friction force on the rack

Friction and Lubrication
摩擦和润滑
In many of the problems thus far, the student has been asked to disregard or neglect friction.
到目前为止,在许多问题的处理中,学生都被告知不计入摩擦力或者忽略摩擦力.
Actually, friction is present to some degree whenever two parts are in contact and move on each other.
实际上,当两部分接触并且相对运动时,总要产生一定程度的摩擦.
The term friction refers to the resistance of two or more parts to movement.
边界摩擦力取决于两个或者多个部分相对运动时相互之间的阻碍程度.
Friction is harmful or valuable depending upon where it occurs.
根据产生时所处的位置不同,摩擦力可以是有害的也可以是有益的.
Friction is necessary for fastening devices such as screws and rivers which depend upon friction to hold the fastener and the parts together.
摩擦力在锁紧装置中是必须存在的,比如螺旋副和rivers,这些装置依靠摩擦力保持锁紧状态并且使各部分连接起来.
Belt drivers, brakes, and tires are additional applications where friction is necessary.
带传动、制动器、轮胎都是必需摩擦力的应用例子.
The friction of moving parts in a machine is harmful because it reduces the mechanical advantage of the device.
机器中运动部件产生的摩擦力是有害的,因为它会降低装置的机械效率.
The heat produced by friction is lost energy because no work takes place.
摩擦产生的热量又损失了能量,因为它没有做功.
Also, greater power is required to overcome the increased friction.
另外,需要大量的能量来克服增长的摩擦力.
Heat is destructive in that it causes expansion.
热量引起的膨胀变形是具有破坏性的.
Expansion may cause a bearing or sliding surface to fit tighter.
热膨胀可能使轴承或者滑动表面更紧.
If a great enough pressure builds up because of expansion, the bearings may seize or freeze.
当热膨胀引起的压力变的足够大时,轴承可能停止运动甚至是烧结.
In addition, as heat is developed, bearings made from low temperature materials may melt.
另外,随着热量的增加,由低温工作用材料制成的轴承可能会熔化.
There are three types of friction which must be overcome in moving parts:
运动的物体中存在三种类型的必须克服的摩擦力：
(1)starting, (2)sliding, and(3)rolling.
1、静摩擦力,2、滑动摩擦力,3、滚动摩擦力
Starting friction is the friction between two solids that tend to resist movement.
静摩擦力是在两个相互限制对方运动的物体之间产生的摩擦力.
When two parts are at a state of rest, the surface irregularities of both parts tend to interlock and form a wedging action.
当两部分在静止状态时,两表面的不规则形状使它们产生互相锁紧并且产生楔形作用.
To produce motion in these parts, the wedge-shaped peaks and valleys of the stationary surfaces must be made to slide out and over each other.
在两部分产生运动的过程中,静止表面的楔形的尖端和凹处必然与另以表面相互滑进滑出.
The rougher the two surfaces, the greater is the starting friction resulting from their movement.
两表面越粗糙,由它们引起的静摩擦力就越大.
Since there is usually no fixed pattern between the peaks and valleys of two parts, the irregularities do not interlock once the parts are in motion but slide over each other.
由于通常两配合面的尖端和凹处没有固定的形状,一旦发生相对的运动不规则表面将不再互锁.
The friction of the two moving parts is known as sliding friction.
两运动表面间的摩擦被称作滑动摩擦.
As shown in Fingure1,starting friction is always greater than sliding friction.
如图1中所示,静摩擦力总是比滑动摩擦力大.
Rolling friction occurs when roller devices are subjected to tremendous stresses which cause the parts to change shape or deform.
滚动摩擦力产生在受到引起部件形变的巨大压力的滚动装置上.
Under these conditions, the material in front of a roller tends to pile up and forces the object to roll slightly uphill.
在这种情况下,滚动件的前部的材料产生堆积并且产生使物体向相反方向滚动的力.
This changing of shape, known as deformation, causes a movement of molecules.
这种被看作弹性变形的形状的改变,引起了分子之间的相对运动.
As a result, heat is produced from the added energy required to keep the parts turning and overcome friction.
结果,需要额外的能量来保持部件的转动并且克服摩擦力,并由此产生的热量.
The friction caused by the wedging action of surface irregularities can be overcome partly by the precision machining of the surfaces.
由不规则表面的楔形作用引起的摩擦力,能够部分的通过机器的表面精度被克服.
However, even these smooth surfaces may require the use of a substance between them to reduce the friction still more.
然而,即使这种光滑的表面也仍然需要在表面之间填充一些一些物质来降低摩擦.
This substance is usually a lubricant which provides a fine, thin oil film.
这种物质通常是能产生一层精细而且薄的油膜的润滑剂.
The film keeps the surfaces apart and prevents the cohesive forces of the surfaces from coming in close contact and producing heat.
这层薄膜保持两表面分离并且通过紧密的接触和产生的热量提供黏着力.
问题补充：Another way to reduce friction is to use different materials for the bearing surfaces and rotating parts.
另一种降低摩擦的方式是使用不同的材料来制作轴承的表面和滚动部件.
This explains why bronze bearings, soft alloys, and copper and in oilite bearings are used with both soft and hardened steel shafts.
这便解释了为何青铜、软合金和紫铜用在与软表面或者硬表面钢轴配合的自润滑轴承中.
The oilite bearing is porous. Thus, when the bearing is dipped in oil, capillary action carries the oil through the spaces of the bearing.
自润滑轴承是多孔状的.应此,当轴承浸入油中时,油会通过毛细作用充满轴承中的小孔.
This type of bearing carries its own lubricant to the points where the pressures are the greatest.
这种类型的轴承能把它自身存储的润滑油释放在压力最大的位置.
Moving parts are lubricated to reduce friction, wear, and heat.
对运动部件的润滑能够降低摩擦、磨损和生成的热量.
The most commonly used lubricants are oils, greases, and graphite compounds.
最常用的润滑剂是油、脂、以及石墨复合物.
Each lubricant serves a different purpose.
不同的润滑剂使用在不同的条件下.
The conditions under which two moving surfaces are to work determine the type of lubricant to be used and the system selected for distributing the lubricant.
两运动表面的工作情况决定系统的润滑方式和布油方式.
On slow moving parts with a minimum of pressure, an oil groove is usually sufficient to distribute the required quantity of lubricant to the surfaces moving on each other.
低速轻载运动的部件,一个润滑油槽通常就能够为相对运动表面提供足够的润滑.

这个ON的意思是你要给接触面定义摩擦力,在你定义接触力的对话框中展开所有选项,你将看到关于摩擦力的选项,你可以按照你上面给出的选项填入相应选项即可.

选A,不可以选B的原因：1、were的主语必须要是复数.no friction 的后面的be动词只可以是单数形式.2、were there 在句首的时候,就是疑问句了,那后面必须有疑问号,但是上面的句子句尾是句号.这说明不是疑问句.
选A的话,if就是表示假设,有如果、假如的意思.根据这句话,它所表达的是假设的意思.所以四个选项中只有A最合适.

If we need to supply friction shims identical to mass production parts,we need to get an order for a stamping tool and an order for at least one production batch (12,000 pcs) as stated in our offer 1367-MS8874 of March 31,2010.
如果我们需要提供与主生产零件相匹配的摩擦夹板,我们需要得到一份一个压模工具的订单和一份至少一个生产单位（一万二千件）的订单,正如我们在2010年3月10日所提供的 1367-MS8874.
For the various prototype and pre-production stages we usually offer lower quantities of laser-cut parts.The coating process and the functionality of these parts is identical to the mass production parts,only the base part is produced with laser cutting instead of stamping.Laser cutting is more expensive for the individual part,but does not require investment for a stamping tool.
由于不同的样板和预生产阶段,我们通常提供较少量的激光切割零件.涂层过程和这些零件的功能性和主生产零件相匹配,只有底部零件是由激光切割代替压模.激光切割对于单独零件来说更昂贵,但不需要投资一个压模工具.
If you can give us an indication about the required quantity of prototype parts,we will send you a quotation.
如果你可以给我们一个关于需求的样板零件数量的指示,我们将会给发给你一个报价.

were not able to改为would not be able to

螺纹紧固件的摩擦系数应按照DIN 946标准进行测试/检验,但以下（情况）除外：

DIN 946 应该是一种技术标准（德国标准）.

with the following exceptions 就是以下情况除外的意思,在你的文章中一定下面还有内容,描述几种除外的情况.不能翻译成别的.
per DIN 946 是按照DIN 046标准.

3.答案应为 B.这是一个虚拟条件句,并且省略if 后,用倒装形式.
下面一句答案应为A.that 从句应填虚拟语气,用 should +v 原形,此处省略 should.这两个题都是利用省略做文章,虚拟 和省略健儿有之.

friction:摩擦, 摩擦力, 分歧
e.g. My daughter and son always have frictions.
conflict:冲突, 战斗, 矛盾, 斗争
e.g.If so, your points of view are bound to conflict with his.
摩擦和冲突之间差别很大
好比战斗和战役,规模大小把握一下就好
friction累积矛盾能成为conflict

摩擦面的除锈方向应该与其所受压力的方向垂直

这个就是静摩擦与动摩擦.主要先说的是,如果你推一个很沉的箱子,你会发现你很难让箱子移动.静摩擦就是使箱子静止的力.如果你轻轻推箱子,静摩擦力就很小,用力推箱子,静摩擦力就很大.当然,这是有一个界限的的.当你作用在箱子上的力大于最大静摩擦力,那么箱子就被你推动了.
然后就是在解释公式……F=μN 求动摩擦.N是支持力,F是摩擦力,μ是摩擦系数.剩下的你就自己百度去吧……

由于摩擦而浪费了大量能量

中子不带电
物体不带电时 是指物体中带正电的质子数等于带负电的电子数 所以整体不带电
两个原本不带电的物体相互摩擦 电子发生转移 质子和中子数不会发生变化
对于得到电子的物体 电子数大于质子数 所以带负电
对于失去电子的物体 电子数小于质子数 所以带正电
举个例子 甲物体 2个质子 2个电子 4个中子
乙物体 3个质子 3个电子 8个中子
它们的质子数等于电子数 总体都不带电
假设相互摩擦后 一个电子从甲跑到了乙上
那么甲质子数就比电子数多了一个 总体带一个正电荷
乙电子数比质子数多一个 总体带一个负电荷
所以摩擦起点后 两个原本不带电的物体 带上等量异种电荷 整个过程与中子无关

是A B 还是 B of A,确实挺纠结的.个人认为如果着重于一个整体词汇,A B 比较好,如果着重于B,则B of A 较好.例如本例,把空气阻力作为一个整体词汇对待,air friction 较好,如果着重于阻力,则用 friction of air 较好.总之区别不大.在实际应用中,为了减少of的使用频率,以及简化句子,往往会用A B多一些.

两个物体质量分别为：M,m.（M>m）通过绳子连接跨过定滑轮,滑轮重量和摩擦力不计,求物体M的加速度.
解法1、 把两个物体看做一个整体.
a=（M-m）g/(M+m)
解法2、设绳子的拉力为：F
则有对M,F=Mg-Ma
对m由：F=mg+ma
故：Mg-Ma=mg+ma
化简：a=（M-m）g/(M+m)

潜打印
Although the word latent means hidden or invisible,in modern usage for forensic science the term latent prints means any chance of accidental impression left by friction ridge skin on a surface,regardless of whether it is visible or invisible at the time of deposition.虽然这个词潜在的或无形的手段隐藏在法医学长期潜伏版画现代用法,是指：通过摩擦脊皮肤表面留下的印象意外的机会,不论它是可见或不可见的沉积时间.
Electronic,chemical and physical processing techniques permit visualization of invisible latent print residue whether they are from natural secretions of the eccrine glands present on friction ridge skin (which produce palmar sweat,consisting primarily of water with various salts and organic compounds in solution),or whether the impression is in a contaminant such as motor oil,blood,paint,ink,etc.电子,化学和物理处理技术,允许残留的可视化无形的潜在打印是否从山脊上的摩擦皮肤（手掌出汗而产生,主要是与各种盐溶液中的有机物和水组成）目前汗腺腺体分泌物自然,或是否在污染物的印象是,如机油,血液,油漆,油墨等
Latent prints may exhibit only a small portion of the surface of the finger and may be smudged,distorted,overlapping,or any combination,depending on how they were deposited.潜伏打印可能会出现只有手指的表面的一小部分,可能是污迹,扭曲,重叠,或任意组合,这取决于他们如何存放.
For these reasons,latent prints are an “inevitable source of error in making comparisons,” as they generally “contain less clarity,less content,and less undistorted information than a fingerprint taken under controlled conditions,and much,much less detail compared to the actual patterns of ridges and grooves of a finger.”由于这些原因,潜在的版画是“不可避免的误差来源进行比较,”因为他们一般“含有较少的清晰,内容较少,而较少失真比在受控条件下采取了指纹信息,以及更多,更详细的比较,脊和沟槽的手指实际模式.

第一问：a1=gsinΘ-u1gcosΘ=4.134;a2=gsinΘ-u2gcosΘ=3.268;
第二问：分两种情况,因为第一个箱子的加速度大,迟早会追上2号箱子；在追上之前,加速度和第一问一样,追上后,两个箱子挨在一起,考虑为一个整体；于是有：a1=a2=【(m1+m2)sinΘ-u1m1gcosΘ-u2m2gcosΘ】/（m1+m2）=3.557;
第三问中：一号箱子在下,绳子始终是绷直的,于是就可以将两个箱子考虑为一个整体和第二问中两个箱子挨在一起是一样的,加速度为：3.557.

计算合力吧?平行四边形法则啊,将两个力分解即可.

确实都会出现啊.
根据泊松方程的变体TV^γ-1=定值,体积减小气体温度就睡上升.
而气体和液体之间的主要区别是分子间距的问题,当分子间距被急剧压缩到很小的时候自然就会液化.
不过很显然液化的条件是比较多的,而不管什么时候绝热压缩温度一定上升.
具体这里指哪一个.SAT2的题其实通常不是很严谨.估计应该是前者吧,毕竟这个更普遍一些.

1. 这首诗很平稳畅顺地,把对象从自然转向人,更优雅地把山、树、鸟和徜徉其间的一切都融合在一起；它的音韵天衣无缝地从元音 u 转成 du ('thou') 和 Ruh ('rest'),让人有一种受抚慰和受保护的感觉,更进而令人感到,纵...

我物理不是特别好 但是翻译一下应该还是可以的 有些词你自己再把握下 我尽量哦~
一个放置在没有摩擦力桌面上的水平弹簧,于其不能拉伸的形态（应该就是说此时是保持静止放置的状态）被拉伸了17厘米,并附带一个1千克的块体.这个系统被释放的瞬间,弹簧由静止状态被压缩了3.4厘米
它的最终势能与最初势能相比发生了怎样的变化（按最后到最初的比率给出你的答案）

相关表观摩擦角?
对机械不熟悉,应该不是力而是个角度吧

电机轴承：无摩擦

The friction is the only force to provide the centripetal force,the bigger the force is,the faster the car can travel around.The maximum force is
F=f=μmg.(1),where F is the centripetal force,μ is the coefficient of friction.
The centripetal force F=mv^2/R.(2),where R is 80m,
we can get v=17.9m/s^2 （if g=10m/s^2）