问题 选择题

一般情况下,近地面的风受到几个力的作用形成(  )

A.1

B.2

C.3

D.4

答案

答案:C

题目分析:近地面的风受水平气压梯度力、摩擦力、地转偏向力的影响。所以风向由高压指向低压并与等压线斜交。故选C。

点评:本题组难度较低,对于此类试题,解答本题组的关键是学生要掌握力与风向的关系知识。

【方法指导】

三种力与两种风向的规律:

三种力即水平气压梯度力、地转偏向力、摩擦力 ①水平气压梯度力:地表受热不均,使同一水平面上产生了气压差异。单位距离间的气压差叫做气压梯度。只要水平面上存在着气压梯度,就产生了促使大气由高气压区流向低气压区的力,这个力称为水平气压梯度力。在这个力的作用下,大气由高气压区向低气压区作水平运动,这就形成了风。因此,水平气压梯度力是形成风的直接原因。其方向垂直于等压线,从高压指向低压。②. 地转偏向力:由于地球自转,地球表面的物体在沿水平方向运动时,其运动方向发生一定的偏转,我们把促使物体水平运动方向产生偏转的力,称为地转偏向力。其方向为:在北半球向右偏转,在南半球向左偏转。地转偏向力的方向总是与风向垂直,其只改变风向,不能改变风速。③. 摩擦力:是指地面与空气之间以及运动状况不同的空气层之间互相作用而产生的阻力。其方向总是与风向相反。因而摩擦力不仅能改变风向,而且可减小风速。

两类风即高空风和近地风 ①. 高空风:高空大气中的风向,是水平气压梯度力和地转偏向力二力共同作用的结果。风向与等压线平行。如图。

②. 近地风:近地面大气中的风向,是水平气压梯度力、地转偏向力和摩擦力三力共同作用的结果。风向与等压线之间成一夹角。如右图。

注意:在判断风向时,一定要审清题意,看是高空风还是近地风。

完形填空
A rich man was camping alone on a hill. One day it began to rain and the rain made the tent wet.
At last he 1 make his way home. As he passed a beautiful house he 2 to look for rest. A lady in 3 
walked past him with her 4 holding up high. Following her were her two pretty daughters. They
stopped and stared at him  5  .
“Who are you? We don’t like tramps(流浪汉)going around 6 our home .”one of them shouted.
“Go away at once. ”cried the other.
“But I’m not a  7 . ”said the man, “All I want is food and stay for the night.”
“How 8 you come here? Go away at once!” they 9 “We don’t like your feet around our house.
Go, go!”
The man moved on and reached a  10 house. On entering it he saw a 11   preparing their
supper. Though the light was 12 and the furniture was poor, it made him feel 13  and comfortable.
“Can I have some 14   and rest for the night?” he asked. “Of course, friend,” said the woman,
bringing forward a little chair for him. “We are going to15 our supper. Come and 16 us.”
The food was not  17 but they shared it with the stranger. That night they let him sleep on their
bed  18  they themselves used the stable(厩). Early the next morning, the man said good-bye to them. Their   19  left him a memory full of thanks.
When he reached home he   20  ordered a lovely house to be built for the couple in the woods.
小题1:
A.had to B.must C.shouldD.would
小题2:
A.triedB.managedC.askedD.stopped
小题3:
A.sightB.clothC.silkD.trouble
小题4:
A.noseB.headC.eyesD.hands
小题5:
A.curiously B.suddenlyC.surprisinglyD.angrily
小题6:
A.aroundB.overC.toD.at
小题7:
A.madamB.trampC.thiefD.stranger
小题8:
A.doB.canC.willD.dare
小题9:
A.explainedB.continuedC.repeatedD.announced
小题10:
A.bigB.smallC.lovelyD.dirty
小题11:
A.womanB.manC.personD.couple
小题12:
A.weakB.brightC.darkD.strong
小题13:
A.sadB.coldC.warmD.clean
小题14:
A.clothB.foodC.lightD.chair
小题15:
A.prepareB.cookC.buyD.have
小题16:
A.joinB.helpC.attendD.enjoy
小题17:
A.enoughB.scaryC.shortD.lot
小题18:
A.andB.whileC.thenD.when
小题19:
A.coldnessB.sicknessC.kindnessD.thank
小题20:
A.quicklyB.finallyC.happilyD.quietly
单项选择题