Sound waves traveling in fluids, such as air and water,
are longitudinal mechanical waves. Solid media can support
longitudinal and transverse sound waves. In this course, we will only
consider longitudinal sound waves and, for simplicity, we say sound waves
are longitudinal waves.
Sound waves are very important to us; without them we would not be able to communicate. The vibrations that
you produce in your mouth are carried by sound waves to your friends' ears. Human
ear can detect vibrations in the range of 20 to 2000 Hz. Sound waves,
also, are used in many applications. For example, ships use sound
waves to detect underwater obstacles and fishes. Vibrations with
frequencies higher than 20000 Hz are called ultrasound waves.
Ultrasound waves are used by doctors to image fetuses in his
mother's womb and they are used by engineers to detect defects in
structures. Vibrations with frequencies below 10 Hz, can travel over
very long distances and because of this they are used to probe Earth's crust, for example, for oil.
In this and the next two chapters we will study thermodynamics.
Thermodynamics is the study of the thermal energy. Thermodynamics is a very
important branch of science and engineering. For example, chemists
need it to optimize certain products of chemical reactions, chemical
engineers use thermodynamics in their designs of chemical plants, mechanical
engineers implement laws of thermodynamics to design effective engines and
refrigerators, and architects need to understand basic heat transfer
mechanism to insulate and save in cooling or heating buildings.