For my IB Physics Extended Essay, I have just changed my topic from momentum to this and I have really little time of doing it..... (Due in Oct) My research question would be The effect of angular velocity of circular motion of a moving sound source on the sound frequency. I am planning to place an electric motor at the bottom and put a stick or ruler on top of the motor. Then, I would put a phone with a controlled sound frequency and a counter-weight on each end of the stick/ruler, a mic will be placed somewhere near the set up. The speed of the electric motor will be changed and see how it affects the sound frequency BUT there is only an AC electric motor in my school where the speed cannot be controlled (so the speed can't be changed). I have heard that the speed depends on the amount of voltage supplied to a DC electric motor, but is it possible for me to manipulate the speed to run this experiment? THANKS IN ADVANCE!!!!!!!!!!!!