Pitch relates to the physics principle of frequency. The higher the frequency, the higher the pitch. The lower the frequency, the higher the frequency. To generate higher frequencies, there must be higher vibrations. As pitch is frequency, it is measured in the unit of Hz or cycles per second.
“Mandy, you can remember higher frequencies require more vibration, because kids who make squeaky noises do so because they are more energetic; but old folk who moan do so because they are… less energetic.”