雨滴所受阻力与速度一次方成正比吗?

有一本《理论力学简明教程》在讨论阻力与速度|v|的一次方成正比时指出:从高空落下的雨滴正是由于空气阻力使其收尾速度只有4—6米/秒(随雨滴大小而异),所以雨滴打不坏庄稼。言外之意,下落雨滴所受空气阻力与速度的一次方成正比。其实,这种说法是不对的。我们知道,雨滴尺度(直径)约自0.2 mm至7 mm,再小就不易降到地面,再大则在降落过程中因受微小的气流脉动等外力作用而容易破碎。由于雨滴为球形,从高空落下后,当     

智能雨滴传感系统设计

智能雨滴传感系统由雨滴传感器和控制电路两部分组成.利用光线在不同介质中的折射,设计一种V型槽式结构的雨滴接受系统,使得传感器在接收到雨滴后,引起光线的偏折,从而感应雨滴.实验证明,该雨滴传感系统灵敏度高,性能稳定,无延迟.     

雨滴真的匀速下落吗?

有这样一道题:“无风的时候竖直下落的雨滴受到两个力的作用:重力,空气阻力。设空气阻力F与雨滴下落的速度v成正比,即F=kv。开始下落时雨滴的速度较小,空气的阻力也较小,雨滴加速下落,速度越来越大。随着速度的增大,空气阻力也增大。当空气阻力增大到与重力平衡时,雨滴就以一定的速度匀速下落。这个速度叫做极限速度或收尾速度。设雨滴的质量为m,试证明雨滴的极限速度v=mg/k。”     

勤劳的小雨滴

春天到了,小雨滴忙开了。小雨滴来到山坡,挥着神奇的小银锄播种。不久,山坡上长出绿油油的嫩草。小雨滴来到花园,挥着     

雨滴下落问题刍议

通过对雨滴下落机理的探讨,揭示了雨滴下落的本质,排除了雨滴是因“空气的浮力托不住才落向地面”的误解,并解答了有关雨滴下落问题的一些疑惑.     

天上的淘气包

天上有一群淘气包。想到地上来走一遭,就使劲地器鼻子,变成了小雨滴,脚跟脚地往地上跑。逛到大街上的小雨滴。“滴答滴答”地拍手跳,跳得石头唱着快乐的童谣。它不停地笑,笑得小树伸出了嫩嫩的小手,挺直了腰。飘到花丛中的小雨滴,见到小草,小草向它挥挥手,弯弯腰;见到小花,小花向它点点头,哈哈笑。落到草原上的小雨滴很淘气很淘气,马儿向它微微笑,虫儿向它点点头。跃进池塘里的小雨滴很快乐很快乐,乐得鲤鱼跳龙门,水草扭扭腰。     

前景诱人的气象能

雨能科学家对雨滴进行了长期的观察、研究,发现它具有巨大的能量。过去曾测出的最大雨滴直径为0,75厘米。最近,科学家又在美国的加利福尼亚地区发现迄今为止世界上最大的雨滴,其直径为1,0厘米。假如这一雨滴是在地面以上高40米的空中出现,又假定它下降时是按重力加速度的     

小雨滴的故事

我是小雨滴。我从天上落下来,掉到一片叶子上睡着了,清晨的风吹醒了我,我决定去找水妈妈。于是,我出发了。路上,我碰到了小河姐姐,我高兴地说:“小河姐姐,我一个人孤零零的。让我到你的怀抱中去吧?”小河姐姐连连摇头,说:“小雨滴,人们不注意保     

生活中的物理

一、为什么在下雨的地方彩虹呈弧形而不是彩色的一片？当光线进入雨滴,从雨滴出来就形成彩虹。光线的路径弯曲的大小取决于它所通过的物质以及波长,也就是光的颜色。所以当太阳光进入雨滴时,它所包含的不同光线的弯曲程度是不同的：红色最小,紫色的最大。因此从雨滴里显现出来的是各种颜色,每一种颜色的弧度大约都在40～42度之间。每一滴被太阳光照着的雨滴都会发生这种的情况,但是我们只能在某些雨滴中看到彩虹,它们的弧度是40～42度,     

雨滴有时轻 有时重

雨滴到瘫有多轻落在桃利上轻轻为桃树抹了一点点口红雨浦到底有多重落在大海里 ‘大海就波浪翻腾雨墒到底有多小落在土地上再也看不见它的身影雨滴到底有多大落在森枇里 ’所有的绿,÷都睁开了春天的眼睛 (摘自《人民日报》)雨滴有时轻 有时重@张俊以     

Error analysis of non-spherical raindrops on precipitation measurement

Radar cross section (RCS) of non-spherical raindrops is calculated by using the software CST based on finite integral method and compared with RCS of spherical raindrops. The revised factor of non-spherical raindrops is obtained. The radar reflectivity with precipitation change of four distribution models of M-P, Gamma, JD and JT combining the revised factor is gotten using trapezoidal integration. When the influence of non-spherical raindrops is considered, the accuracy of precipitation measurement of four distribution models can be separately improved 8.77%, 8.47%, 10.53% and 8.04% in the case of rain intensity is 100 mm/h.     

蛙声、雨点兆丰年--解读辛弃疾《西江月》的"蛙声一片"和"两三点雨"

在《西江月·夜行黄沙道中》这首词中 ,词人对那“说丰年”的一片蛙声和山前的“两三点雨”的描写 ,不仅仅是一种想象和写实 ,它还间接揭示了农业丰收的两个重要条件 :青蛙和雨水。只有了解这两个条件的重要性 ,才能更好地理解这首词轻快活泼的抒情基调 ,才能真正理解作者对农业丰收在望的喜悦心情     

雨滴下落的数值模拟

对变质量雨滴的下落过程进行了研究,建立下落雨滴的动力学方程,用理论推导求解析解,并用计算机编程求解数值解,结果表明理论分析与数值结果一致。     

Lotus-inspired nanotechnology applications

The water-repellent surface of lotus (Nelumbo nucifera) leaf and flower is due to nanosized wax papillae on the upper side of each epidermal cell. As a result, raindrops make a high contact angle with the papillae and roll off carrying dust and dirt particles, leaving the surface clean. This self-cleaning property of highly hydrophobic surfaces, termed as the lotus effect, has opened the possibilities of fabricating superhydrophobic surfaces for a variety of products.     

本期话题：多元语境中的话语场——文艺复兴时期关于亚里士多德《修辞学》的论争：传播理论的跨文化解读

本演讲探讨了欧洲早期艺复兴期间（大约1350—1700）为解读亚里士多德的（修辞学）中的论述所做出的努力,讨论了欧洲的注释在理解亚里士多德的（修辞学〉中所遇到的困难,关注了当时学意料之外的某些论争,并力图阐释引起这些论争的原因。作认为,人们力图阐释关于一种化的论述并力图从另一种化的需求和兴趣来解读这种论述的努力对中美两国具有重要意义,这些阐释所可能引发的结果也具有积极意义。作的这种解读对当今世界——对中国和“西方”国家富有更为广泛的意义——因为他在试图解读产生于一种化而被转译到另一种化的修辞学和传播学理论。作指出,在欧洲艺复兴时期,人们相信修辞学和社会很大程度上是一回事。修辞学能够使人们避免暴力、摆脱兽性,使许多不同人的思想统一起来,促成一种包容各种矛盾的和谐社会。修辞学使我们变得明。[第一段]     

文艺复兴时期关于亚里士多德《修辞学》的论争:传播理论的跨文化解读

本演讲探讨了欧洲早期文艺复兴期间(大约1350-1700)为解读亚里士多德的《修辞学》中的论述所做出的努力,讨论了欧洲的注释者在理解亚里士多德的《修辞学》中所遇到的困难,关注了当时学者意料之外的某些论争,并力图阐释引起这些论争的原因。作者认为,人们力图阐释关于一种文化的论述并力图从另一种文化的需求和兴趣来解读这种论述的努力对中美两国具有重要意义,这些阐释所可能引发的结果也具有积极意义。作者的这种解读对当今世界——对中国和“西方”国家富有更为广泛的意义——因为他在试图解读产生于一种文化而被转译到另一种文化的修辞学和传播学理论。作者指出,在欧洲文艺复兴时期,人们相信修辞学和社会很大程度上是一回事。修辞学能够使人们避免暴力、摆脱兽性,使许多不同人的思想统一起来,促成一种包容各种矛盾的和谐社会。修辞学使我们变得文明。     

Critical literacy: Beyond reason

In this paper, I argue that critical literacy is essentially a rationalist activity that does not sufficiently address the non-rational investments that readers bring with them to texts and tasks. I begin by looking at playful advertising texts that work with humour and the transgressive in order to consider the role of pleasure rather than reason. Then I examine the force of powerful identifications in relation to reason to show that educational interventions cannot ignore them. Finally, I tentatively suggest that we may need to find ways to combine socio-cultural and psycho-analytic theory in order to imagine new directions for pedagogy in the critical literacy classroom.     

Countering the ‘new orthodoxy’ in educational research: a response to Phil Hodkinson

In a previous article, Phil Hodkinson argued that there are currently attempts to impose a methodological orthodoxy on educational research, one that is empiricist in character and privileges quantitative method. While agreeing with much of what he says, I take issue with key elements of his argument. I suggest that he presents too rosy a picture of the existing state of educational research, question his apparent advocacy of a laissez‐faire approach to its governance, and argue that he underplays the significant role that methodological rules can play in shaping the practice of research in desirable ways. I suggest that his approach is likely to reinforce paradigmatic fragmentation in the research community, and that this weakens any attempt to resist the internal and external pressures that currently threaten to damage or destroy educational research in the UK, and elsewhere.     

Leaping Out of Our Skins: Postmodern considerations in use of an electronic whiteboard to foster critical engagement in early literacy lessons

Postmodern theory is used to consider literacy instruction with and without an electronic whiteboard to investigate what it means to move beyond using technology to replicate older models of classroom structure that may be historically situated but that also limit or at least, do not support engagement in ways that may be possible through use of new technologies. Using postmodern theory in this regard is a way in which to consider again the thoughts and practices that tend to construct identities and ideologies in ways that work against true engagement in literacy tasks, lead to subjection and demonstration of acquiescence in place of engagement that leads to participation and critical engagement. Critical engagement as opposed to gaining and maintaining student attention to task are considered in this paper. Thinking about use of the electronic whiteboard from a postmodern perspective cautions us about careful use of this technology to avoid sending messages to students about them and their role in literacy development, the classroom, and in society.