In the this video the person cuts 6 grooves on a wooden pencil and mounts a paper propeller using a pin on the soft eraser side.
As he starts rubbing the groves vigorously, the paper propeller starts spinning clockwise.
The mysterious thing is this: torque is generated on the paper from just translational motion (the rubbing of the grooves)! Where does this torque come from?! My current hypothesis is that the pencil traces a small circle if you hold it with your hand while rubbing the grooves, but I've disproved this theory when I mounted a replicated device on a clamp and performed the rubbing - the rotations still happens! I've ran computer simulations on this and have yet to determine the origins of the torque, which means the torque generation lies in non-ideality. An ideal system will dissipate the vibrational energy perfectly, generating no torque.
How can sound waves in a wooden media generate any torque as it leaves through a pivoted rigid body (the paper propeller)?
Can anyone shed some insights to a theory of how this motor works, and provide quantative/numerical solutions to this problem?
A numerical solution that quantizes all relevant parameters would be extremely helpful to explain this mysterious phenomena!
P.S. IMPT: Please provide numerical solutions to back your theory up! Please do not just provide qualitative solutions!
My current sentiments: It has something to do with acoustics which may tell us the efficiency of energy transfer to propeller and an non-ideality which generates torque, however the latter mechanism of origin of the torque remains shrouded in mystery.