Acoustic Radiometer

Demonstration of an Acoustic Radiometer -- original video recording by Timothy G. Simmons, National Center for Physical Acoustics, University of Mississippi (1998). 



This is a digital transfer from an old VHS video tape that I found in my office.  I had seen this acoustic radiometer demonstrated at a meeting of the Acoustical Society of America sometime around 1996-1997. I am posting it here to preserve it.



A simplified (not completely correct) explanation of how it works: A sound field is generated in the plexiglass chamber by the speakers in the back.  The radiometer is balanced on a pin, and each "panel" has one side with absorbing material (darker), and the other side with reflecting material (silver).  When the box is closed and the sound is turned on, the spindle rotates as if it is being "pushed" by a net force acting on the reflecting side of the panels. This would imply a conservation of momentum resulting from radiation pressure from the sound -- a reflection of the sound wave results in more momentum transferred to the reflective panel than is delivered to the absorbing side.