Standing Wave on String. Videos to Watch.

The animation is from the Wikipedia pages on Standing Waves

This first video shows how two sine waves moving in opposite directions add to give a standing wave form. You might want to pause it and look at what the curves are doing from one moment to the next. Watch it a couple of times.

 Bad music but it looks really good.

This next video shows what those standing waves look like on a string.

And this is a video (Chinese Language) of a standing wave on a spring.