So, I am reading my Modern Physics textbook (Tipler & Llewellyn), in the chapter on relativity. In discussing the Michelson-Morley experiment, the book states, "The speed of the waves depends on the properties of the medium and is derived relative to the medium. For example, the speed of sound waves in air, i.e., their absolute motion relative to still air, can be measured." Some further examples and this statement suggest to me that the speed of a wave relative to the medium is dependent on the speed of the source relative to the medium. However, later in the book it states quite clearly, "the speed of sound waves does not depend on the motion of the sound source. When an approaching car sounds its horn...the speed of the waves traveling through the air does not depend on the speed of the car." Am I missing something here? Which statement is correct?