Two great physics by Michael Schick. The first is 20 minutes of physics. The second covers basic physics, knobology and artefacts, all in 16 minutes
If you prefer having something to read rather than watching videos, this is 14-page publication provides an excellent overview of basic ultrasound physics as well some more advanced concepts. If you’re starting from scratch...
The first 20 minutes of this video are dedicated to a basic introduction to ultrasound physics. It also includes some detail of probe manipulation.
An excellent 35 minute summary of ultrasound physics from Mike and Matt.
Physics and Technical Facts for the Beginner is a brief overview of basic ultrasound physics. It include some excellent descriptions of artefacts.