Speed of Sound and Temperature
With an increasing temperature, the speed of sound
increases until it reaches a maximum value at a certain
temperature.Above this temperature the speed decreases . Why does
the speed decrease above this temperature?
Temperature indicates the random bouncing around of the molecules in a
material. As temperature increases, so does the amount of motion: the
molecules crash together more often, and in less organized patterns.
This is how heat energy moves through a material. The faster molecules
give energy to the slower molecules. Sound is an organized pattern of
motion. As the molecules move back and forth together, they transfer
the pattern through the material.
When a material is very cold, the molecules do not move very fast. Even
the energy of the sound wave cannot speed them up much. As the
temperature rises, the molecules speed up. This transfers the sound
pattern through the material more quickly. When a material is very hot,
the molecules already have so much energy that the sound energy makes
very little difference. The disorganization of the motion increases the
time needed for the sound pattern to transfer from molecule to molecule.
This then slows the speed of sound.
Dr. Ken Mellendorf
Illinois Central College
You did not specify whether you are referring to the state of the substance
-- solid, liquid, or gas -- nor the temperature range. Without that info
it is not possible to "explain" the observation.
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Update: June 2012