Mr Kundt – a physicist – had an idea more than 150 years ago: He wanted to make invisible sound waves visible for us and thus show people that every sound is a vibration in the air. So he took a tube and filled it with cork dust, and then repeatedly sent sounds through it.
Look closely: Can you see how the sound has left a wave-like print in the sand and how the grains bounce? So a single sound has quite a lot of energy, right?
The following video shows you again exactly how this experiment with the “standing sound wave” in a glass tube works: