Listen to an Academic Talk

Narrator: Listen to part of a talk in an astronomy class.

Woman: You've probably noticed that the Moon always shows us the same face. The craters and dark patches you can see tonight are the same ones people saw a thousand years ago. A lot of people conclude from this that the Moon doesn't rotate at all. Actually, it does. It turns once on its axis in about twenty-seven days, which is exactly the time it takes to orbit Earth once. Because those two periods match, the same side always faces us. Astronomers call this tidal locking. Here's how it happens. Earth's gravity pulls slightly harder on the near side of the Moon than on the far side, so the Moon is stretched a little. Billions of years ago, when the Moon was spinning faster, that stretched shape was constantly being pulled out of line, and the friction gradually slowed the spin until it matched the orbit. And this isn't unusual. Most of the large moons in our solar system are tidally locked to their planets.

Narrator: Listen to part of a talk in an economics class.

Woman: When economists talk about cost, they don't just mean money. Let's take an example. Say you have a free ticket to a concert on Saturday night. Free, right? Well, not exactly. Suppose that on the same night, you could have worked a shift at your part-time job and earned eighty dollars. By going to the concert, you give up that eighty dollars. Economists call this the opportunity cost: the value of the best alternative you give up when you make a choice. Notice I said the best alternative, not all of them. Maybe you could also have studied or seen a movie, but you only count the single most valuable option you gave up. This idea explains a lot of behavior that seems strange at first. For example, people who earn very high hourly wages often pay someone else to clean their homes, even if they enjoy cleaning. Their time is simply too valuable to spend that way.

Narrator: Listen to part of a talk in a food science class.

Woman: Why does toast taste so different from bread? The answer is a group of chemical reactions called the Maillard reaction, named after the French chemist Louis-Camille Maillard, who described it in nineteen twelve. When foods that contain proteins and certain sugars are heated, amino acids from the proteins react with the sugars and produce hundreds of new compounds. These compounds create the brown color and the rich, roasted flavors we associate with bread crusts, grilled meat, and roasted coffee. Now, temperature is key. The reaction happens slowly at lower temperatures, but it really speeds up at around one hundred forty degrees Celsius. That's why boiled meat never turns brown. Water can't get hotter than one hundred degrees at normal pressure, so the surface of the meat never gets hot enough. By the way, people often confuse this with caramelization, but caramelization involves sugar alone. The Maillard reaction needs both sugars and amino acids.