This additional matter will affect the mass density of the air (an inertial property). As it does, particles of gaseous water become mixed in the air. Like any liquid, water has a tendency to evaporate. Humidity is the result of water vapor being present in air. The speed of a sound wave in air depends upon the properties of the air, mostly the temperature, and to a lesser degree, the humidity. This is mostly due to the lower mass of Helium particles as compared to air particles. Thus, a sound wave will travel nearly three times faster in Helium than it will in air. A sound wave will travel faster in a less dense material than a more dense material.

However, within a single phase of matter, the inertial property of density tends to be the property that has a greatest impact upon the speed of sound. As stated above, sound waves travel faster in solids than they do in liquids than they do in gases. The greater the inertia (i.e., mass density) of individual particles of the medium, the less responsive they will be to the interactions between neighboring particles and the slower that the wave will be. The density of a medium is an example of an inertial property. Inertial properties are those properties related to the material's tendency to be sluggish to changes in its state of motion. Even though the inertial factor may favor gases, the elastic factor has a greater influence on the speed ( v) of a wave, thus yielding this general pattern: v solids > v liquids > v gases For this reason, longitudinal sound waves travel faster in solids than they do in liquids than they do in gases. In general, solids have the strongest interactions between particles, followed by liquids and then gases. The phase of matter has a tremendous impact upon the elastic properties of the medium.

Rigid materials such as steel are considered to have a high elasticity. When a force is applied in an attempt to stretch or deform the material, its strong particle interactions prevent this deformation and help the material maintain its shape. At the particle level, a stiff or rigid material is characterized by atoms and/or molecules with strong attractions for each other. Steel is considered to be a stiff or rigid material, whereas a rubber band is considered a flexible material. A small stress on the rubber band causes a large deformation. On the other hand, a material such as a rubber band is highly flexible when a force is applied to stretch the rubber band, it deforms or changes its shape readily. Steel is a rigid material with a high elasticity. A material such as steel will experience a very small deformation of shape (and dimension) when a stress is applied to it. Elastic properties are those properties related to the tendency of a material to maintain its shape and not deform whenever a force or stress is applied to it. Typically there are two essential types of properties that affect wave speed - inertial properties and elastic properties. The speed of any wave depends upon the properties of the medium through which the wave is traveling.

Faster waves cover more distance in the same period of time. A slower wave would cover less distance - perhaps 660 meters - in the same time period of 2 seconds and thus have a speed of 330 m/s. If a sound wave were observed to travel a distance of 700 meters in 2 seconds, then the speed of the wave would be 350 m/s. The faster a sound wave travels, the more distance it will cover in the same period of time. In equation form, this is speed = distance/time Since the speed of a wave is defined as the distance that a point on a wave (such as a compression or a rarefaction) travels per unit of time, it is often expressed in units of meters/second (abbreviated m/s). Always be cautious to distinguish between the two often-confused quantities of speed ( how fast.) and frequency ( how often.). While frequency refers to the number of vibrations that an individual particle makes per unit of time, speed refers to the distance that the disturbance travels per unit of time. Like any wave, the speed of a sound wave refers to how fast the disturbance is passed from particle to particle. As one particle becomes disturbed, it exerts a force on the next adjacent particle, thus disturbing that particle from rest and transporting the energy through the medium. A sound wave is a pressure disturbance that travels through a medium by means of particle-to-particle interaction.

Speed of sound feet per second