Why is ketchup so hard to pour? - George Zaidan
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0:06 - 0:09French fries are delicious.
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0:09 - 0:13French fries with ketchup are a little slice of heaven.
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0:13 - 0:14The problem is it's basically impossible
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0:14 - 0:16to pour the exactly right amount.
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0:16 - 0:20We're so used to pouring ketchup that we don't realize
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0:20 - 0:22how weird its behavior is.
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0:22 - 0:26Imagine a ketchup bottle filled with a straight up solid like steel.
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0:26 - 0:29No amount of shaking would ever get the steel out.
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0:29 - 0:32Now imagine that same bottle full of a liquid like water.
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0:32 - 0:34That would pour like a dream.
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0:34 - 0:37Ketchup, though, can't seem to make up its mind.
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0:37 - 0:39Is it is a solid? Or a liquid?
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0:39 - 0:42The answer is, it depends.
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0:42 - 0:45The world's most common fluids like water, oils and alcohols
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0:45 - 0:48respond to force linearly.
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0:48 - 0:51If you push on them twice as hard, they move twice as fast.
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0:51 - 0:54Sir Isaac Newton, of apple fame, first proposed this relationship,
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0:54 - 0:58and so those fluids are called Newtonian fluids.
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0:58 - 1:01Ketchup, though, is part of a merry band of linear rule breakers
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1:01 - 1:03called Non-Newtonian fluids.
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1:03 - 1:06Mayonnaise, toothpaste, blood, paint, peanut butter
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1:06 - 1:10and lots of other fluids respond to force non-linearly.
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1:10 - 1:12That is, their apparent thickness changes
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1:12 - 1:15depending on how hard you push, or how long, or how fast.
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1:15 - 1:19And ketchup is actually Non-Newtonian in two different ways.
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1:19 - 1:23Way number one: the harder you push, the thinner ketchup seems to get.
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1:23 - 1:25Below a certain pushing force,
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1:25 - 1:27ketchup basically behaves like a solid.
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1:27 - 1:29But once you pass that breaking point,
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1:29 - 1:33it switches gears and becomes a thousand times thinner than it was before.
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1:33 - 1:35Sound familiar right?
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1:35 - 1:39Way number two: if you push with a force below the threshold force
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1:39 - 1:42eventually, the ketchup will start to flow.
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1:42 - 1:45In this case, time, not force, is the key to releasing ketchup
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1:45 - 1:47from its glassy prison.
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1:47 - 1:50Alright, so, why does ketchup act all weird?
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1:50 - 1:53Well, it's made from tomatoes, pulverized, smashed, thrashed,
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1:53 - 1:55utterly destroyed tomatoes.
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1:55 - 1:57See these tiny particles?
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1:57 - 1:59This is what remains of tomatoes cells
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1:59 - 2:01after they go through the ketchup treatment.
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2:01 - 2:03And the liquid around those particles?
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2:03 - 2:06That's mostly water and some vinegar, sugar, and spices.
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2:06 - 2:08When ketchup is just sitting around,
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2:08 - 2:12the tomato particles are evenly and randomly distributed.
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2:12 - 2:14Now, let's say you apply a weak force very quickly.
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2:14 - 2:16The particles bump into each other,
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2:16 - 2:17but can't get out of each other's way,
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2:17 - 2:19so the ketchup doesn't flow.
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2:19 - 2:22Now, let's say you apply a strong force very quickly.
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2:22 - 2:25That extra force is enough to squish the tomato particles,
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2:25 - 2:26so maybe instead of little spheres,
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2:26 - 2:29they get smushed into little ellipses, and boom!
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2:29 - 2:31Now you have enough space for one group of particles
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2:31 - 2:34to get passed others and the ketchup flows.
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2:34 - 2:38Now let's say you apply a very weak force but for a very long time.
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2:38 - 2:41Turns out, we're not exactly sure what happens in this scenario.
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2:41 - 2:45One possibility is that the tomato particles near the walls of the container
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2:45 - 2:47slowly get bumped towards the middle,
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2:47 - 2:49leaving the soup they were dissolved in,
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2:49 - 2:50which remember is basically water,
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2:50 - 2:52near the edges.
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2:52 - 2:54That water serves as a lubricant betwen the glass bottle
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2:54 - 2:56and the center plug of ketchup,
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2:56 - 2:59and so the ketchup flows.
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2:59 - 3:02Another possibility is that the particles slowly rearrange themselves
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3:02 - 3:06into lots of small groups, which then flow past each other.
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3:06 - 3:08Scientists who study fluid flows are still actively researching
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3:08 - 3:11how ketchup and its merry friends work.
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3:11 - 3:13Ketchup basically gets thinner the harder you push,
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3:13 - 3:16but other substances, like oobleck or some natural peanut butters,
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3:16 - 3:19actually get thicker the harder you push.
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3:19 - 3:22Others can climb up rotating rods,
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3:22 - 3:24or continue to pour themselves out of a beeker,
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3:24 - 3:26once you get them started.
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3:26 - 3:27From a physics perspective, though,
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3:27 - 3:30ketchup is one of the more complicated mixtures out there.
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3:30 - 3:32And as if that weren't enough, the balance of ingredients
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3:32 - 3:35and the presence of natural thickeners like xanthan gum,
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3:35 - 3:38which is also found in many fruit drinks and milkshakes,
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3:38 - 3:40can mean that two different ketchups
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3:40 - 3:42can behave completely differently.
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3:42 - 3:44But most will show two telltale properties:
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3:44 - 3:46sudden thinning at a threshold force,
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3:46 - 3:48and more gradual thinning after a small force
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3:48 - 3:50is applied for a long time.
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3:50 - 3:53And that means you could get ketchup out of the bottle in two ways:
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3:53 - 3:56either give it a series of long, slow languid shakes
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3:56 - 3:58making sure you don't ever stop applying force,
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3:58 - 4:03or you could hit the bottle once very, very hard.
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4:03 - 4:05What the real pros do is keep the lid on,
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4:05 - 4:07give the bottle a few short, sharp shakes
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4:07 - 4:09to wake up all those tomato particles,
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4:09 - 4:10and then take the lid off
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4:10 - 4:14and do a nice controlled pour onto their heavenly fries.
- Title:
- Why is ketchup so hard to pour? - George Zaidan
- Speaker:
- George Zaidan
- Description:
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View full lesson: http://ed.ted.com/lessons/why-is-ketchup-so-hard-to-pour-george-zaidan
Ever go to pour ketchup on your fries...and nothing comes out? Or the opposite happens, and your plate is suddenly swimming in a sea of red? George Zaidan describes the physics behind this frustrating phenomenon, explaining how ketchup and other non-Newtonian fluids can suddenly transition from solid to liquid and back again.
Lesson by George Zaidan, animation by TOGETHER.
- Video Language:
- English
- Team:
- closed TED
- Project:
- TED-Ed
- Duration:
- 04:29
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Retired user
a typo / mistake in the below line
3:22 - 3:24
or continue to pour themselves out of a BEAKER