问题 选择题

下列实例中,有利于增大压强的是(  )

A.书包带做得扁而宽

B.骆驼脚掌长得很大

C.啄木鸟有尖硬的喙

D.泥鳅体表有层黏液

答案

A、在压力不变时,扁而宽的带子增大了受力面积使压强减小了,不合题意;

B、在压力不变时,宽在的脚掌增大了受力面积,使压强减小了,不合题意;

C、在压力不变时,尖硬的喙减小了受力面积,压强增大了,符合题意;

D、泥鳅体表的黏液使其变得光滑,减小了摩擦力,与压强无关,不合题意.

故选C.

阅读理解

阅读理解。

     New technology that can " see" through clothing and detect what 's underneath can now be used to scan

crowds, making it a potentially effective tool to prevent terrorist attacks in public places.

     The Thru Vision T5000 camera picks up Terahertz rays,or T-rays, which are naturally sent out by all

objects and can pass through clothes or even walls. The camera can then detect metallic and nonmetallic

objects hidden under clothing on still or moving subjects without showing any body detail.

     While similar technology is seen at airports around the world, the T5000 is designed to be used in large,

open areas. With a range of 25 meters, the T5000 can screen people in public places, thus avoiding

bottle-necks at border crossing or security checkpoints. It also means people can be screened without

knowing it.

     The technology develops from British astronomers ' work in studying dying stars. Astronomers use T-ray

cameras to see through dust and clouds in space. The company sees uses for its camera at other sites where

political or business activities take place.

     For privacy concerns,Thru Vision Chief Executive Clive Beattie said the image produced by the camera

did not show detailed parts of the body." It's almost a shining light bulb (灯泡)." Beattie said. "You don' t see

the detail that people might be concerned about." In London' s busy Piccadilly Circus-which is already filled

with closed-circuit surveillance (监视) cameras- reaction to the new technology was mixed. Some said the

camera was going too far and violating privacy,but others said they are willing to put safety before privacy

concerns." There ' s surveillance everywhere anyway," said one commuter. "I don' t think it' s much of a

difference. I don' t care that they can see through me because they can see me anyway."

     Some experts said the privacy violation of the camera was not worth the benefit. " What we should

consider is how much we want to lose our privacy in order to obtain a sort of national security," said David

Murakami Wood, director of the Surveillance Studies network,which deals with surveillance and privacy

problems." In most cases this isn' t real security-it 's a sense of safety that has very little real effect."

1. What can we learn about T5000?

A. It can detect metallic and nonmetallic objects underneath.

B. It can see through clothing or walls by sending out T-rays.

C. It was first used to observe stars by astronomers.

D. It is widely used at airports around the world.

2. What is the most probable purpose of the new invention?

A. To improve people ' s life standard.

B. For scientific research.

C. For commercial benefits.

D. For safety reasons.

3. Which is most probably the opinion of people on using the new camera?

A. Some agree to its use as it is new technology to protect privacy.

B. Some agree to its use because safety is the most important.

C. Some don' t agree to its use because it makes no difference.

D.Some people don' t care because they know little about it.

4. What' s the main idea of the last paragraph?

A. Safety is more important than privacy.

B. T5000 is more beneficial than harmful.

C. T5000 does not really provide security.

D. It's not worth giving up privacy for safety.

多项选择题