Ⅰ 杠杆原理的文章(短的)
阿基米德在《论平面图形的平衡》一书中最早提出了杠杆原理。他首先把杠杆实际应用中的一些经验知识当作"不证自明的公理",然后从这些公理出发,运用几何学通过严密的逻辑论证,得出了杠杆原理。这些公理是:(1)在无重量的杆的两端离支点相等的距离处挂上相等的重量,它们将平衡;(2)在无重量的杆的两端离支点相等的距离处挂上不相等的重量,重的一端将下倾;(3)在无重量的杆的两端离支点不相等距离处挂上相等重量,距离远的一端将下倾;(4)一个重物的作用可以用几个均匀分布的重物的作用来代替,只要重心的位置保持不变。相反,几个均匀分布的重物可以用一个悬挂在它们的重心处的重物来代替;似图形的重心以相似的方式分布……正是从这些公理出发,在"重心"理论的基础上,阿基米德又发现了杠杆原理,即"二重物平衡时,它们离支点的距离与重量成反比。"
阿基米德对杠杆的研究不仅仅停留在理论方面,而且据此原理还进了一系列的发明创造。据说,他曾经借助杠杆和滑轮组,使停放在沙滩上的桅船顺利下水。在保卫叙拉古免受罗马海军袭击的战斗中,阿基米德利用杠杆原理制造了远、近距离的投石器,利用它射出各种飞弹和巨石攻击敌人,曾把罗马人阻于叙拉古城外达3年之久。
这里还要顺便提及的是,在我国历史上也早有关于杠杆的记载。战国时代的墨家曾经总结过这方面的规律,在《墨经》中就有两条专门记载杠杆原理的。这两条对杠杆的平衡说得很全面。里面有等臂的,有不等臂的;有改变两端重量使它偏动的,也有改变两臂长度使它偏动的。这样的记载,在世界物理学史上也是非常有价值的,而且墨子的发现比阿基米德早了约二百年。
Ⅱ 英语作文can you play the guitar
1.科技小制作的特点 科技小制作的特点就在于一个“小”字。“小”在哪里呢?(1)结构简单。一般只要制做几个零件,再组装起来就做好了。(2)材料好找。很多材料在家里就可以找到,如空纸盒、牙膏皮、泡沫塑料、罐头筒、废圆珠笔芯、坏了的玩具、铁丝、铁片等。(3)加工容易。多数项目工艺技术要求低,小学生可以掌握。(4)花钱少。有些项目甚至可以不花钱,不会增加家庭负担。(5)见成果快。不少项目只要一天、半天就可以做成,这符合少年儿童心理,容易推广普及。2.活动形式(1)开设科技课,使学生普遍受到科学教育,并辅导学生制作。(2)建立兴趣小组,辅导学生制作。(3)鼓励学生自己选题,独立完成小制作,必要时给予适当的辅导。3.活动内容和辅导方法(1)依照图纸、说明,或印制好的材料进行制作。(2)以培养创造能力,发展智力为中心的科技小制作。主要以制做儿童喜爱的玩具为主,有下列几种形式:①教师介绍一种小制作的方法和科学道理,并用实物演示,引起学生兴趣,学生根据这个道理自己去创新制作。如“小鸡吃米”,是利用杠杆原理制作的抽拉玩具,抽拉时两只鸡头运动方向一致或相反,是由于杠杆力点、支点的位置不同。学生在了解道理之后,各自设计、制作了许多新颖的杠杆抽拉玩具,如我坐火箭去太空、小猫钓鱼、打乒乓球、过峡谷等。②变废为宝的科技小制作。教师利用实物讲解如何利用废旧钟表的齿轮和废旧玩具设计制作新的玩具。有些学生受到启发,自己完成了构思新颖、质量较高的活动玩具,如手操纵电动旱船、电动碰碰车、机器人、滑稽人跳舞、猫头鹰和老鼠等。③专题科技制作竞赛。根据不同年级提出不同专题要求,各班学生人人设计制作,班内选拔出代表队,再进行年级竞赛。如一次四、五、六年级进行风力车比赛。我们规定赛车的轮子必须是用厚纸自制的,不能用现成轮子或其他代用品,其他大小、重量、样式不限。又一次进行橡皮筋动力车比赛,只限定必须用统一规格和长度的橡皮筋,其他不限。这样学生的积极性很高,设计制作的赛车多种多样,充分发挥了他们的聪明才智,培养了他们的创造能力。4.注意事项(1)要按年龄、知识水平、动手能力、兴趣爱好分开档次,选择不同的制作内容。低年级要选择很容易制作成功的内容,如小降落伞;中、高年级则要从难度上有所提高。(2)要提倡创新。(3)不包办代替。(4)强调制作中要注意安全
Ⅲ “杠杆原理”的英文怎么说
leverprinciple
Ⅳ 3.篇英语作文.第一篇英文作文(technology and human progress) 100words
NO.1:
1.
科学技术让人们更舒适.
2.
科学技术带来的问题.
3.
我们应该怎麽办?
Nowadays,more
and
more
hi-tech
tools,such
as
calculator,computer,etc,appear
in
our
daily
life.we
use
them
wherever
and
whenever
we
are,so
that
our
life
becomes
easier
and
more
comfortable
than
before.
However,does
anyone
think
about
what
problems
science
and
technology
have
caused
to
happen
in
this
world?To
some
degree,it's
more
serious
than
that
we
consider.We
human
indeed
use
them
to
improve
our
living
standard,but
on
the
other
hand,we
are
becoming
lazier,more
reliable
than
we
used
to
be.All
day
long
those
hi-tech
procts
accompany
us,then
we
have
either
no
space
or
time
to
think,as
well,communication
between
each
other
decreases,and
what
takes
place
of
it
is
the
huge
indifference
and
gap
among
human.
To
solve
these
problems,we
should
in
no
time
take
measures
to
do
with
them.Firstly,communicate
with
others
and
think
on
your
own
more.Secondly,decrease
the
times
you
use
hi-tech
tools.For
the
advantages
of
technology,we
should
absorb,at
the
meantime,be
independent
and
abandon
the
short-comings.Thus,we
could
combine
technology
and
human
progress
much
closer
and
not
lose
ourselves
in
this
modern
society.
Ⅳ 英文作文,Persuasive essay(400 words)
playing sports is good for our body
Ⅵ 杠杆的英文,杠杆的翻译,怎么用英语翻译杠杆,杠杆用
杠杆
[词典] lever; heaver; pry bar; gavelock; pry;
[例句]锹和耙的手柄较长,可发挥较好的杠杆作用。
The spade and fork have longer shafts, providing better leverage.
Ⅶ 物理之杠杆(英文)
moment力矩
moment=force*distance to pivot
力矩=力的大小*力与转轴之间距离
Ⅷ 10篇英语作文,全部带翻译
10篇英语小短文带翻译,稍微网络一番就有很多的范文出现。但是这些范文中,写的对不对好不好也无所得知。Ⅸ 求写一篇以loner为题的definition essay英文作文
constructing an essay which narrates an event in your life regarding a scenario where you had to intervene in a conflict, you must be sure to define the issues one may have with an intervention. As stated, one may choose not to intervene based upon how others will see him or her, fear of a physical attack or retaliation, or if it would even be right.
Given that the essay is to be read by "ecated alts," it needs to be academic in nature. The language of the essay needs to be elevated and free of slang, contractions, or grammatical errors. Since a typical narrative essay illustrates an actual event in the life of the writer, a first person point of view is appropriate.
As with any essay, one must be careful to show the importance behind the subject matter. A writer does not need to simply tell what happened. A good rule of thumb is to ask the following question: What is the point? Show. Don't tell.
You could break the essay down into three different sections defining three different situations where you address each of the situations above (one where you were worried about how others would see you; one where you were worried about your safety; one where you were not quite sure if you should intervene or not). Within each body paragraph explaining each situation, you would include what your decision was and the thought process behind it.
Another way to look at the essay could be defining one specific situation. The body paragraphs would be broken down into different "phases" of the situation: the conflict, your thoughts on the conflict, your actions regarding the conflict, and what happened based upon your decision to act or not.