1 Scientists recently made public the tiniest electric motor ever1 built.You could stuff hundreds of them into the period at the end of this sentence.One day a similar engine might power a tiny mechanical doctor that would travel through your body to remove your disease.
    2 The motor works by shuffling atoms between two molten metal droplets in a carbon nanotube.One droplet is even smaller than the other.When a small electric current is applied to the droplets,atoms slowly get out of the larger droplet and join the smaller one.The small droplet grows — but never gets as big as the other droplet and eventually bumps into the large droplet.As they touch,the large droplet rapidly sops up the atoms it had previously lost.This quick shift in energy produces a power stroke.2
    3 The technique exploits the fact that surface tension — the tendency of atoms or molecules to resist separating — becomes more important at small scales3.Surface tension is the same thing that allows some insects to walk on water.
    4 Although the amount of energy produced is small — 20 microwatts — it is quite impressive in relation to the tiny scale of the motor4.The whole setup5 is less than 200 nanometers on a side,or hundreds of times smaller than the width of a human hair.If it could be scaled up to the size of an automobile engine6,it would be 100 million times more powerful than a Toyota Camry's 225 horsepower V6 engine.
    5 In 1988,Professor Richard Muller and colleagues made the first operating micromotor,which was 100 microns across7,or about the thickness of a human hair.In 2003,Zettl's group created the first nanoscale motor.In 2006,they built a nanoconveyor,which moves tiny particles along like cars in a factory.
    6 Nanotechnology engineers try to mimic nature,building things atom-by-atom.Among other things,nanomotors could be used in optical circuits to redirect light,a process called optical switching.Futurists envision a day when nanomachines,powered by nanomotors,travel inside your body to find disease and repair damaged cells.
    練習(xí)：
    1.Paragraph 2 _____
    2.Paragraph 4 _____
    3.Paragraph 5 _____
    4.Paragraph 6 _____
    A An Introduction of a Toyota's 225 Horsepower V6 Engine
    B A Description of the Nanomotor in Terms of Power and Size
    C Surface Tension
    D Previous Inventions of Nanoscale Products
    E The Working Principle of the Nanomotor
    F Possible Fields of Application in the Future
    5.Doctors envision that the nanomotor would travel through human bodies to _____.
    6.Surface tension means the tendency of atoms or molecules to _____.
    7.Nanoconveyors could be used to _____.
    8.Applying a small electric current causes atoms to _____.
    A remove disease
    B resist separating
    C shuffle between two molten metal droplets
    D power nanomachines
    E sop up molecules from the large droplet
    F transport nanoscale objects
    答案與題解：
    1.E 第二段介紹了納米發(fā)動機(jī)的工作原理。兩小滴金屬熔液通上微弱電流，大的小滴的原子就會緩慢逸出，加入小的小滴，后者體積不斷增大，到一定階段，就會與前者碰撞，這時，大的小滴便奪回它失去的原子，這就是一次power stroke（動力行程，動力沖程），此時就會產(chǎn)生發(fā)動機(jī)的動力。原子如此來來去去運動，就像發(fā)動機(jī)活塞一樣。這就是納米發(fā)動機(jī)的工作原理。所以，E是答案。
    2.B 第四段描述了納米發(fā)動機(jī)的功率（20微瓦）和體積（200納米）。選項B用“A description of the nanomotor in terms of power and size”概括本段大意，很準(zhǔn)確，所以B是答案。
    3.D 第五段介紹了發(fā)明納米發(fā)動機(jī)之前的一些納米等級的機(jī)械產(chǎn)品，如體積大一些的納米發(fā)動機(jī)，微型發(fā)動機(jī)，納米傳送帶，納米機(jī)器等。選項D概括了本段的大意，所以是答案。
    4.F 第六段預(yù)想了納米發(fā)動機(jī)的用途，如用于光電路以改變光的方向（redirect light）和驅(qū)動納米機(jī)器進(jìn)入人體，消滅病灶。選項F是答案，因為“Possible fields of application in the future”概括了本段的大意。
    5.A 答案是A.題干出現(xiàn)doctors envision，選項的內(nèi)容應(yīng)與醫(yī)學(xué)有關(guān)，選項A是remove disease，正好與題干的內(nèi)容相配，是答案。短文第一段和最后一段也提到納米發(fā)動機(jī)進(jìn)入人體消滅病灶的可能性，證明選A是正確的。
    6.B 選B的依據(jù)是第三段第一句“surface tension—the tendency of atoms or molecules to resist separating—becomes more important at small scales”。
    7.F 題干的nanoconveyor提示我們，納米傳送帶的功能自然是傳送納米等級的物體，所以F是答案。
    8.C 題干的Applying a small electric current ……在第二段能找到，該段講的是納米發(fā)動機(jī)的工作原理。如果了解原子在兩小滴金屬熔液中來回運動，產(chǎn)生動力，就會知道C是答案。