Links for 2010-04-08

The two waves cancel each other out, leaving a completely unmoving string due to destructive interference. My student asked me: what happens to the energy? As posed, it seems that we started with two waves carrying energy, but they canceled each other out, leaving no energy! This interpretation cannot possibly be correct, so where is the flaw in our description?

There are actually two aspects to the answer that I want to address, each of which is rather important in the understanding of wave phenomena. The first of these is the observation that the answer to the question depends on how the waves were generated in the first place!

"Tonight we have din-dins in Hell!"

"Over the last several years, the Internet has evolved from being a distraction to something that feels more sinister. Even when I am away from the computer I am aware that I AM AWAY FROM MY COMPUTER and am scheming about how to GET BACK ON THE COMPUTER. I've tried various strategies to limit my time online: leaving my laptop at my studio when I go home, leaving it at home when I go to my studio, a Saturday moratorium on usage. But nothing has worked for long. More and more hours of my life evaporate in front of YouTube. Supposedly addiction isn't a moral failing, but it feels as if it is."

How floating an aluminum disk on the surface of a glass of water is different than floating a boat.