Lecture 5 物理测量
Word Tips
bracket n.括号 power n.[数]乘方；幂
density n.密度 square v.平方
aluminum n.铝 plausible adj.有道理的；可信的
calibration n.标定；校准；（温度计或其他仪表上的）刻度
mass n.质量
Listen to the following recording and answer questions 1-3.
1）A.length，time and mass
B.speed，volume and density
C.time，matter and energy
D.light，heat and electricity
2）A.the uncertainty in measurement
B.the importance of measurement
C.the correct way of measurement
D.the fundamental quantities
3）A.Someone who is lying in bed is longer than someone who stands up.
B.Someone who is lying in bed is shorter than someone who stands up.
C.Someone who is lying in bed is the same length as someone who stands up.
D.All other quantities can be derived from the three fundamental quantities.
4）A.his grandmother
B.his bed
C.an aluminum bar
D.all the students
听力原文
I already introduced，as you see there，length，time and mass and we call these the three fundamental quantities in physics.I will give this the symbol capital L for length capital T for time，and capital M for mass.All other quantities in physics can be derived from these fundamental quantities.I’ll give you an example.I put a bracket around here.I say [speed]and that means the dimensions of speed.The dimensions of speed is the dimension of length divided by the dimension of time.So I can write for that：[L]divided by [T].Whether it’s meters per second or inches per year that’s not what matters.It has the dimension length per time.Volume would have the dimension of length to the power three.Density would have the dimension of mass per unit volume so that means length to the power three.All-important in our course is acceleration.We will deal a lot with acceleration.Acceleration，as you will see，is length per time squared.The unit is meters per second squared.So you get length divided by time squared.So all other quantities can be derived from these three fundamental.So now that we have agreed on the units.We have the meter，the second and the kilogram.We can start making measurements.
Now，all-important in making measurements which is always ignored in every college book is the uncertainty in your measurement.Any measurement that you make without any knowledge of the uncertainty is meaningless.I will repeat this.I want you to hear it tonight at 3:00 when you wake up.Any measurement that you make without the knowledge of its uncertainty is completely meaningless.
My grandmother used to tell me that…at least she believed it…that someone who is lying in bed is longer than someone who stands up.And in honor of my grandmother I’m going to bring this today to a test.I have here a setup where I can measure a person standing up and a person lying down.It’s not the greatest bed，but lying down.I have to convince you about the uncertainty in my measurement because a measurement without knowledge of the uncertainty is meaningless.And therefore，what I will do is the following.I have here an aluminum bar and I make the reasonable，plausible assumption that when this aluminum bar is sleeping，when it is horizontal，that it is not longer than when it is standing up.If you accept that，we can compare the length of this aluminum bar with this setup and with this setup.At least we have some kind of calibration to start with.I will measure it.You have to trust me.During the three months，we have to trust each other.
Questions：
1.According to the professor，what are the three fundamental quantities in physics？
2.What is always ignored in every college book？
3.What does the professor’s grandmother believe？
4.What is the professor going to measure？
参考译文
我们已经讲过长度、时间、质量，他们被称为三个基本物理量。大写的L表示长度，大写T表示时间，M表示质量。从这三个基本物理量，可以导出其他所有的物理量。给你们举个例子，在这儿加上括号。我说[S]，这表示速度的大小。长度除以时间，即为速度。速度为长度除以时间。可以记作[L]/[T]，无论是米/秒，或者英寸/年，都可以。只要是单位时间的长度大小就可以。体积就是将长度三次方即可得出；密度则是单位体积的质量，即质量除以长度的三次方。加速度是本课程的重点，我们会经常提及加速度，加速度是长度除以时间的平方。单位是m/s。所以求他的公式是长度除以时间的平方。你也能通过这三个基本量导出其他的物理量。现在我们已经把单位确定了，有了米、秒、千克。我们可以开始测量了。
物理的测量中有一个内容十分重要，很多高校教材没有提到。那就是测量的不确定性。如果不考虑不确定性，那么任何测量都是没有意义的。我会反复地讲这一点，让你们在凌晨三点醒来时，想起的第一件事情仍是这句话。如果不考虑不确定性，那么任何测量都是没有意义的。
我的祖母确信，她也曾经告诉我，一个站着的人没有躺着的人高。今天我要做一个实验来纪念我的祖母。这里有两个装置，一个用来测量平躺的人，一个用来测量站立的人。这床虽然寒酸了点，但躺一个人还是没有问题的。测量存在不确定性，我将向各位证实这点。不考虑不确定性的测量是没有意义的。下面我们开始实验，我这儿有一根铝条。我们可以合理地假设不管铝条水平放置还是竖直放置，其长度是一样的。而我们通过实验可以比较，铝条这样测量和那样测量的长度是一样的。首先我们从校准开始，现在我们开始测量，大家必须信任我。在接下来的三个月里，我们要相互信任。
参考答案
1.A 2.A 3.A 4.C