French fries are delicious. French fries with ketchup are a little slice of heaven. The problem is it's basically impossible to pour the exactly right amount. We're so used to pouring ketchup that we don't realize how weird its behavior is. Imagine a ketchup bottle filled with a straight up solid like steel. No amount of shaking would ever get the steel out. Now imagine that same bottle full of a liquid like water. That would pour like a dream. Ketchup, though, can't seem to make up its mind. Is it is a solid? Or a liquid? The answer is, it depends. The world's most common fluids like water, oils and alcohols respond to force linearly. If you push on them twice as hard, they move twice as fast. Sir Isaac Newton, of apple fame, first proposed this relationship, and so those fluids are called Newtonian fluids. Ketchup, though, is part of a merry band of linear rule breakers called Non-Newtonian fluids. Mayonnaise, toothpaste, blood, paint, peanut butter and lots of other fluids respond to force non-linearly. That is, their apparent thickness changes depending on how hard you push, or how long, or how fast. And ketchup is actually Non-Newtonian in two different ways. Way number one: the harder you push, the thinner ketchup seems to get. Below a certain pushing force, ketchup basically behaves like a solid. But once you pass that breaking point, it switches gears and becomes a thousand times thinner than it was before. Sound familiar right? Way number two: if you push with a force below the threshold force eventually, the ketchup will start to flow. In this case, time, not force, is the key to releasing ketchup from its glassy prison. Alright, so, why does ketchup act all weird? Well, it's made from tomatoes, pulverized, smashed, thrashed, utterly destroyed tomatoes. See these tiny particles? This is what remains of tomatoes cells after they go through the ketchup treatment. And the liquid around those particles? That's mostly water and some vinegar, sugar, and spices. When ketchup is just sitting around, the tomato particles are evenly and randomly distributed. Now, let's say you apply a weak force very quickly. The particles bump into each other, but can't get out of each other's way, so the ketchup doesn't flow. Now, let's say you apply a strong force very quickly. That extra force is enough to squish the tomato particles, so maybe instead of little spheres, they get smushed into little ellipses, and boom! Now you have enough space for one group of particles to get passed others and the ketchup flows. Now let's say you apply a very weak force but for a very long time. Turns out, we're not exactly sure what happens in this scenario. One possibility is that the tomato particles near the walls of the container slowly get bumped towards the middle, leaving the soup they were dissolved in, which remember is basically water, near the edges. That water serves as a lubricant betwen the glass bottle and the center plug of ketchup, and so the ketchup flows. Another possibility is that the particles slowly rearrange themselves into lots of small groups, which then flow past each other. Scientists who study fluid flows are still actively researching how ketchup and its merry friends work. Ketchup basically gets thinner the harder you push, but other substances, like oobleck or some natural peanut butters, actually get thicker the harder you push. Others can climb up rotating rods, or continue to pour themselves out of a beeker, once you get them started. From a physics perspective, though, ketchup is one of the more complicated mixtures out there. And as if that weren't enough, the balance of ingredients and the presence of natural thickeners like xanthan gum, which is also found in many fruit drinks and milkshakes, can mean that two different ketchups can behave completely differently. But most will show two telltale properties: sudden thinning at a threshold force, and more gradual thinning after a small force is applied for a long time. And that means you could get ketchup out of the bottle in two ways: either give it a series of long, slow languid shakes making sure you don't ever stop applying force, or you could hit the bottle once very, very hard. What the real pros do is keep the lid on, give the bottle a few short, sharp shakes to wake up all those tomato particles, and then take the lid off and do a nice controlled pour onto their heavenly fries.
薯條是美味的。 加上番茄醬的薯條 感覺就像天堂一樣。 問題是基本上不可能 擠出確切數量的番茄醬。 我們習慣去使用番茄醬, 但是我們並沒有意識到 這是一個奇怪的現象。 想像裝滿了像鐵一樣固體的 番茄醬的瓶子。 即使再大的晃動 也不能把鐵倒出來。 現在想像瓶子裏裝滿了水。 便能輕易地倒出來。 儘管番茄醬自己 好像還沒下定決心, 它是固體?或者說是液體? 答案是,它取決于其他因素。 世界上最常見的流質 像是水、油以及酒精 對力大小的比例是成線性關係, 如果你用兩倍的力去擠壓, 便會以兩倍地速度被擠出來。 艾薩克·牛頓爵士,因蘋果而出名的那個, 首次提出這種關係, 所以這些液體也稱之為牛頓流體。 儘管番茄醬是一部分 打破這個線性規律定理的液體, 稱之為非牛頓流體。 蛋黃醬、牙膏、血液、油彩、花生醬 以及其它一些液體 對力大小都是非線性地。 這就是說,表面厚度的改變 取決于你擠壓時候用的力的 大小、時間長短,或者多快。 番茄醬從兩個角度 表現出非牛頓流體。 第一種:你用勁越大, 擠出來的似乎越少。 在一個確定的力大小之下, 番茄醬的特性就像鐵一樣。 但是如果你超過了那個臨界點, 它的流體特性大概會 比以前明顯一千倍。 是不是有種熟悉的感覺? 第二種:如果你使用臨界值之下的力, 最後,番茄醬的量便會開始下降。 這種情況下,時間,而不是力, 才是番茄醬的決定因素, 從這個光滑的容器中擠出。 好吧,為甚麼番茄醬的行為是如此奇怪? 用番茄碾碎,搗爛,捶打 而做出的番茄醬, 完全摧毀了番茄本來的樣子。 看到這些小東西了沒? 這個番茄遺的細胞 經過了一系列處理之後。 這些小東西周圍的液體是什麼? 大部份都是水以及一些醋、糖和香料。 當番茄醬放在一邊的時候, 這些番茄地小分子是平等地,被隨機打亂了。 現在,我們快速地用一個很小的力。 這些微粒相互碰撞, 但並無法擺脫其他, 所以番茄醬無法像液體一樣流動。 現在,讓我們快速地用一個極大的力, 這樣的一個力足夠擠壓這些番茄微粒, 所以可能就不再是小球, 它們被搗成小橢圓,然後嘣! 現在你有足夠的空間讓一小群微粒 穿過然後讓番茄醬流出。 現在讓我們用一個很小的力 但是作用很長的一個時間。 然後你會發現, 我們並不確定這裡發生了什麼。 一種可能性是靠近杯壁的番茄微粒 慢慢地被擠到了中間, 離開它們之前 溶解於其中的溶液, 而那個溶液 基本上就是水, 在邊緣地方的水。 水作為玻璃瓶 以及番茄醬中間的 一種潤滑劑, 然後番茄醬便可以流出來。 另一種可能是這些分子慢慢的重組 變成許多小組,接著它們便可以流出來。 研究流體的科學家仍然在研究 番茄醬和其它的果醬朋友 是如何工作的。 基本上番茄醬會隨著你力的變大而液化, 但是其它一些物質, 比如玉米糊或者一些天然花生醬 事實上會隨著力的變大 而變得更偏向固態性質。 其它還有一些會爬上旋轉的攪拌棒, 或者它們自己就能持續從燒杯中倒出, 一旦你開始這麼做。 儘管從物理學角度上來說, 番茄醬是一種更加複雜的混合物。 如果這還不夠,原料的平衡 比如還有天然增稠劑黃原膠的存在, 它也存在於其它水果飲料以及奶昔, 會意味著兩種不同的番茄醬 會表現出完全不同的行為。 但是絕大多數會有兩種性質: 當力量達到臨界值,醬會液化, 以及當你長時間施加一個很小的力 它也會有逐漸液化的傾向。 這意味著你可以 用兩種方法擠出番茄醬: 一種是持續地,緩慢地極小的晃動 並且保證你一直用力按壓, 或是你可以給瓶子施加 一個非常非常大的力。 真正專業的做法就是蓋上瓶蓋, 給瓶子一些短的,急速的晃動 來喚醒這樣的一些番茄微粒, 然後打開蓋子, 然後很好地控制倒在那些美味地薯條上。