lesson 1 力学基本概念

mesh[

???

]

n.

网孔

,

网丝

,

网眼

,

圈套

,

陷阱

,

[

机

]

啮合

vt.

以网捕捉

,

啮合

,

编织

vi.

落网

,

相啮

合。

It is necessary to know the magnitudes of these forces for a variety of reasons. The distribution of the forces at the

boundaries

or

mating

surfaces

must

be

reasonable,

and

their

intensities

must

be

within

the

working

limits

of

the

materials composing the surfaces. For example

，

if the force operating on a sleeve bearing becomes too high, it will

squeeze out the oil film

薄膜

and cause metal

－

to

－

< br>metal contact, overheating

，

and rapid failure of the bearing

轴

承．

If the forces between gear teeth are too large, the oil film may be squeezed out from between them

．

This could

result in flaking

剥落

and spalling

碎裂

of the metal

，

noise

，

，

and eventual failure

．

In the study of

mechanics we are principally interested in determining the magnitude

，

direction

，

and location of the forces

．

由于很多原因

,

人们必须知道这些力的大小。这 些力在边界或在配合表面

(

啮合面

)< /p>

的分布必须合理，它们的

太小必须在构成配合表面

(

啮合面

)

的材料的工作极限 以内。例如，如果作用在一个套筒轴承上的力太大，它就

会将油膜挤出，造成金属与金属 的直接接触产生过热和使轴承快速失效。如果齿轮相啮合的齿之间的力过大，

就会将油膜 从齿间挤压出来。这会造成金属的剥落和碎裂，噪音增大，运动不精确，直至报废。在力学研究中，

我们主要关心力的大小、方向和作用点。

Some of the terms used in this phase

[feiz]

of our studies are defined below

．

我们将要用到的一些术语定义如下：

Force

Our earliest ideas concerning forces arose because of our desire to push

，

lift

，

or pull various objects

．

So

force

is

the

action

of

one

body

acting

on

another

．

Our

intuitive

concept

of

force

includes

such

ideas

as

place

of

applicat ion

，

direction

，

and magnitude

，

and these are called the characteristics of a force

．

力

关于力的最早概念是由于我们需要 推、举或拉各种物体而产生的。因此，力是物体之间的相互作用。

力的直观概念包括作用 点、方向和大小。这些称为力的要素。

Matter

Matter is any material or substance

；

if it is completely enclosed

，

it is called a body

．

物质

物质是任何材料或实体，如果它是全封闭的，则称为物体。

Mass

Newton

[‘nju:tn]

defined

mass

as

the

quantity

of

matter

of

a

body

as

measured

by

its

volume

and

density

．

This is not a very satisfactory definition because density is the mass of a unit volume

．

We can excuse Newton

by surmising that he perhaps did not mean it to be a definition

．

N evertheless

，

he recognized the fact that all bodies

possess some inherent property that is different from weight

．

Thus

，

a moon rock has a certain constant amount of

substance

，

even

though

its

moon

weight

is

different

from

its

earth

weight.

This

constant

amount

of

substance,

or

quantity of matter

，

is called the mass of the rock.

质量

牛顿 将质量定义为用物体的体积和密度来量度的、物体所含物质的量。因为密度是单位体积的质量，

< br>所以这不是一个很令人满意的定义。我们估计当时牛顿大概没有意识到他在下定义，因而我们可以原谅他。 不

过，他认识到这样一个事实，一切物体都具有某种与重量不同的内在性质。尽管一块月 球岩石在月亮上和地球

上的重量不同，但它的物质含量是不变的。这不变的物质含量就称 为岩石的质量。

Inertia

< br>[

????????

]

Inertial is the property of mass that causes it to resist any effort to change its motion

．

惯性

惯性是质量所具有的抵抗任何外力改变其本身运动状态的性质。

Weight

Weight is the force of gravity acting upon a mass. The following quotation is pertinent:

重量

< /p>

重量是作用在质量上的重力。下列引文确切地论述了质量和重量的关系：

< br>

The great advantage of

SI (International System of Units)

units is that there is one

，

and only one unit for each

physical quotation

—

the meter for length, the kilogram for mass

，

the Newton for force

，

the second for time

，

etc

．

To be

consistent with this unique feature

，

it follows that a given unit or word should not be used as an accepted technical

name

for

two

physical

quan tities

．

However,

for

generations

the

term

“

weight

”

has been

used

in both

technical

and

non-technical fields to mean either the force of gravity acting on a body or the mass of a body itself.

国际标准单位制的最大优越性是，对每一个物理量有一个， 而且只有一个单位——如长度单位为米，质量

单位为千克，力的单位为牛顿，时间单位为 秒等。为了与这种单一性相一致，一个给定的单位或词不能作为两

个物理量的技术名词。

但是许多年以来，

“重量”

这个词在技 术领域和非技术领域中都被用来既表示作用在一个

物体上的重力，又表示物体本身的质量 。

[

扩展

4]

：

CGPM

国际计量大会

(General

Conference

of

Weights

and

Measures),

法文简称

CGPM( Conference

Generale des Poids et Mesure s)

，在米制公约下，

CGPM

是最高 的权力机构，每四年召开一次大会，由各会员国