Description With the help of the robot and the aforementioned materials, we were able to demonstrate the Doppler effect. Initially we conducted various tests regarding the movement of the robot through the “blocky” software provided by the “Sapienza” University of Rome. After stabilizing the programme that defines the robot’s movements:
begin() setSpeed(0.2,0,0.5,False) setSpeed(4,0,0.8,False) setSpeed(0.4,0,0.2,False) setSpeed(0.3,0,0.1,False) setSpeed(0.2,0,0.1,False) setSpeed(0.1,0,0.1,False) setSpeed(0,0,3,False) setSpeed((-0.2),0,0.5,False) setSpeed((-4),0,0.8,False) setSpeed((-0.4),0,0.5,False) end()
We mounted on the front of the robot a microphone, connected to the oscilloscope. Apart from the microphone, we connected to the oscilloscope a function generator, syntonized on the same frequency of the source, which in our case was the speaker connected to the phone. The phone’s purpose was to generate a frequency set through the application “Function Generator”. The frequency needed to be set must respect the range of the human voice’s frequencies (the frequencies’ interval dipends from the specs of the microphone). The oscilloscope presents on the X and Y axes the signal that receives from both the frequency generator and the microphone. When both signals have the same frequency but are 90 degrees out of phase, the composition represented by the oscilloscope, forms a circle. When the frequency perceived by the microphone changes, the image tends to deform into an ellipse. If the difference between the two registered frequencies changes widely, the shapes represented by the oscilloscope will become more and more irregular. These shapes are called “shapes of Lissajous” and by exploiting this phenomenon, they will allow us to highlight even a minimal change of the perceived frequency. At this point we have passed on the practical demonstration of the experiment. We make the speakers reproduce a definite frequency that we syntonize with the frequency generator. The robot, by moving back and forth in a strait line, will move the microphone, which as a consequence of the Doppler effect will register different frequencies during its movement. This will result in a variation of the shape represented by the oscilloscope, that proves our hypothesis. By repeating the experience more than once, it results that the most efficient frequency to verify the experiment is around 10KHz.