Speed of sound
https://app.pivotinteractives.com/activities/5a749158fa9eab001ad4b585/preview
See varying E and B fields
See photons heating ground/air
http://mw.concord.org/nextgen/#interactives/physics/light-sound-physics/sunlight-infrared-physics
See varying E and B fields
http://www.walter-fendt.de/html5/phen/electromagneticwave_en.htm
Reflection and refraction
http://www.walter-fendt.de/html5/phen/refractionhuygens_en.htm
Resonance
Seismic waves
Law of Moments
Balance the beam with different masses
http://www.physicsclassroom.com/Physics-Interactives/Balance-and-Rotation/Balance-Beam