熱膨張／What Happens When You Heat Metal

DENJIRO: Today, we'll see an interesting phenomenon using metal. We'll heat this metal plate. What will happen? GIRL: It's moving by itself! DENJIRO: Here's how it works. A bent piece of thin wire is placed under the metal plate, and a drawing of a rabbit is placed at the tip of the wire. When you heat metal, it expands. This expansion is what causes the wire to rotate and the drawing to move. The phenomenon of metal expanding due to heat is called thermal expansion. Let's now cool the metal plate. I'll place ice on it. GIRL: It's moving back! DENJIRO: Cooling the metal plate causes it to shrink, and make the wire roll in reverse. The rate of thermal expansion differs depending on the metal. Let's see how it is different between aluminum and iron. We'll heat these two metals and compare their thermal expansion rate. The expanding metal touching this block will trigger an electric current and make a drawing stand up. So, here we go. GIRL: The drawing for aluminum went up first! ON-SCREEN TEXT: Two minutes later. DENJIRO: The rate at which a metal expands due to heat is called the coefficient of thermal expansion. The value is different for each metal. For aluminum, it's 23, and 11 for iron. Aluminum expands well under heat, but iron doesn't expand so much. I hope energy will bring you all happiness. Our magic word is "Happy Energy!"