Frenette Friction Heater This is too easy.    

It is easier than it looks.  Briefly: You spin one can inside a larger can with some cooking oil in it and it will produce heat.  Frenette states in his patent that the spacing at the bottom should not be more than 1/4 inch. The spacing on the sides should not exceed 1/8 inch. This close tolerance is what creates the friction. Frenette cautions that the oil should not exceed 1/3 of the bottom of the can because of expansion. The use of the Adams motor is only a recommendation because of it's speed and efficiency although any motor can be used.

Tested: I did try this heater but my cans were not with tolerance so I did not get the heat for the amount of work.  I wanted to get better suited cans before I try it again. There is practically no friction with this device.