boing.mp3 source=freesound.org, Creative Commons 0 license, modified by John B
boing.ogg source=freesound.org, Creative Commons 0 license, modified by John B
cheer.mp3 source=PhET author=Sam Reid
cheer.ogg source=PhET author=Sam Reid
ding.mp3 source=PhET author=John B
ding.ogg source=PhET author=John B
trumpet.mp3 source=PhET author=John B
trumpet.ogg source=PhET author=John B