Kaplan Nursing Entrance Practice Exam

Which characteristic is true of mechanical waves, including sound waves?

1. They can travel through a vacuum without any medium

2. They are affected by the medium's density

3. They can only travel through liquids

4. They can travel at the speed of light

The correct answer is: They are affected by the medium's density

Mechanical waves, including sound waves, are defined by their need for a medium through which to travel. This characteristic is directly related to the behavior of these waves in various mediums. When sound waves travel through different materials—such as gases, liquids, or solids—their speed and efficiency of propagation are significantly impacted by the properties of the medium, particularly its density. For instance, sound travels more slowly in air than in water or steel because the density and elasticity of these materials differ. Higher density typically facilitates faster transmission of sound waves as the particles in closer proximity can transmit the vibrational energy more efficiently. In contrast, sound waves cannot travel through a vacuum because there are no particles present to carry the sound vibrations. This is the fundamental reason why sound does not propagate in outer space. Additionally, while sound waves can travel through solids and liquids, they do not have the capability to travel solely through liquids or reach the speed of light like electromagnetic waves do. Thus, the assertion about being influenced by the medium's density accurately captures a key aspect of mechanical waves.