Simple Science Experiments

Science doesn't only happen in laboratories full of expensive equipment and people in white coats. Many basic ideas in physics, chemistry and biology can be shown on a kitchen table with things you already have at home: vinegar, salt, milk, a glass bottle or a sewing needle.

科学并不只发生在摆满昂贵仪器、人人身穿白大褂的实验室里。物理、化学和生物学中的许多基本原理，用家里现成的东西就能在厨房餐桌上演示出来，比如醋、盐、牛奶、玻璃瓶或缝衣针。

Experiments like these are fun, but they also teach something useful: the world follows rules that we can discover and understand. When a child watches baking soda fizz in vinegar and asks why, they are doing what scientists do: watching carefully and looking for an explanation. Here are some of the best experiments to try at home, with a short explanation of what is really going on in each one.

这样的实验很有趣，也能让人学到有用的东西：世界遵循着我们能够发现和理解的规律。当孩子看到小苏打在醋里冒泡并问“为什么”时，他做的正是科学家所做的事：仔细观察，寻找解释。下面介绍几个最值得在家做的实验，并简要说明每个实验背后真正发生了什么。

Baking soda and vinegar is the classic piece of kitchen chemistry. Baking soda is sodium bicarbonate, a base, and vinegar contains acetic acid. When the two meet, they react and produce carbon dioxide gas, water and a salt called sodium acetate. The carbon dioxide is what makes the mixture fizz and bubble.

小苏打加醋是厨房化学的经典实验。小苏打就是碳酸氢钠，属于碱，而醋中含有醋酸。两者相遇就会发生反应，生成二氧化碳气体、水和一种叫醋酸钠的盐。让混合物嘶嘶作响、不断冒泡的，正是二氧化碳。

For a better show, put a pile of baking soda in a small cup or bottle, then add a few drops of food coloring and a squirt of dish soap to the vinegar before you pour it in. The soap traps the gas in bubbles, so you get a thick, colorful foam that pours over the sides like lava. The idea behind it, that acids and bases react with each other, is one of the basics of chemistry. Acids and bases are all around us: in lemon juice and soap, in cleaning products and in our own stomachs, where hydrochloric acid helps break down food.

想让效果更好看，可以在小杯子或瓶子里堆上一些小苏打，然后在倒入醋之前，先往醋里加几滴食用色素和少许洗洁精。洗洁精会把气体包在泡泡里，于是形成一团浓密的彩色泡沫，像熔岩一样从边缘溢出来。这个实验背后的道理，即酸和碱会相互反应，是化学的基础知识之一。酸和碱在我们身边随处可见：柠檬汁和肥皂里有，清洁用品里有，我们自己的胃里也有，胃里的盐酸帮助分解食物。

Drop a few raisins into a glass of sparkling water or clear soda. At first they sink to the bottom. Then, one by one, they slowly rise to the top, sink again and keep going up and down for a long time. The raisins are showing you how density and buoyancy work.

往一杯气泡水或透明汽水里丢几颗葡萄干。一开始它们会沉到杯底。接着，它们一颗接一颗地慢慢浮上水面，又沉下去，就这样上上下下持续很久。葡萄干向你展示了密度和浮力是怎样起作用的。

A raisin sinks because it is denser than the liquid. On the bottom, though, bubbles of carbon dioxide stick to its wrinkled skin. Each bubble works like a tiny life jacket: the raisin and its bubbles take up more space without getting much heavier, so together they become less dense than the water and float up. At the surface many of the bubbles burst, the raisin is denser than the water again, and down it goes. This goes on until the drink goes flat. Many fish use a similar trick: they control their depth by adding gas to an organ called the swim bladder or letting gas out of it.

葡萄干会下沉，是因为它的密度比液体大。不过沉在杯底时，二氧化碳气泡会附着在它皱巴巴的表皮上。每个气泡都像一件小小的救生衣：葡萄干和它身上的气泡占据了更大的空间，重量却几乎没有增加，于是两者加起来的密度比水小，便浮了上去。到了水面，许多气泡破裂，葡萄干的密度又比水大了，于是再次下沉。这个过程会一直持续到汽水跑完气为止。许多鱼也用类似的办法：它们通过向一个叫鳔的器官充气或放气来控制自己所处的深度。

Growing crystals is one of the most rewarding experiments you can do at home, and all you need is salt or sugar, hot water and patience. The process is called crystallization, and it shows how neatly matter is organized at the smallest scale.

培养晶体是在家里做起来最有成就感的实验之一，只需要盐或糖、热水和耐心。这个过程叫作结晶，它展示了物质在最微小的尺度上排列得多么整齐。

Stir salt into hot water until no more will dissolve. This is called a saturated solution. Pour it into a glass and hang a rough piece of string into it from a pencil laid across the top. Over the next few days the water slowly evaporates, and the liquid that is left can't hold all the salt. The extra salt comes out of the solution and settles on the string. Little by little, small crystals with flat faces and straight edges appear. Salt crystals are often shaped like tiny cubes, because inside them sodium and chloride ions are arranged in a cubic pattern that repeats millions of times. Nobody designs this shape; it comes from the chemistry itself.

把盐加进热水里搅拌，直到再也溶解不了为止。这样得到的叫饱和溶液。把它倒进玻璃杯，在杯口横放一支铅笔，在铅笔上系一段粗糙的细绳，让绳子垂进溶液里。接下来几天，水慢慢蒸发，剩下的液体容纳不了全部的盐，多余的盐便从溶液中析出，附着在绳子上。渐渐地，会出现一些面平、棱直的小晶体。盐的晶体常常呈小立方体的形状，因为在晶体内部，钠离子和氯离子按立方体的图案排列，这种图案重复了千百万次。这种形状不是谁设计出来的，而是由化学本身决定的。

This classic experiment shows the force of the air around us. You need a glass bottle whose neck is a little narrower than a peeled hard-boiled egg, and a few thin strips of paper. With an adult's help, light the paper, drop it into the bottle and quickly set the egg on the opening. Soon after the flame goes out, the egg is squeezed through the neck and drops into the bottle, sometimes with a loud pop.

这个经典实验展示了我们周围空气的力量。你需要一个瓶口比剥了壳的熟鸡蛋稍窄的玻璃瓶，以及几条细纸条。在大人的帮助下点燃纸条，丢进瓶子里，然后迅速把鸡蛋放在瓶口上。火焰熄灭后不久，鸡蛋就会被挤过瓶颈，掉进瓶子里，有时还会发出响亮的“噗”的一声。

Here is what happens. The fire heats the air in the bottle, the air expands, and some of it escapes past the egg. When the flame goes out, the air that is left cools and its pressure drops. Now the air outside pushes harder than the air inside, and it forces the egg into the bottle. People often say that the fire uses up the oxygen, but that has only a small effect; the cooling of the air does most of the work. The same difference in pressure makes suction cups stick to tiles and lets you drink through a straw. We rarely notice air pressure, but at sea level it presses on every square centimeter of your body with the weight of about one kilogram.

原理是这样的。火加热了瓶内的空气，空气膨胀，一部分从鸡蛋旁边逸出。火焰熄灭后，剩下的空气冷却下来，压强随之降低。这时瓶外空气的压力比瓶内大，就把鸡蛋推进了瓶子。人们常说是火把氧气烧光了，但这一点影响很小，起主要作用的是空气冷却。同样的压强差让吸盘能吸在瓷砖上，也让我们能用吸管喝东西。我们很少察觉到大气压的存在，但在海平面上，它压在我们身体每一平方厘米上的力，大约相当于一千克物体的重量。

You can make a working compass with a steel sewing needle, a small magnet, a bowl of water and a leaf or a thin slice of cork. Stroke the needle with one end of the magnet about 30 times, always in the same direction. This lines up tiny magnetic regions inside the steel and turns the needle into a weak magnet for a while. Lay the needle on the leaf and float it on still water. It will slowly turn until it points north and south, in line with Earth's magnetic field.

用一根钢制缝衣针、一块小磁铁、一碗水，再加一片树叶或一薄片软木，就能做出一个能用的指南针。用磁铁的一端沿同一个方向摩擦缝衣针大约30次。这样钢里面微小的磁性区域就会朝同一方向排列，缝衣针在一段时间内会变成一块弱磁铁。把针放在树叶上，让树叶浮在平静的水面上。针会慢慢转动，直到指向南北方向，与地球磁场保持一致。

The compass is one of the great inventions in the history of navigation. In 1088 the Chinese scholar Shen Kuo described a magnetized needle that pointed north and south, and a few decades later Chinese sailors were using compasses at sea. By the end of the 12th century they had reached Europe too. For centuries nobody knew why they worked. Only in 1600 did the English scientist William Gilbert suggest that Earth itself behaves like a giant magnet. Earth's magnetic field does more than guide compass needles: it also turns aside most of the solar wind, a stream of charged particles from the Sun, and so helps protect our atmosphere.

指南针是航海史上的伟大发明之一。1088年，中国学者沈括记载了一种能指向南北的磁化针。几十年后，中国水手已经在海上使用指南针了。到12世纪末，指南针也传到了欧洲。几百年来，没有人知道它为什么能指向南北。直到1600年，英国科学家威廉·吉尔伯特才提出，地球本身就像一块巨大的磁铁。地球磁场的作用不只是给指南针指方向，它还能使大部分太阳风偏转。太阳风是来自太阳的带电粒子流，地球磁场因此有助于保护我们的大气层。

Pour some whole milk into a shallow plate and add drops of different food coloring near the middle. Now dip a cotton swab in dish soap and touch it to the center of the milk. The colors suddenly rush outward and swirl around the plate in bright, changing patterns. Few experiments you can do at home look this impressive.

在一个浅盘里倒些全脂牛奶，在靠近中间的地方滴几滴不同颜色的食用色素。然后用棉签蘸一点洗洁精，碰一下牛奶的中心。颜色会突然向四周散开，在盘子里旋转，形成鲜艳而不断变化的图案。在家能做的实验中，很少有这样好看的。

The explanation has to do with surface tension and fat. Water molecules at the surface of the milk pull on each other, so the surface acts a bit like a thin, stretched skin. Soap weakens this pull where it touches the milk. The rest of the surface, which still pulls strongly, drags the liquid away toward the edges and carries the colors with it. At the same time, soap molecules attach to tiny drops of fat and protein in the milk and keep the liquid moving for a while. The food coloring simply makes this movement visible. Soap cleans greasy plates in a similar way: one end of a soap molecule is attracted to water and the other end to fat, so soap surrounds bits of grease and lets the water wash them away.

这与表面张力和脂肪有关。牛奶表面的水分子彼此吸引，所以表面就像一层薄薄的、绷紧的膜。洗洁精碰到牛奶的地方，这种吸引力就会变弱。其余部分的表面仍在用力拉扯，于是把液体拉向边缘，颜色也随之被带走。与此同时，洗洁精分子会附着在牛奶中细小的脂肪和蛋白质颗粒上，让液体继续流动一段时间。食用色素只是让这种运动变得看得见。洗洁精清洗油腻盘子的道理也差不多：洗洁精分子一端亲水，另一端亲油，于是能把油污包裹起来，让水把它们冲走。

Invisible ink isn't only a children's game. Spies used it for centuries, including during the American Revolution and both World Wars. The simplest version uses lemon juice. Dip a cotton swab in lemon juice and write a message on white paper. Let it dry completely, and the writing disappears. To read it, ask an adult to run a hot iron over the paper, and the letters slowly appear in brown.

隐形墨水不只是孩子们的游戏。几百年来，间谍们一直在使用它，美国独立战争和两次世界大战期间都有人用过。最简单的隐形墨水是柠檬汁。用棉签蘸上柠檬汁，在白纸上写一段话。等它完全干透，字迹就消失了。要读出来，可以请大人用热熨斗在纸上熨一熨，字迹就会慢慢显现出棕色。

The chemistry is simple. Lemon juice contains sugars, citric acid and other substances. When they are heated, they break down and start to burn at a lower temperature than paper does, so the writing turns brown while the paper around it stays white. Part of this change is oxidation, a reaction with the oxygen in the air. Oxidation is one of the most common chemical reactions around us: it helps turn a cut apple brown and old paper yellow, and it is also what makes iron rust.

其中的化学原理很简单。柠檬汁里含有糖、柠檬酸和其他物质。这些物质受热后会分解，而且开始焦化的温度比纸低，所以字迹变成棕色时，周围的纸仍然是白的。这种变化有一部分是氧化，也就是与空气中的氧气发生反应。氧化是我们身边最常见的化学反应之一：切开的苹果变褐、旧纸发黄都与它有关，铁会生锈也是因为氧化。

Many famous scientists started out with very simple equipment. Michael Faraday grew up poor in London and had little schooling. At 14 he became an apprentice to a bookbinder, read the science books that passed through the shop and tried out their experiments with homemade equipment. Later, working at the Royal Institution, he discovered electromagnetic induction in 1831. This is the principle behind the generators that produce most of our electricity today.

许多著名科学家都是从非常简陋的器材起步的。迈克尔·法拉第在伦敦的一个贫苦家庭长大，几乎没受过什么学校教育。14岁时，他到一位装订商那里当学徒，读了经手的科学书籍，还用自制的器材做书里的实验。后来他在英国皇家研究院工作，于1831年发现了电磁感应。如今为我们提供大部分电力的发电机，就是基于这一原理。

Doing science is less about equipment than about a way of thinking: asking questions, planning tests, predicting what will happen and changing your ideas when the evidence says so. These skills can be learned at any age and on any budget. An experiment that doesn't go as expected isn't a failure if it leads to a new question. Some important discoveries began as surprises: Alexander Fleming found penicillin in 1928 when mold grew on one of his dishes of bacteria, Wilhelm Röntgen discovered X-rays in 1895, and Percy Spencer came up with the microwave oven after a chocolate bar melted in his pocket while he stood next to radar equipment.

做科学与其说靠器材，不如说靠一种思维方式：提出问题，设计检验，预测结果，并在证据面前修正自己的想法。这些能力在任何年龄、用任何预算都可以培养。一个实验没有按预期进行，只要它引出了新的问题，就不算失败。一些重要的发现就始于意外：1928年，亚历山大·弗莱明在一个细菌培养皿中发现长了霉菌，由此发现了青霉素；1895年，威廉·伦琴发现了X射线；珀西·斯宾塞站在雷达设备旁时，口袋里的巧克力棒融化了，他由此想到了微波炉。

Science is everywhere at home: in the bubbles in a glass of soda, the frost on a winter window, the colors of a sunset and the way soap removes grease. All of these everyday things can be explained, and many of them can be tested with simple experiments. In some ways a home is a good laboratory, because the questions come from real life.

家里处处都有科学：一杯汽水里的气泡，冬天窗户上的霜花，日落时的色彩，还有肥皂去除油污的方式。这些日常现象都能得到解释，其中很多还能用简单的实验来验证。从某种意义上说，家是一个不错的实验室，因为问题都来自真实的生活。

So when something in the kitchen, garden or bathroom surprises you, don't simply move on. Stop, look closely and try to work out what is behind it: a force, a chemical reaction or something alive. Noticing something odd and asking why is exactly how scientists begin.

所以，当厨房、花园或浴室里有什么事情让你感到意外时，不要就这样走开。停下来，仔细看，试着弄清楚背后是什么：一种力、一个化学反应，还是某种生命活动。注意到奇怪的现象并问一句“为什么”，科学家正是这样开始的。