The demos show waves on a string, but we can draw direct analogies to EM waves.
From high speed to low speed (low density to high density)
From low speed to high speed (high density to low density)
Also, here’s a great video!
Big Think is an online forum founded in 2007 by former staff members on the Charlie Rose show. It primarily features interviews and has been described as a YouTube for ideas. My initial perusal gives me the impression this is better than TED.