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1、八年级下册物理知识点汇总八年级下册物理知识点汇总(人教版新教材) 登封市直二初中 王晓红 第七章 力 第一节 力 1( 力的概念:力是物体对物体的作用。符号:F 2(力的单位:国际单位制中力的单位是牛顿简称牛，用N表示。 力的感性认识:拿两个鸡蛋所用的力大约1N。 3(力产生的条件:?必须有两个或两个以上的物体;?物体间必须有相互作用(可以不接触)。 4(力的作用效果:力可以改变物体的运动状态;力可以改变物体的形状。 说明:物体的运动状态是否改变一般指:物体的运动快慢是否改变(速度大小的改变)和物体的运动方向是否改变。 5(力的三要素:力的大小、方向、和作用点。 6(力的表示法:力的示意图:用
2、一根带箭头的线段把力的大小、方向、作用点表示出来，如果没有大小，可不表示，在同一个图中，力越大，线段应越长。 7(力的性质:物体间力的作用是相互的(相互作用力在任何情况下都是大小相等，方向相反，作用在不同物体上)。两物体相互作用时，施力物体同时也是受力物体，反之，受力物体同时也是施力物体。 第二节 弹力 1.弹性:在受力时会发生形变，不受力时，又恢复到原来的形状，物体的这种性质叫做弹性。 2.塑性:形变后不能自动地恢复到原来的形状，物体的这种性质叫做塑性。 3.弹力:物体由于发生弹性形变而产生的力叫做弹力。 4.压力、支持力都是弹力。 5(力的测量: ?测力计:测量力的大小的工具。 loan
3、management (post) review: 1, approval criteria have been implemented; 2, the contract is correct; 3, in line with the contract, payment; 4, no other major cases against loan security;、Reviewed by: date of record form 9: qilu bank borrowing by single years of maximum amount a maximum no-loan borrower
4、s: borrowers: . Borrower name number, line of credit expiry date year month day to year month day maximum number of years in the loan contract are the top line opened, the borrowed and requested your bank opened credit lines above, is hereby requested. Borrower signature: date agreed to open credit
5、lines. Customer Manager signature: date agreed to open credit lines. Loan review signature: date line cancellation-I did not use the loan amount, your bank credit lines to be cancelled. -Credit loan principal repayment, your bank credit lines to be cancelled. Borrower signature: date-unused credit l
6、ines, agree to write off loans. -Credit loan principal repayment, agree to write off loans. Customer Manager signature: date case, agree to write off loans. Loan review signature: date of record form 16: qilu self credit for credit card cancellation application form name of borrower ID number and cr
7、edit limit expiration date year month day to year month day year contract number self-service card-I do not use credit, your bank credit lines to be cancelled. -Credit loan principal repayment, your bank credit lines to be cancelled. Borrower signature: date-unused credit lines, agree to write off l
8、oans. -Credit loan principal repayment, agree to write off loans. Customer Manager signature: ?分类:弹簧测力计、握力计。 ?弹簧测力计: A、原理:在弹性限度内，弹簧的伸长与所受的拉力成正比。 B、使用方法: “看”:量程、分度值、指针是否指零; “调”:调零; “读”:读数=挂钩受力。 C、注意事项:加在弹簧测力计上的力不许超过它的最大量程。 D、物理实验中，有些物理量的大小是不宜直接观察的，但它变化时引起其他物理量的变化却容易观察，用容易观察的量显示不宜观察的量，是制作测量仪器的一种思路。这种科
9、学方法称做“转换法”。利用这种方法制作的仪器:温度计、弹簧测力计、压强计等。 第三节 重力 1.重力:由于地球的吸引而使物体受到的力叫做重力，通常用字母G表示。 地球附近的所有物体都受到重力的作用。 物体所受的重力跟它的质量成正比。 2.重力的大小:G = mg g = 9.8N/kg g的物理意义:质量是1kg的物体受到的重力是9.8N。 3.重力的方向:竖直向下 铅垂线(重垂线)的原理:重力的方向竖直向下 4.重心:重力的作用点 5.找重心的方法: A.形状规则、质量分布均匀的物体，它的重心在它的几何中心上。 B.悬挂法找重心 6.万有引力: 第八章 运动和力 loan managemen
10、t (post) review: 1, approval criteria have been implemented; 2, the contract is correct; 3, in line with the contract, payment; 4, no other major cases against loan security;、Reviewed by: date of record form 9: qilu bank borrowing by single years of maximum amount a maximum no-loan borrowers: borrow
11、ers: . Borrower name number, line of credit expiry date year month day to year month day maximum number of years in the loan contract are the top line opened, the borrowed and requested your bank opened credit lines above, is hereby requested. Borrower signature: date agreed to open credit lines. Cu
12、stomer Manager signature: date agreed to open credit lines. Loan review signature: date line cancellation-I did not use the loan amount, your bank credit lines to be cancelled. -Credit loan principal repayment, your bank credit lines to be cancelled. Borrower signature: date-unused credit lines, agr
13、ee to write off loans. -Credit loan principal repayment, agree to write off loans. Customer Manager signature: date case, agree to write off loans. Loan review signature: date of record form 16: qilu self credit for credit card cancellation application form name of borrower ID number and credit limi
14、t expiration date year month day to year month day year contract number self-service card-I do not use credit, your bank credit lines to be cancelled. -Credit loan principal repayment, your bank credit lines to be cancelled. Borrower signature: date-unused credit lines, agree to write off loans. -Cr
15、edit loan principal repayment, agree to write off loans. Customer Manager signature: 第一节 牛顿第一定律 1(伽利略斜面实验: ?三次实验小车都从斜面顶端滑下的目的是:保证小车开始沿着平面运动的速度相同。 ?实验得出得结论:在同样条件下，平面越光滑，小车前进地越远。 ?伽利略的推论是:在理想情况下，如果表面绝对光滑，物体将以恒定不变的速度永远运动下去。 ?伽利略斜面实验的卓越之处不是实验本身，而是实验所使用的独特方法?在实验的基础上，进行理想化推理。(也称作理想化实验)它标志着物理学的真正开端。 2(牛顿第一
16、定律: ?牛顿总结了伽利略、笛卡儿等人的研究成果，得出了牛顿第一定律，其内容是:一切物体在没有受到力的作用时，总保持静止状态或匀速直线运动状态。 ?说明: A、牛顿第一定律是在大量经验事实的基础上，通过进一步推理而概括出来的，且经受住了实践的检验所以已成为大家公认的力学基本定律之一。但是，我们周围不受力是不可能的，因此不可能用实验来直接证明牛顿第一定律。 B、牛顿第一定律的内涵:物体不受力，原来静止的物体将保持静止状态，原来运动的物体，不管原来做什么运动，物体都将做匀速直线运动。 C、牛顿第一定律告诉我们:物体做匀速直线运动可以不需要力，即力与运动状态无关，所以力不是产生或维持运动的原因。力是
17、改变物体运动状态的原因。 3(惯性: ?定义:物体保持运动状态不变的性质叫惯性。 ?说明:惯性是物体的一种属性。一切物体在任何情况下都有惯性，惯性大小只与物体的质量有关，与物体是否受力、受力大小、是否运动、运动速度等皆无关。 4(惯性与惯性定律的区别: A、牛顿第一定律也称为惯性定律 B、惯性是物体本身的一种属性，而惯性定律是物体不受力时遵循的运动规律。 C、任何物体在任何情况下都有惯性，(即不管物体受不受力、受平衡力还是非平衡力)，loan management (post) review: 1, approval criteria have been implemented; 2, the
18、 contract is correct; 3, in line with the contract, payment; 4, no other major cases against loan security;、Reviewed by: date of record form 9: qilu bank borrowing by single years of maximum amount a maximum no-loan borrowers: borrowers: . Borrower name number, line of credit expiry date year month
19、day to year month day maximum number of years in the loan contract are the top line opened, the borrowed and requested your bank opened credit lines above, is hereby requested. Borrower signature: date agreed to open credit lines. Customer Manager signature: date agreed to open credit lines. Loan re
20、view signature: date line cancellation-I did not use the loan amount, your bank credit lines to be cancelled. -Credit loan principal repayment, your bank credit lines to be cancelled. Borrower signature: date-unused credit lines, agree to write off loans. -Credit loan principal repayment, agree to w
21、rite off loans. Customer Manager signature: date case, agree to write off loans. Loan review signature: date of record form 16: qilu self credit for credit card cancellation application form name of borrower ID number and credit limit expiration date year month day to year month day year contract nu
22、mber self-service card-I do not use credit, your bank credit lines to be cancelled. -Credit loan principal repayment, your bank credit lines to be cancelled. Borrower signature: date-unused credit lines, agree to write off loans. -Credit loan principal repayment, agree to write off loans. Customer M
23、anager signature: 物体受非平衡力时，惯性表现为“阻碍”运动状态的变化;惯性定律成立是有条件的。 ?人们有时要利用惯性，有时要防止惯性带来的危害，请就以上两点各举两例(不要求解释)。 答:利用:跳远运动员的助跑;用力可以将石头甩出很远;骑自行车蹬几下后可以让它滑行。防止:小型客车前排乘客要系安全带;车辆行使要保持距离;包装玻璃制品要垫上很厚的泡沫塑料。 第二节 二力平衡 1(定义:物体在受到两个力的作用时，如果保持静止状态或匀速直线运动状态称二力平衡。 2(二力平衡条件:二力作用在同一物体上、大小相等、方向相反、两个力在一条直线上。 (同物、等大、反向、共线) 概括:二力平衡条
24、件用四字概括“一、等、反、一”。 物体在二力平衡下，可以静止，也可以作匀速直线运动。 物体的平衡状态是指物体处于静止或匀速直线运动状态。处于平衡状态的物体所受外力的合力为零。 3(平衡力与相互作用力比较: 相同点:?大小相等;?方向相反;?作用在一条直线上不同点:平衡力作用在一个物体上可以是不同性质的力;相互力作用在不同物体上是相同性质的力。 4(力和运动状态的关系: 物体受力条件 物体运动状态 说明 力不是产生(维持)运动的原因 受非平衡力 力是改变物体运动状态的原因 合力不为0 5(应用:应用二力平衡条件解题要画出物体受力示意图。 loan management (post) review
25、: 1, approval criteria have been implemented; 2, the contract is correct; 3, in line with the contract, payment; 4, no other major cases against loan security;、Reviewed by: date of record form 9: qilu bank borrowing by single years of maximum amount a maximum no-loan borrowers: borrowers: . Borrower
26、 name number, line of credit expiry date year month day to year month day maximum number of years in the loan contract are the top line opened, the borrowed and requested your bank opened credit lines above, is hereby requested. Borrower signature: date agreed to open credit lines. Customer Manager
27、signature: date agreed to open credit lines. Loan review signature: date line cancellation-I did not use the loan amount, your bank credit lines to be cancelled. -Credit loan principal repayment, your bank credit lines to be cancelled. Borrower signature: date-unused credit lines, agree to write off
28、 loans. -Credit loan principal repayment, agree to write off loans. Customer Manager signature: date case, agree to write off loans. Loan review signature: date of record form 16: qilu self credit for credit card cancellation application form name of borrower ID number and credit limit expiration da
29、te year month day to year month day year contract number self-service card-I do not use credit, your bank credit lines to be cancelled. -Credit loan principal repayment, your bank credit lines to be cancelled. Borrower signature: date-unused credit lines, agree to write off loans. -Credit loan princ
30、ipal repayment, agree to write off loans. Customer Manager signature: 画图时注意:?先画重力然后看物体与那些物体接触，就可能受到这些物体的作用力;?画图时还要考虑物体运动状态。 第三节 摩擦力 1. 定义:两个互相接触的物体，当它们发生相对运动或有相对运动趋势时，就会在接触面上产生一种阻碍相对运动的力，这种力就叫做摩擦力。 2. 滑动摩擦力的大小与接触面所受的压力有关，接触面受到的压力越大，滑动摩擦力越大;滑动摩擦力的大小还与接触面的粗糙程度有关，接触面越粗糙，滑动摩擦力越大。 3. 摩擦的利用与防止: 利用:走路时穿带花纹
31、的鞋底;自行车把做成螺纹状;传送皮带上上皮带蜡;雪天路面铺灰渣。 防止:机器上的轴承装珠子，并上些润滑油;在地上拉重物时在物体下面放上圆木棍，车陷入泥地在上面铺上木板 第九章 压强 第一节 压强 一、压强 ?压强p:物体所受压力的大小与受力面积之比叫做压强。 压力F:垂直作用在物体表面上的力，单位:牛(N)。 压力产生的效果用压强大小表示，跟压力大小、受力面积大小有关。 2 压强单位:N/m，读作:牛每平方米; 专用名称:帕斯卡，简称帕，符号:Pa 2公式: p=F/S 【S:受力面积，两物体接触的公共部分;单位:m。】 2.改变压强大小方法:?减小压力或增大受力面积，可以减小压强;?增大压力
32、或减小受力面积，可以增大压强。 第二节 液体的压强: loan management (post) review: 1, approval criteria have been implemented; 2, the contract is correct; 3, in line with the contract, payment; 4, no other major cases against loan security;、Reviewed by: date of record form 9: qilu bank borrowing by single years of maximum a
33、mount a maximum no-loan borrowers: borrowers: . Borrower name number, line of credit expiry date year month day to year month day maximum number of years in the loan contract are the top line opened, the borrowed and requested your bank opened credit lines above, is hereby requested. Borrower signat
34、ure: date agreed to open credit lines. Customer Manager signature: date agreed to open credit lines. Loan review signature: date line cancellation-I did not use the loan amount, your bank credit lines to be cancelled. -Credit loan principal repayment, your bank credit lines to be cancelled. Borrower
35、 signature: date-unused credit lines, agree to write off loans. -Credit loan principal repayment, agree to write off loans. Customer Manager signature: date case, agree to write off loans. Loan review signature: date of record form 16: qilu self credit for credit card cancellation application form n
36、ame of borrower ID number and credit limit expiration date year month day to year month day year contract number self-service card-I do not use credit, your bank credit lines to be cancelled. -Credit loan principal repayment, your bank credit lines to be cancelled. Borrower signature: date-unused cr
37、edit lines, agree to write off loans. -Credit loan principal repayment, agree to write off loans. Customer Manager signature: 1.产生原因:由于液体有重力，对容器底产生压强;由于液体流动性，对器壁产生压强。 2.规律:?同一深度处，各个方向上压强大小相等?深度越大，压强也越大?不同液体同一深度处，液体密度大的，压强也大。 深度h，液面到液体某点的竖直高度。 3.公式:p=gh h:单位:米; :千克,米3; g=9.8牛,千克。 4.测量工具:液体压强计(U型管压强计)
38、。 5.连通器:上端开口、下端连通的容器。 6.连通器原理:连通器里装的是相同的液体，当液体不流动时，连通器各部分中的液面高度总是相同的。 第三节 大气压强 1.大气受到重力作用产生压强，证明大气压存在且很大的是马德堡半球实验，测定大气压强数值的是托里拆利(意大利科学家)。托里拆利管倾斜后，水银柱高度不变，长度变长。 2. 1个标准大气压,76厘米水银柱高,1.01105帕,10.336米水柱高 3.测定大气压的仪器:气压计(水银气压计、盒式气压计)。 4.大气压强随高度变化规律:海拔越高，气压越小，即随高度增加而减小，沸点也降低。 第四节 流体压强与流速的关系 在气体和液体中，流速越大的位置
39、，压强越小。 第十章 浮力 1、浮力的定义:一切浸入液体(气体)的物体都受到液体,气体,对它竖直向上的力 叫浮力。 2、浮力方向:竖直向上，施力物体:液,气,体 3、浮力产生的原因(实质):液(气)体对物体向上的压力大于向下的压力，向上、向下的压力差 即浮力。 4、物体的浮沉条件: loan management (post) review: 1, approval criteria have been implemented; 2, the contract is correct; 3, in line with the contract, payment; 4, no other majo
40、r cases against loan security;、Reviewed by: date of record form 9: qilu bank borrowing by single years of maximum amount a maximum no-loan borrowers: borrowers: . Borrower name number, line of credit expiry date year month day to year month day maximum number of years in the loan contract are the to
41、p line opened, the borrowed and requested your bank opened credit lines above, is hereby requested. Borrower signature: date agreed to open credit lines. Customer Manager signature: date agreed to open credit lines. Loan review signature: date line cancellation-I did not use the loan amount, your ba
42、nk credit lines to be cancelled. -Credit loan principal repayment, your bank credit lines to be cancelled. Borrower signature: date-unused credit lines, agree to write off loans. -Credit loan principal repayment, agree to write off loans. Customer Manager signature: date case, agree to write off loa
43、ns. Loan review signature: date of record form 16: qilu self credit for credit card cancellation application form name of borrower ID number and credit limit expiration date year month day to year month day year contract number self-service card-I do not use credit, your bank credit lines to be canc
44、elled. -Credit loan principal repayment, your bank credit lines to be cancelled. Borrower signature: date-unused credit lines, agree to write off loans. -Credit loan principal repayment, agree to write off loans. Customer Manager signature: (1)前提条件:物体浸没在液体中，且只受浮力和重力。 (2) 物体的浮沉条件: F浮 F浮 F浮 F浮 G G G G
45、 下沉 悬浮 上浮 漂浮 F G F= G 浮 浮 浮 浮 液物液物液物液物(3)、说明: ? 密度均匀的物体悬浮,或漂浮,在某液体中，若把物体切成大小不等的两块，则大块、小块都悬浮,或漂浮,。 ?一物体漂浮在密度为的液体中，若露出体积为物体总体积的1/3，则物体密度为(2/3) F浮 分析:F= G 则:Vg =Vg 浮 液排物2 =( V,V)?= 物排液液3G ? 悬浮与漂浮的比较 相同: F= G 浮 不同:悬浮 =;V=V 液物 排物漂浮 ;VV 液物排物?判断物体浮沉(状态)有两种方法:比较F与G或比较与 。 浮 液物? 物体吊在测力计上，在空中重力为G,浸在密度为的液体中，示数为
46、F则物体密度为:= G/ (G-F) 物?冰或冰中含有木块、蜡块、等密度小于水的物体，冰化为水后液面不变，冰中含有铁块、石块等密大于水的物体，冰化为水后液面下降。 5、阿基米德原理: (1)、内容:浸入液体里的物体受到向上的浮力浮力的大小等于它排开的液体受到的重力。 (2)、公式表示:F= G =Vg 从公式中可以看出:液体对物体的浮力与液体的密度浮 排液排和物体排开液体的体积有关，而与物体的质量、体积、重力、形状 、浸没的深度等均无关。 (3)、适用条件:液体,或气体, 6(漂浮问题“五规律”: 规律一:物体漂浮在液体中，所受的浮力等于它受的重力; 规律二:同一物体在不同液体里漂浮，所受浮力
47、相同; loan management (post) review: 1, approval criteria have been implemented; 2, the contract is correct; 3, in line with the contract, payment; 4, no other major cases against loan security;、Reviewed by: date of record form 9: qilu bank borrowing by single years of maximum amount a maximum no-loan
48、 borrowers: borrowers: . Borrower name number, line of credit expiry date year month day to year month day maximum number of years in the loan contract are the top line opened, the borrowed and requested your bank opened credit lines above, is hereby requested. Borrower signature: date agreed to open credit lines. Customer Manager signature: date agreed to open credit lines. Loan review signature: date line cancellation-I did not use the loan amount, your bank credit lines to be cancelled. -Credit loan principal r