1、Unit 8 General ScienceWork and PowerWork and Power功和功率功和功率*功表示力和受力物体在力的作用功表示力和受力物体在力的作用方向上发生的位移的乘积。方向上发生的位移的乘积。*功率表示力做功的快慢程度。功率表示力做功的快慢程度。TWW=F*SP=Fast readingFast readingRead the text quickly and answer the following questions.1.What is the definition of 1.What is the definition of“workwork”?”?2.Ho
2、w do you calculate the amount 2.How do you calculate the amount of work done?of work done?3.What is the definition of 1 3.What is the definition of 1 joulejoule?4.What is the definition of 4.What is the definition of“powerpower”?”?5.What is the definition of 15.What is the definition of 1wattwatt?Wo
3、rk is done when a force Work is done when a force causes an object to move or causes an object to move or prevents it from moving.prevents it from moving.the definition of the definition of“work”:“work”:Equation:W=FEquation:W=F*S S Work done=force Work done=force X X distance distance moved in the d
4、irection of the moved in the direction of the force force Work done equals force times Work done equals force times distance moved in the distance moved in the direction of the force.direction of the force.ExampleExampleAn athlete applies a force of 2000 An athlete applies a force of 2000 newtons to
5、 move up the weights to newtons to move up the weights to the height of 2 meters.How much the height of 2 meters.How much work has the athlete done?work has the athlete done?2000N2000N2m2mWork doneWork done =2000N X=2000N X 2m2m=4000J=4000J1 joule1 jouleIf a force of 1 N causes an If a force of 1 N
6、causes an object to move 1 meter,then object to move 1 meter,then 1J of work has been done.1J of work has been done.1N1mThe definition of“power”The definition of“power”Power is a measure of how Power is a measure of how rapidly work is being done.rapidly work is being done.Power=Power=timetakenworkd
7、one1watt1wattIf a person or a machine is If a person or a machine is doing 1J of work each doing 1J of work each second,the power rating is 1 second,the power rating is 1 W.W.ExampleExampleGo on looking at the athlete,if Go on looking at the athlete,if the work takes the athlete the work takes the a
8、thlete 0.5second to lift the weights 0.5second to lift the weights above his head,what is the power above his head,what is the power of the athlete?of the athlete?Power=Power=sJ5.04000=8000Wor 8Kw=8000Wor 8KwSum upSum upWork ;work done;1 Joule;power;Work ;work done;1 Joule;power;1Watt.1Watt.Work don
9、e=2000N X 2m=4000JWork done=2000N X 2m=4000JPower=4000J Power=4000J 0.5s=8000w or 8kw0.5s=8000w or 8kwHomeworkHomeworkThe lawnmower move needs 80 The lawnmower move needs 80 newtons,its engine can newtons,its engine can apply 50 newtons.A lady apply 50 newtons.A lady pushed the lawnmower along pushe
10、d the lawnmower along a straights line for 40 a straights line for 40 meters.How much work has meters.How much work has the lady done?the lady done?编后语 同学们在听课的过程中，还要善于抓住各种课程的特点，运用相应的方法去听，这样才能达到最佳的学习效果。一、听理科课重在理解基本概念和规律 数、理、化是逻辑性很强的学科，前面的知识没学懂，后面的学习就很难继续进行。因此，掌握基本概念是学习的关键。上课时要抓好概念的理解，同时，大家要开动脑筋，思考老师是
11、怎样提出问题、分析问题、解决问题的，要边听边想。为讲明一个定理，推出一个公式，老师讲解顺序是怎样的，为什么这么安排？两个例题之间又有什么相同点和不同之处？特别要从中学习理科思维的方法，如观察、比较、分析、综合、归纳、演绎等。作为实验科学的物理、化学和生物，就要特别重视实验和观察，并在获得感性知识的基础上，进一步通过思考来掌握科学的概念和规律，等等。二、听文科课要注重在理解中记忆 文科多以记忆为主，比如政治，要注意哪些是观点，哪些是事例，哪些是用观点解释社会现象。听历史课时，首先要弄清楚本节教材的主要观点，然后，弄清教材为了说明这一观点引用了哪些史实，这些史料涉及的时间、地点、人物、事件。最后，也是关键的一环，看你是否真正弄懂观点与史料间的关系。最好还能进一步思索：这些史料能不能充分说明观点？是否还可以补充新的史料？有无相反的史料证明原观点不正确。三、听英语课要注重实践 英语课老师往往讲得不太多，在大部分的时间里，进行的师生之间、学生之间的大量语言实践练习。因此，要上好英语课，就应积极参加语言实践活动，珍惜课堂上的每一个练习机会。2023-1-11最新中小学教学课件15thank you!2023-1-11最新中小学教学课件16
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