Which factor does not affect the speed of sound waves in a medium?

The speed of sound waves in a medium is influenced by various properties of that medium, specifically its density, stiffness, and temperature. Medium density refers to how compact the molecules of the medium are, while medium stiffness indicates how resistant the medium is to deformation when an external force is applied. The higher the stiffness, the faster sound waves can travel through it. Temperature also plays a significant role; as temperature increases, the energy of the molecules increases, and this can affect the speed of sound.

In contrast, ultrasound frequency does not affect the speed of sound waves within a given medium. The speed of sound is a characteristic property determined by the medium itself rather than the frequency of the waves traveling through it. While frequency can influence other aspects of ultrasound, such as resolution and penetration, it does not change how fast sound travels in a specific medium. Thus, the choice indicating ultrasound frequency as a factor that does not affect the speed of sound is accurate.