Determine which of the following must change when pitch gets higher: amplitude or frequency or wavelength or intensity or speed of the sound waves?
Both frequency and wavelength will change.
We perceive an increase of frequency as the increased pitch that you described. As the frequency (pitch) increases, the wavelength becomes shorter according to the universal wave equation (
The speed of the wave will not change, as it is dependent only on the properties of the medium through which the wave is traveling (ex. Temperature or pressure of air, density of solid, salinity of water, ...)
The amplitude, or intensity, of the wave is perceived by our ears as the loudness (think "amplifier"). Although the amplitude of the wave does not increase with pitch, it is true that our ears detect different frequencies at different intensity levels - so it is possible that a high frequency sound may seem louder to our ears than a low frequency sound of the same amplitude.
This video has a good overview of the science, mathematics of sound, frequency, and pitch: