首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
Narrator Listen to part of a discussion in a physics class. The professor is discussing Forces. Now get ready to answer
Narrator Listen to part of a discussion in a physics class. The professor is discussing Forces. Now get ready to answer
admin
2013-04-25
25
问题
Narrator
Listen to part of a discussion in a physics class. The professor is discussing Forces.
Now get ready to answer the questions. You may use your notes to help you answer.
What are two key factors of force description?
Professor Well, today we’d talk about Force and its representation.
Student A So what is force?
Professor Well, actually, a force is a push or pull upon an object resulting from the object’s interaction with another object. Whenever there is an interaction between two objects, there is a force upon each of the objects. When the interaction ceases, the two objects no longer experience the force. Forces only exist as a result of an interaction.
Student A interrupting
You mean if a force exists, there should be two objects. Am I right?
Professor That’s right. Er, ...For simplicity sake, all forces, interactions, between objects can be placed into two broad categories. One is contact force; the other is force resulting from action-at-a-distance.
Student B interrupting
Action-at-a-distance?
Professor Yeah, first let’s talk about contact force. Contact forces are types of forces in which the two interacting objects are physically in contact with each other. Examples of contact forces include frictional forces, tensional forces, normal forces, air resistance forces, and applied forces. These specific forces will be discussed in more detail later in Lesson 2, as well as in other lessons.
Student A Uh...so many forces fall into this category. Then, what is "force resulting from action-at-a-distance"?
Professor Er Action-at-a-distance forces are types of forces in which the two interacting objects are not in physical contact with each other, yet are able to exert a push or pull despite a physical separation. Examples of action-at-a-distance forces include gravitational forces, such as, the sun and planets exert a gravitational pull on each other despite their large spatial separation; even when your feet leave the earth and you are no longer in contact with the earth, there is a gravitational pull between you and the Earth. Next, electric forces, such as, the protons in the nucleus of an atom and the electrons outside the nucleus experience an electrical pull towards each other despite their small spatial separation; and magnetic forces, for example, two magnets can exert a magnetic pull on each other even when separated by a distance of a few centimeters. These specific forces will be discussed in more detail in other lessons.
Student B That’s magic! I am quite familiar with the phenomenon you mentioned just now, but before this class, I had no concept of these categories of forces.
Student A Er, I know very little about this, too.
Professor Actually, forces exist in our daily life. Force is a quantity which is measured using the standard metric unit known as the Newton. A Newton is abbreviated by an "N". To say "10.0 N" means 10.0 Newtons of force.
Student A interrupting
So Newton is the standard metric unit of force?
Professor That’s true. In fact, a force is a vector quantity. As we learned in an earlier unit, a vector quantity is a quantity which has both magnitude and direction. To fully describe the force acting upon an object, you must describe both the magnitude and the direction. Thus, "10 Newtons" is not a full description of the force acting upon an object. In contrast, "10 Newtons downwards" is a complete description of the force acting upon an object; both the magnitude, "10 Newtons", and the direction, "downwards", are given.
Student B Uh, that’s quite complex and easy to make a mistake.
Professor Yeah because a force is a vector which has a direction, it is common to represent forces using diagrams in which a force is represented by an arrow. Such vector diagrams were introduced in an earlier unit and will be used throughout your study of physics. The size of the arrow is reflective of the magnitude of the force and the direction of the arrow reveals the direction which the force is acting. Such diagrams are known as free-body diagrams. Furthermore, because forces are vectors, the influence of an individual force upon an object is often canceled by the influence of another force. For example, the influence of a "20 Newton upward" force acting upon a book is canceled by the influence of a "20 Newton downward" force acting upon the book. In such instances, it is said that the two individual forces "balance each other", meaning there would be no unbalanced force acting upon the book.
Student A That sounds interesting. Then, there should be other situations in which two of the individual vector forces cancel each other, the so-called balance, yet a third individual force exists that is not balanced by another force.
Professor That’s the point. Next time we will learn how to draw the free-body diagrams, which can help you to understand the situation more easily.
选项
A、Magnitude.
B、Weight.
C、Direction.
D、Power.
答案
AC
解析
本题为细节多选题,考查考生能否听懂和记住说话者提到的多个细节和事实。题目问:进行力的描述需要哪两大要素?从对话可知,描述一个力,要把握两个要素:力的大小和力的方向,所以选A和C。
转载请注明原文地址:https://jikaoti.com/ti/IFlYFFFM
0
托福(TOEFL)
相关试题推荐
CompletethefollowingnotesusingNOMORETHANTHREEWORDSforeachanswerIfrobbed,youshouldcontactyour【16】orDarling
TheproblemthatConstableGraydescribesis
ChooseyouranswersfromtheboxandwritethelettersA-Hnexttoquestions26-30.SharonandLesterhavedifferent(26)
A、funB、guessworkC、abilityA
CompletethenotesbelowbywritingNOMORETHANTHREEWORDSinthespacesprovided.TheGovernmentplanstogive【T14】$______to
STUDENTBANKINGNote:Maynotbeallowedallfacilitiesgiventoresidentstudents.FundingMustprovide【T14】______.Icans
STUDENTBANKINGNote:Maynotbeallowedallfacilitiesgiventoresidentstudents.FundingMustprovide【T14】______.Icans
STUDENTBANKINGNote:Maynotbeallowedallfacilitiesgiventoresidentstudents.FundingMustprovide【T14】______.Icans
CompletethediagrambywritingNOMORETHANTHREEWORDSinthebaresprovided.
Completethesentencesbelow.WriteNOMORETHANTHREEWORDSforeachanswer.TheBritishLibraryAllthelibraryroomstogethe
随机试题
A.尿少浮肿B.随气流窜C.积于管腔D.肢体困重痰的致病特点之一是
孕妇应尽量不用抗癫痫药的道理是
以下关于注意的说法中错误的是
临床医学研究中的知情同意原则,主要体现在
由药师或大专以上药学学历的技术人员担任并要保持相对稳定的是由药士或中专以上药学学历,其他人员应具有高中以上文化程度并经培训合格持证上岗的是
任何经济活动都可能有风险,面对风险人们的选择可能不同,针对可控性风险采取防止风险发生,减少风险损失,此风险对策属于______。
编制费用计划过程中最重要的方法是项目费用目标的分解,根据费用控制目标和要求的不同,可以分为()。
某科研单位由于体制转轨开始面向市场,单位原来实行的工资体系也因此受到冲击。科研人员对目前的收入极其不满,认为既不具有内部公平性,也不具备外部竞争性。鉴于以上情况,单位领导请来专家小组,对此进行诊断并提出相应对策。专家组采用因素比较法对单位内部工作岗位进行了
•Readtheinformationaboutcommercialbanks.•Choosethebestwordtofillineachgap,fromA,BorC.•Foreachquestion2
A、Hewantstoliveoffcampus.B、Thereareadvantagesanddisadvantagestolivingoffcampus.C、Livingspaceinthedormiscrow
最新回复
(
0
)