WEBVTT 00:00:05.684 --> 00:00:08.684 French fries are delicious. 00:00:08.684 --> 00:00:12.684 French fries with ketchup are a little slice of heaven. 00:00:12.684 --> 00:00:14.432 The problem is it's basically impossible 00:00:14.432 --> 00:00:16.463 to pour the exactly right amount. 00:00:16.463 --> 00:00:19.768 We're so used to pouring ketchup that we don't realize 00:00:19.768 --> 00:00:21.851 how weird its behavior is. 00:00:21.851 --> 00:00:26.430 Imagine a ketchup bottle filled with a straight up solid like steel. 00:00:26.430 --> 00:00:29.475 No amount of shaking would ever get the steel out. 00:00:29.475 --> 00:00:32.395 Now imagine that same bottle full of a liquid like water. 00:00:32.395 --> 00:00:34.434 That would pour like a dream. 00:00:34.434 --> 00:00:36.851 Ketchup, though, can't seem to make up its mind. 00:00:36.851 --> 00:00:38.933 Is it is a solid? Or a liquid? 00:00:38.933 --> 00:00:41.654 The answer is, it depends. 00:00:41.654 --> 00:00:44.846 The world's most common fluids like water, oils and alcohols 00:00:44.846 --> 00:00:47.597 respond to force linearly. 00:00:47.597 --> 00:00:51.238 If you push on them twice as hard, they move twice as fast. 00:00:51.238 --> 00:00:54.355 Sir Isaac Newton, of apple fame, first proposed this relationship, 00:00:54.355 --> 00:00:57.739 and so those fluids are called Newtonian fluids. 00:00:57.739 --> 00:01:00.695 Ketchup, though, is part of a merry band of linear rule breakers 00:01:00.695 --> 00:01:03.286 called Non-Newtonian fluids. 00:01:03.286 --> 00:01:06.368 Mayonnaise, toothpaste, blood, paint, peanut butter 00:01:06.368 --> 00:01:09.870 and lots of other fluids respond to force non-linearly. 00:01:09.870 --> 00:01:11.915 That is, their apparent thickness changes 00:01:11.915 --> 00:01:15.336 depending on how hard you push, or how long, or how fast. 00:01:15.336 --> 00:01:18.551 And ketchup is actually Non-Newtonian in two different ways. 00:01:18.551 --> 00:01:22.849 Way number one: the harder you push, the thinner ketchup seems to get. 00:01:22.849 --> 00:01:24.715 Below a certain pushing force, 00:01:24.715 --> 00:01:26.717 ketchup basically behaves like a solid. 00:01:26.717 --> 00:01:29.134 But once you pass that breaking point, 00:01:29.134 --> 00:01:33.384 it switches gears and becomes a thousand times thinner than it was before. 00:01:33.384 --> 00:01:35.384 Sound familiar right? 00:01:35.384 --> 00:01:39.276 Way number two: if you push with a force below the threshold force 00:01:39.276 --> 00:01:41.569 eventually, the ketchup will start to flow. 00:01:41.569 --> 00:01:45.158 In this case, time, not force, is the key to releasing ketchup 00:01:45.158 --> 00:01:46.992 from its glassy prison. 00:01:46.992 --> 00:01:49.620 Alright, so, why does ketchup act all weird? 00:01:49.620 --> 00:01:52.634 Well, it's made from tomatoes, pulverized, smashed, thrashed, 00:01:52.634 --> 00:01:55.457 utterly destroyed tomatoes. 00:01:55.457 --> 00:01:56.801 See these tiny particles? 00:01:56.801 --> 00:01:58.586 This is what remains of tomatoes cells 00:01:58.586 --> 00:02:01.215 after they go through the ketchup treatment. 00:02:01.215 --> 00:02:02.925 And the liquid around those particles? 00:02:02.925 --> 00:02:05.967 That's mostly water and some vinegar, sugar, and spices. 00:02:05.967 --> 00:02:08.190 When ketchup is just sitting around, 00:02:08.190 --> 00:02:11.551 the tomato particles are evenly and randomly distributed. 00:02:11.551 --> 00:02:13.967 Now, let's say you apply a weak force very quickly. 00:02:13.967 --> 00:02:15.522 The particles bump into each other, 00:02:15.522 --> 00:02:17.218 but can't get out of each other's way, 00:02:17.218 --> 00:02:18.717 so the ketchup doesn't flow. 00:02:18.717 --> 00:02:21.777 Now, let's say you apply a strong force very quickly. 00:02:21.777 --> 00:02:24.613 That extra force is enough to squish the tomato particles, 00:02:24.613 --> 00:02:25.945 so maybe instead of little spheres, 00:02:25.945 --> 00:02:28.827 they get smushed into little ellipses, and boom! 00:02:28.827 --> 00:02:30.784 Now you have enough space for one group of particles 00:02:30.784 --> 00:02:33.633 to get passed others and the ketchup flows. 00:02:33.633 --> 00:02:37.716 Now let's say you apply a very weak force but for a very long time. 00:02:37.716 --> 00:02:41.253 Turns out, we're not exactly sure what happens in this scenario. 00:02:41.253 --> 00:02:45.009 One possibility is that the tomato particles near the walls of the container 00:02:45.009 --> 00:02:47.299 slowly get bumped towards the middle, 00:02:47.299 --> 00:02:48.800 leaving the soup they were dissolved in, 00:02:48.800 --> 00:02:50.383 which remember is basically water, 00:02:50.383 --> 00:02:51.884 near the edges. 00:02:51.884 --> 00:02:54.383 That water serves as a lubricant betwen the glass bottle 00:02:54.383 --> 00:02:56.436 and the center plug of ketchup, 00:02:56.436 --> 00:02:58.551 and so the ketchup flows. 00:02:58.551 --> 00:03:01.941 Another possibility is that the particles slowly rearrange themselves 00:03:01.941 --> 00:03:05.801 into lots of small groups, which then flow past each other. 00:03:05.801 --> 00:03:08.133 Scientists who study fluid flows are still actively researching 00:03:08.133 --> 00:03:11.326 how ketchup and its merry friends work. 00:03:11.326 --> 00:03:13.411 Ketchup basically gets thinner the harder you push, 00:03:13.411 --> 00:03:16.498 but other substances, like oobleck or some natural peanut butters, 00:03:16.498 --> 00:03:19.301 actually get thicker the harder you push. 00:03:19.301 --> 00:03:21.717 Others can climb up rotating rods, 00:03:21.717 --> 00:03:24.090 or continue to pour themselves out of a beeker, 00:03:24.090 --> 00:03:26.012 once you get them started. 00:03:26.012 --> 00:03:27.384 From a physics perspective, though, 00:03:27.384 --> 00:03:30.217 ketchup is one of the more complicated mixtures out there. 00:03:30.217 --> 00:03:32.467 And as if that weren't enough, the balance of ingredients 00:03:32.467 --> 00:03:35.300 and the presence of natural thickeners like xanthan gum, 00:03:35.300 --> 00:03:37.934 which is also found in many fruit drinks and milkshakes, 00:03:37.934 --> 00:03:39.605 can mean that two different ketchups 00:03:39.605 --> 00:03:41.549 can behave completely differently. 00:03:41.549 --> 00:03:44.234 But most will show two telltale properties: 00:03:44.234 --> 00:03:46.069 sudden thinning at a threshold force, 00:03:46.069 --> 00:03:48.321 and more gradual thinning after a small force 00:03:48.321 --> 00:03:50.365 is applied for a long time. 00:03:50.365 --> 00:03:53.327 And that means you could get ketchup out of the bottle in two ways: 00:03:53.327 --> 00:03:55.966 either give it a series of long, slow languid shakes 00:03:55.966 --> 00:03:58.467 making sure you don't ever stop applying force, 00:03:58.467 --> 00:04:02.504 or you could hit the bottle once very, very hard. 00:04:02.504 --> 00:04:04.717 What the real pros do is keep the lid on, 00:04:04.717 --> 00:04:07.132 give the bottle a few short, sharp shakes 00:04:07.132 --> 00:04:08.550 to wake up all those tomato particles, 00:04:08.550 --> 00:04:10.428 and then take the lid off 00:04:10.428 --> 00:04:13.801 and do a nice controlled pour onto their heavenly fries.