推荐回答(4个)
1、写一写你对一个物理现象的观察,或过程、或提问、猜想、假设,可以没有结论,也可以有结论,要依据你的生活经验或已有的知识
写。要用心观察,用脑思考。力的、光的、声的等等都可以。
2、描述你对一个问题的思考。
3、写一写你上过的一节物理课。
4、写一写你听说过的与物理有关的事物,可以以对话形式写。
物理类论文大体上分成这样几个部分
1.背景介绍。(交代历史背景已经前人相关研究结果)
2.基础理论。(文中具体用到什么样的物理知识,注意,是基本理论)
3.模型与计算(本文中具体采用了什么样的设计方法,得到了什么养的计算数据,图表。等等)
4.结论与展望(写改论文的目的以及研究结论,本文中有什么创新点,今后在这个基础上还可以继续做什么样的文章)
1.两类力做功的特点:
重力(电场力)做功只与初、末位置有关,与运动的路径无关;如滑动摩擦力做功与运动的路径有关,且当力的大小保持不变时做功等于力的大小与路程的乘积。
2.摩擦力做功的特点:
在静摩擦力做功的过程中,只有机械能的相互转移,静摩擦力起着传递机械能的作用,而没有机械能转化为其他形式的能。相互摩擦的系统内,一对静摩擦力所做功的和总是为零。一对滑动摩擦力做功的过程中,能量的转化有两个方面:一是相互摩擦的物体之间机械能的转移,二是机械能转化为内能,转化为内能的量值等于滑动摩擦力与相对位移的乘积,一对滑动摩擦力所做功的和为负值,其绝对值等于系统损失的机械能。
3.机械能是否守恒的判断:
从做功来判断:分析物体或物体系受力情况(包括内力和外力),明确各力做功的情况,若对物体或系统只有重力或弹力做功,没有其他力做功,则机械能守恒。
从能量转化来判断:若物体或物体系中只有动能和重力势能、弹性势能的相互转化而无机械能与其他形式的能的转化,则物体或物体系机械能守恒。如绳子突然绷紧、物体间碰撞贴合等现象时,机械能不守恒。
4.功能关系
各个力所做的总功等于物体动能的变化;重力做功等于重力势能变化量的负值;弹簧弹力做功等于弹性势能变化量的负值;除了重力和弹簧弹力以外其他力所做的功等于物体机械能的变化。
【例】如图所示,跨过同一高度处的定滑轮的细线连接着质量相同的物体A和B,A套在光滑水平杆上,定滑轮离水平杆的高度h=0.2m,开始时让连着A的细线与水平杆的夹角θ1
=
37°,由静止释放B,当细线与水平杆的夹角θ2
=
53°时,A的速度为多大?在以后的运动过程中,A所获得的最大速度为多大?(设B不会碰到水平杆,sin37°
=
0.6,sin53°
=
0.8,取g
=
10m/s2)
【解析】对A、B两物体组成的系统,只有动能和重力势能的相互转化,机械能守恒。设绳与水平杆夹角θ2=53°时,A的速度为υA,B的速度为υB,此过程中B下降的高度为h1,则有:
mgh1=■mv2A+■mv2B,
其中h1=■-■,
A、B两物体沿绳方向速度相等即:υAcosθ1
=
υB
代入数据,解以上关系式得:υA=
1.1m/s
A沿着杆滑到左侧滑轮正下方的过程,绳子拉力对A做正功,A做加速运动,此后绳子拉力对A做负功,A做减速运动。故当θ3
=
90°时,A的速度最大,设为υAm,此时B下降到最低点,B的速度为零,此过程中B下降的高度为h2,则有:mgh2
=■mυ2Am
,其中h2
=■-h代入数据解得:υAm
=
1.63m/s。
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