https://phet.colorado.edu/sims/html/wave-on-a-string/latest/wave-on-a-string_en.html
# g-85175279@moe-dl.edu.my
# https://sites.google.com/moe-dl.edu.my/fizik-on9
# https://sites.google.com/moe-dl.edu.my/sains-on9