https://www.youtube.com/watch?v=HvklXnAAoHA
https://www.ducksters.com/science/physics/waves.php
https://www.youtube.com/watch?v=9M6eWK4VG1g
https://www.youtube.com/watch?v=_LRc6k-clzE
Frequency:
https://www.ducksters.com/science/physics/properties_of_waves.php
www.generationgenius.com/?share=E5EFF
