题干

阅读材料:

做功和能置

做功在物理学中具有特定的含义.人推车时对车施加一个向前的推力,车在力的作用下前进一段距离,只有在这种情况下,物理学才认为是人对车做了功.人用的力越大,移动的距离越长,力的作用效果就越显著,人做的功就越多.

力和在力的方向上移动的距离,是做功的两个因素,缺一不可.你从地面上提起水桶时,水桶在力的作用下,向上移动了一段距离,你对水桶做了功.如果手提着水桶站着不动,虽然你用了力,但是水桶没有移动距离,你只是费了力气,没有对水桶做功,这叫“劳而无功”.这里,手提着水桶站着不动和将水桶挂在钓子上没什么两样.

做功是生产和生活中常见的现象.不仅人能做功,运动的物体也能做功.从斜面上滚下的钢球撞在木块上,能将木块推动一段距离;飞行的子弹能打穿物体,都是由于钢球和子弹克服阻力做了功的结果.

举高的物体也能做功.气锤从高处落下,能把木桩打入地下;高空落下的冰雹,由于做功而砸坏了地上的农作物.

形状变化的弹簧也能做功,钟表里被旋紧的发条慢慢地放松,带动指针嘀嘀哈哈走个不停.

一个物体能够做功,就是它具有能量.能量大的物体,做功的本领也大.风具有能量,人们就安装风车,利用风力做功.长江、黄河的水急流直下,蕴藏着很大的能量,人们筑起拦河坝,安上水轮机,让从高处落下的水推动水轮机旋转,带动发电机发电.

摘自《中国少年儿童百科全书》(浙江教育出版社)

上一题 下一题 0.0难度 选择题 更新时间:2019-04-16 07:49:35

答案(点此获取答案解析)

同类题1

阅读理解

    After spending the first five years of his life in San Diego, Adam Driver's family packet up and moved to a small town in Indiana, where Adam enjoyed a relatively routine adolescence. Then the horrific events of September 11th made Adam's life become anything but routine.

    Just a few months following the events, Driver decided to join the United States Marine Corps. He considered 9/11 as being one of the reasons for joining the army, with his desire to leave Indiana providing the rest. He once said,"I'm grateful for having grown up in Indiana, but I needed to go out and the Marine Corps was a nice, stable option." After serving for two and a half years, and just two months before he was sent to Iraq, Driver injured his sternum in a biking accident. After he was healed, he injured it again during military training, which resulted in an honorable medical discharge.

    After leaving the military, Driver decided to try his hand at acting. At first he studied close to home at the University of Indianapolis, but after just a year, he transferred to Julliard in New York City. He lived in a tiny apartment in Hoboken, New Jersey apartment while studying drama at a prestigious performing arts conservatory(音乐学院). Following his graduation in 2009, Driver immediately began appearing in plays, including 2010's Mrs. Warren's Profession.

    Adam's first major television experience was a guest spot on Law & Order, and was soon followed by a small role in the award-winning film You Don't Know Jack, which was Driver's first experience working with Home Box Office. Then after landing his star-making role on Girls, Driver was cast in a handful of feature films, including 2011's J. Edgar and 2012's Gayby, Not Waving but Drowning and Frances Ha.

    He'll appear next year in the Coen brother's Inside Llewyn Davis and Steven Spielberg's Lincoln.

根据短文内容,选择最佳答案,并将选定答案的字母标号填在题前括号内。

同类题3

      阅读下面文字,回答相关问题
      ①信息资源的传播历经语言传播时代、文字传播时代、印刷传播时代,最终过渡到电子传播时代。而互联网的出现将电子传播推向了更高层次。随着互联网发展进程的加快,网络信息资源的传播成为主流。网络信息资源的传播与传统信息资源的传播相比,呈现出新的特点。
      ②首先,网络信息资源传播的途径具有多样性。网络信息资源传播的途径有很多,网上论坛作为网络组织传播途径,为群体成员之间进行信息资源的传播和交流提供了方便;而网站作为网络大众传播途径,则成为个人、组织及国家机构发布信息的主要平台;微博为个人发布信息提供了捷径。同时,一些新兴的信息传播途径正走进人们的视线,像贴吧、微信等。另外,无论是电子邮件、还是QQ等,都是互联网上人与人之间进行信息资源传播的常用方法。
       ③其次,网络信息资源传播的内容具有丰富性。当前人们的关注点十分广泛,过去以单一形态传播的信息资源已无法满足人们广泛的兴趣爱好,但网络信息资源却能突破传统限制。网络信息资源借助多种传播形态,如文本、图像、音频、视频、软件、数据库等,将各领域资源和各种文件类型在互联网上传播。网络信息资源涉及的领域可以从经济、科研、教育、艺术、娱乐等再到具体的行业和个体,包含的文件类型可以是电子报刊、电子工具书、商业信息、新闻报道、书目数据库和文献信息索引,也可以是统计数据、图表、电子地图等。网络信息资源可谓应有尽有,这些都尽可能地满足了人们不同的需求。
      ④再次,网络信息资源传播的速度具有___性。在网络媒体上,我们往往看不到头版头条新闻在哪儿,新闻内容总在不断滚动更新。借助数码摄录设备和手机等现代化影像处理及通讯工具,网络新闻记者可以进行事件的现场直播,在网络上图文并茂地以第一时间、第一速度把事件报道出来,特别是对突发事件的报道,网络比电视编辑的时间更短暂,更迅速。在网络上公众可以看到事件每分钟的发展情况,而网络后台的编辑们还可以迅速调出与事件相关的背景图文资料,让社会公众更全面更客观地了解事件真相、新闻后面的故事或细节。
      ⑤网络信息资源的传播改变了广大民众获取信息、传播信息的方法和渠道,使人类突破了时空的约束,步入了自由的王国,不仅拉近了人们的距离,也丰富了人们的见识。