena distinct from each other.
While all 3 observations are based simply on motion of gas molecules, they are not necessarily dependent on each other. They can take place at the same as well. For example, a heated windy atmosphere conducts sound without a difference.
Themal Energy
Thermal energy (heat) is a measure of random movement of particles. The average speeds of gas molecules due to heat reaches over 1500 km/h. Our senses pick up these motions as temperature sensations.
Wind
In contrast, Wind represents movement of gas molecules as a bulk (sort of a mass flow) in a more ordered and consistent way. As a result, there is a net flow in a particular direction. Winds have been reported up to speeds of 400 km/h here on Earth.
Sound
Sound on the other hand is ordered particle movements which are oscillatory. Unlike heat, these motions are ordered. And unlike wind, gas molecules don’t move consistently. Instead, they move forwards and backwards about a point. As a result, a fluctuation in the pressure exerted by the gas is observed. This is what our ears pick up as sound. In a normal day, sound can reach over 1200 km/h.
Can We Hear Movements of Gas Molecules?
Not necessarily. Unless there is no fluctuation in pressure, our ears will not be able to make anything out.
Can We Hear Wind?
We don't hear wind itself. What we hear most of the time is due to movements of trees, leaves or dirt. Wind can generate sound when its flow is turbulent and vibrating. This is heard as 'howling' in a steaming kettle for example. Musical wind instruments such as the flute follow a similar principle.
Does Wind affect Speed of Sound?
The speed of sound among air molecules is fairly the same regardless of wind. It means that sound covers the same distance through air. However, when air moves as a whole (that is a wind), it takes the propagating sound with it. This results in a different observed speed by a person on the ground.
Does Temperature affect Speed of Sound?
Yes. According to Kinetic Theory of Gases and the Ideal Gas Law, the speed of sound is directly proportional to the square root of kelvin temperature of the gas.
Can Sound Generate Heat?
Yes. Sound is a form of ordered motion of molecules and heat is the disordered form. As sound moves along, some of the movements are disordered and energy is lost as heat. This results in small fluctuations in temperature. When speed of sound is calculated neglecting this fact, a lower value is obtained. Historically, this was introduced by
Laplace over the calculation by Sir Isaac Newton.
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