Infrasound and ultrasound
Physics Narrative for 11-14
Explaining the terms infrasound and ultrasound, used for vibrations that we cannot hear
Our ears can detect only a relatively small range of frequencies of vibration. Beyond what we can hear there is:
- Infrasound, where the rate of vibration is too low for us to hear
- Ultrasound, where the rate of vibration is too high for us to hear
This full range of frequencies of vibration, from a few vibrations per second to many vibrations per second, is called a spectrum. Just as there is the electromagnetic spectrum of light (complete with infrared, the visible region, and ultraviolet) so too there is the spectrum of sound.
There is more about frequency in episode 02.
Sounds heard by humans and other organisms
Not all organisms are sensitive to the same range of vibrations. That's why some dog whistles are inaudible – to us.
These are approximate values. You cannot just ask a ferret if he can hear a particular sound. Nor are the organisms equally sensitive to sound over the whole range of their hearing.