On this wave animation website, I noticed that on the section titled "From high to low speed (low density to high density)", there's an animation of a wave losing amplitude as it goes from a low density to high density region.
Why does the amplitude of the wave change because of the wave speed? I thought that wave speed/frequency/wavelength never changed amplitude, so this was really confusing to me.
I found another example of this here. I thought that increasing the volume of sound increases the amplitude of the sound, so I thought the answer was (A). However, the answer is (C), and somehow wave speed is also being changed by the volume.
These 2 examples make me think there's some relation between amplitude and wave speed, but I haven't found any resource/website that talks about a relationship between the two. Is there one?