### Fermi Problem Friday: Back to School Edition

There's nothing like a crisp fall day—fresh, cool air, leaves crunching underfoot, an apple in your hand, and ten pounds of textbooks in your backpack slowly giving you scoliosis as you haul them around campus. In the spirit of back-to-school, join me in imagining the following scenario.

You get to your class on time for once, file inside with your classmates, and find a seat. Then the teacher starts talking. And talking. And talking. Time dilation seems to be at work. You check your watch—still another half hour to go. And you're starting to feel not very good. Must be this droning professor, you think. You tug at your collar and cough; your head starts to hurt. Your eyes wander to the door and you wonder whether it's been shut this whole time. Then it dawns on you...

The Fermi Problem:

Assuming you're not in a big lecture hall and the professor shuts the door at the start of class, how long does it take for you and your classmates to deplete the oxygen enough to feel it? If you're in school, try using the classroom dimensions and number of students from one of your classes. (That's a hint on where to start.) Stay tuned for the answer on Monday's blog—it might surprise you.

### 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?