How Does a Megaphone Work
If you want to make your voice sound louder to people far away，you can use a megaphone．Usually the sound waves of your voice travel outward in all directions．The megaphone makes the voice sound louder because it points the sound waves in only one direction and keeps them from spreading out．Thus，the sound is Intensified，or made stronger．
喊话筒是怎样起作用的
如果你想对远处的人们说话声音大一些，你可以使用喊话筒。通常你声音的声波向四面八方传去。喊话筒能使你的声音增大是因为它能使声波只朝一个方向传去，防止了声波扩散。这样声音就增大即声音变得更响亮。
Why Do Water Drops Form on a Cold Glass
The beads of water that form on a glass of lemonade or icecold water on a warm day have nothing to do with the water in the glass．They are beads of dew that have condensed from the air．They form when the warm air strikes the cold glass．The air becomes chilled，too．It gives up some of its moisture，which collects as dew drops on the glass．
为什么冷玻璃杯上会形成水滴
在热天里，柠檬水或冰水杯子上所形成的水珠，与杯子里的水没有什么关系。这些水珠是从空气中凝结起来的露水。当热空气碰到冷杯子时就形成这些水珠。这时空气也变冷了，这样就留下了一些水分，它们就像露水一样，聚集在杯子上。
How Does a Neon Light Work
The colourful neon signs on stores are made of long glass tubes filled with a special gas called neon．An electric transformer sends electricity through the colourless gas，making it glow brightly with an orangered light．Other gases make lights that are blue and green．
霓虹灯是怎样亮的
在商店上端，五颜六色的霓虹灯牌告示用长玻璃管做成的。玻璃管内充满一种叫做氖的特殊气体。当变压器将电流送入并通过这种无色气体时，就使它产生橘红色的亮光。其他气体可以产生蓝色和绿色的光。
When Was the Umbrella Invented
It seems natural to put up an umbrella to keep off the rain．But actually，the umbrella was not invented as protection against rain．The first umbrellas originated as sunshades which the slaves of ancient Egypt held over their masters．As the use of umbrellas spread to other countries，the people living in wetter countries discovered that umbrellas made good protection against the rain，too！
伞是什么时候发明的
打起伞来可以防雨淋，这似乎是很自然的。但实际上伞并不是作为防雨工具而发明的。第一批伞的诞生是作为遮荫用的。古埃及的奴隶就是撑开伞在他的主人头上挡太阳的。当伞的运用传到其他国家时，住在多雨国家的人们发现伞也是很好的防雨工具。
What Does SOS Stand For
SOS is the call for help from a ship at sea．Some people think that SOS means“Save Our Ship”．Actually，the code doesn’t stand for anything．It was chosen for a distress signal because it is an easy signal to send by wireless．It consists of three dots，three dashes，and three more dots．
SOS代表什么
SOS是船在海上航行时呼救的信号。有人认为SOS的意思就是救救我们的船。其实这个电码并不代表任何东西。SOS被选为遇难的呼救信号，因为它是一个易于无线电发报的信号。它由三点、三画又三点（…——…）所组成。
How Does a Drum Make Its Sound
Sounds are caused by vibrations．When you rap a drum sharply with a drumstick，the drumhead vibrates rapidly．As the drum vibrates，it disturbs the air around it in such a way that sound waves are produced．The sound is resonated，or increased，by the hollow drum shell．When the sound waves reach your ears，you hear the sound made by the drum．
鼓是怎样发出声音的
声音是由振动引起的。当你用鼓槌急剧地击鼓时，鼓面就迅速振动。当鼓振动时，激荡着周围的空气，这样就产生声波。空心的鼓体能使声音回响，即增大。当声波传到你耳朵时，你就听到了鼓所发出的声音。
Why Does the Whistle Sound LowerAfter the Train Passes
It is the train’s motion that changes the whistle’s pitch．When the train is moving toward you，the sound waves are crowded together．More waves strike your ears each second，and the whistle sounds high and shrill．As the train rushes by，the sound waves are stretched farther apart，and the pitch of the whistle seems lower．Because the engineer moves with．the train，he hears only one pitch．
为什么火车驶过以后汽笛声变得低下来
正是火车的运动改变着汽笛的音调。当火车正向着你开来时，声波是聚集在一起的。每秒钟有较多的声波涌进你的耳朵，从而汽笛声听起来又高又尖。当火车从旁边疾驶而过以后，声波也随着火车向前方扩展，从而汽笛声调好像变得低下来。火车司机是随着火车一起运动的，所以他听到的总是一种声调。
How Does a Florescent Lamp Work？
A florescent Lamp is a glass tube filled with a gas called mercury vapour．The inside of the tube is coated with a material called phosphorus．When the light is turned on，an electric current causes the gas to give off an invisible ultraviolet light．The ultraviolet light makes the phosphorus material inside the tube glow with a cool bright light．
荧光灯是怎样发亮的
荧光灯是一种充满气体，即水银气的玻璃管。在管子内部涂着一层物质，即磷。当灯电源接通时，电流就使气体发出一种看不见的紫外线，这种紫外线使管子里的磷发出明亮的白光。
How Does a Phonograph Record Work？
A phonograph record stores sound in the wavy groove on its surface．The groove represents the sound waves that were made by a musical instrument or a person’s voice．As the record spins，the groove makes the needle vibrate．The vibrations are turned into electrical signals and sent to the speaker．There，the signals are changed into sound waves like those made when the music was first recorded．
唱片是怎样发音的
唱片把声音贮藏在其表面的波纹里。这些波纹代表了乐器或人所发出的声波。当唱片旋转时，波纹使针头颤动。这种颤动变成电讯号并送到喇叭，在那里电讯号又变回声波，这种声波就是原先录下来的音乐声。
Why Does a Whip Crack
The cracking noise a whip makes when it is snapped is a small sonic boom．At the height of such a snap，the tip of the whip moves through the air so fast that it makes the surrounding air vibrate violently，producing a sharp sound wave．When the sound wave reaches our ears，we hear a loud cra-c-c-ck！
为什么鞭子会发出噼啪的响声
当把鞭子猛向空中一抽时所发出的噼啪声乃是一种小爆音。在这样猛一抽达到顶点时，鞭梢穿过空气迅速运动，致使周围的空气猛烈地颤动，从而发出一种尖锐的声波。当声波传到我们耳朵时，我们就听到响亮的噼啪声。
How Does a Magnifying Glass Work
A magnifying glass is a lens that is thicker in the middle than it is on the edges．When you hold a magnifying glass close to a page in a book，the light rays bounce off the page and pass up through the magnifying glass before they come to your eyes．The curved lens bends and spreads the light in such a way that the print looks much bigger than it really is．
放大镜是怎样放大物体的
放大镜是一种中间比旁边要厚的透镜。当你拿起放大镜靠近书页时，光线就从书页折回，通过放大镜，然后进入你的眼中。这种凸透镜使光线折射并扩大，从而使得印刷字迹看上去要比真正的大得多。
Why Does a Fire Smoke
When a long log in a fireplace burns，some of the burning wood is changed into invisible gases．The hot gases rise up the chimney and drift away with the air．Usually many tiny bits of ash and black specks of unburned carbon，called soot，are carried away in the rising cloud of gases．The soot and ash colour the gases gray and make them visible as smoke．
火为什么会冒烟
当一块木头在壁炉里燃烧时，一些燃烧的木柴变成了看不见的气体。这些热气沿着烟囱往上逸出，并和空气一起飘荡而去。常常有许多小粒灰烬和没有烧尽的黑色碳微粒，这些叫做烟灰，它们随着上升的气团一起飘走。这些烟灰使气体染成灰色，并使它们成为可以看得见的烟。
Why Is the Pipe Under a Sink Curved