### String Theory (No, not that kind!)

Creating a slow-motion effect in real life takes some creativity, but with the help of a few strobe lights and a frequency generator, the folks at Pasco put together one that’s truly mesmerizing, on top of being educational. Watch the video of it below, and then read on to find out how it’s done!

The lights illuminating the string from below are hooked up to a frequency generator, which turns them on and off several times per second, much faster than the human eye can see. The string is also vibrating up and down at a similar rate, leading to the two-node standing wave that shows up on film as a blur.
Imagine the strobe lights and the string’s vibrations being perfectly in sync, so that the string is in the same position every time the light flashes; the luminous string would appear to stand completely still. When the lights flash just slightly faster than the string’s vibration frequency, the string doesn’t have time to make it all the way back to its previous position before the lights flash again, so the wave appears to have shifted the next time it lights up; the same effect can also be created with a strobe rate slightly slower than the string’s frequency. By keeping the rates very close to one another, the apparatus creates the effect shown above, where the illuminated string oscillates up and down at a rate depending only on the difference between two frequencies. This is actually somewhat similar to the phenomenon of acoustic beats, the odd volume fluctuations you hear when two musicians playing the same note are just slightly out of tune with one another.
Check back soon for more cool demo stuff from the 2015 American Association of Physics Teachers Summer meeting, where we found this awesome science display! (And if you know any "string theory" jokes, let us hear 'em in the comments)

1. OK! I am here proposing my new theory:
Rubber Theory
Sponge Theory
Spring Theory
Glue Theory
Drum Theory
etc
��puff proposing

### How 4,000 Physicists Gave a Vegas Casino its Worst Week Ever

What happens when several thousand distinguished physicists, researchers, and students descend on the nation’s gambling capital for a conference? The answer is "a bad week for the casino"—but you'd never guess why.

### Ask a Physicist: Phone Flash Sharpie Shock!

Lexie and Xavier, from Orlando, FL want to know: "What's going on in this video ? Our science teacher claims that the pain comes from a small electrical shock, but we believe that this is due to the absorption of light. Please help us resolve this dispute!"

### The Science of Ice Cream: Part One

Even though it's been a warm couple of months already, it's officially summer. A delicious, science-filled way to beat the heat? Making homemade ice cream. (We've since updated this article to include the science behind vegan ice cream. To learn more about ice cream science, check out The Science of Ice Cream, Redux ) Image Credit: St0rmz via Flickr Over at Physics@Home there's an easy recipe for homemade ice cream. But what kind of milk should you use to make ice cream? And do you really need to chill the ice cream base before making it? Why do ice cream recipes always call for salt on ice?