Animated sine wave addition

My son is studying physics at school and one of topics was "waves". The physics study book he is using is printed and so doesn't include any wave animations. I thought animations would help with understanding but couldn't find any on-line animation where the user could change the wave frequency, phase.

I've wrote a WPF application where the user could control the frequency, phase of two sine wave and see the result of adding these two wave together. I then ported this to silverlight (which required a few small changes to the code) and published the result on www.nzdev.com

Since then, I've added the ability to also change the wave amplitude.