Then when he tries to grab some of the oobleck, it pours through his fingers like a liquid once again. In a bowl it looks like a liquid, but when Kung punches the bowl, it feels solid on his fist. This causes oobleck to exhibit some of the properties of both solids in liquids. The Quick Conundrum for today involves something called "oobleck." Oobleck is just a mixture of corn starch and water, but the starch isn't completely dissolved in the water. ![]() My written description of this Rolling Spool Paradox won't do it justice, so let me provide a link where you can see what's going on: ![]() Basically, depending on which way you pull on the thread, it's possible to make the spool move forwards or backwards. His final paradox involves a spool of string. He adds that the idea that information takes time to transmit will show up in his later lectures. He says that it's as if information - namely, the fact that the Slinky has been cut - takes time for it to arrive at the bottom of the Slinky. The two opposing forces, gravity and the recoil, balance out exactly, so the bottom continues to float in the air until the top finishes recoiling as it falls - only then will the bottom of the Slinky fall to the ground. Well, when Kung cuts the Slinky, the bottom actually does neither. Then he asks, what would happen to the bottom of the Slinky if he were to detach the toy from the ceiling? It could be that gravity will cause the bottom to descend, but it could also be that the Slinky will recoil, thereby causing the bottom to ascend. He hangs a toy from the ceiling, which causes gravity to stretch it out a little. Next, Kung moves on to some paradoxes involving springs, but he demonstrates these by using a very large spring - also known as a Slinky. You simply take a large tank the same shape as the ship, pour in the gallon of water, and then add the ship. ![]() Kung begins the lecture by describing how to float a ship in one gallon of water. Lecture 15 of David Kung's Mind-Bending Math is called "Enigmas of Everyday Objects." I've heard of many of these mathematical paradoxes before, but actually, most of the paradoxes Dave Kung describes in this lecture pertain more to physics and are new to me.
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