高中物理人教版 (新课标)必修14 实验：用打点计时器测速度导学案

这是一份高中物理人教版 (新课标)必修14 实验：用打点计时器测速度导学案，共3页。学案主要包含了实验原理，实验器材，实验步骤，数据处理，注意事项和误差分析等内容，欢迎下载使用。
一、实验原理1．两种打点计时器(电磁打点计时器和电火花计时器)在接通50 Hz的交流电源时，打点时间间隔都是0.02 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2．当纸带跟运动物体连在一起时，打点计时器打在纸带上的点就相应地表示出物体在不同时刻的位置，纸带上各点之间的间隔就表示相应时间间隔中物体的位移，根据平均速度的定义式＝，当Δt很短时，可以认为等于t时刻的瞬时速度．二、实验器材打点计时器(电磁打点计时器或电火花计时器)、纸带、刻度尺、交流电源、导线等．两种打点计时器的比较： 电磁打点计时器电火花计时器电源种类6V以下低压交流电源220 V交流电源打点频率打点时间间隔0.02 s、频率50Hz打点时间间隔0.02 s、频率50Hz打点方式振针通过复写纸在纸带上打点火花放电使墨粉在纸带上成点阻力来源纸带与限位孔的摩擦；振针与纸带打点接触时的摩擦纸带与限位孔的摩擦；摩擦阻力比电磁打点计时器小电火花计时器比电磁打点计时器更精确，实验误差小。三、实验步骤1．把电磁打点计时器固定在桌子上，让纸带穿过限位孔，压在复写纸的下面．2．把电磁打点计时器的两个接线柱用导线分别与电源的接线柱相连接．3．打开电源开关，用手水平地拉动纸带使它在水平方向上运动，纸带上就打下了一系列点．4．关闭电源，取下纸带，从能看得清的某个点数起，数一数纸带上共有多少个点，如果共有n个点，那么点的间隔数为n－1个，纸带的运动时间Δt＝0.02(n－1) s.5．用刻度尺测量出从开始计数的点到最后的点间的距离Δx.6．利用公式＝，计算出纸带在这段时间内的平均速度． 7．从几条纸带中选择一条比较理想的纸带,舍掉开始一些比较密集的点,在后面便于测量的地方找一个开始点,以后依次每五个点取一个计数点,并标明A、B、C、D…，如图所示，测出O到A、A到B、B到C…之间的距离x1、x2、x3…. 四、数据处理1．表格法打点计时器打点的周期为T，则A、B、C、D…各点的瞬时速度分别为：vA＝、vB＝、vC＝，vD＝…把数据填入下表，根据数据判断纸带是否做匀速运动。位置编号123456(Xn+Xn+1)/m      v/(m/s)      2．图象法(1)图象的描绘：以速度v为纵轴、时间t为横轴，在方格纸上建立直角坐标系．根据测得的速度值在坐标系中描点，然后用平滑的曲线将这些点连接起来，就得到了一条能够描述纸带运动的速度v与时间t关系的图象．称为速度—时间图象，简称速度图象，即v-t图象．(2)v-t图象的意义v-t图象非常直观地反映了速度随时间变化的情况，它并不是物体运动的轨迹．(3)v-t图象中反映的物理量①任一时刻瞬时速度的大小。②速度的方向。速度为正，表示物体沿规定的正方向运动，速度为负，表示物体沿规定的正方向的反方向运动．③从v-t图象上可以直观的看出速度随时间的变化情况④匀速直线运动的图象是一条平行于t轴的直线五、注意事项和误差分析（略）二、典例分析：题型一、打点计时器的原理及使用例1、电磁打点计时器是一种使用___________电源的计时仪器，它的工作电压为________，当电源频率为50 Hz时，它每隔________s打一次点．使用电磁打点计时器时，应将纸带穿过______，复写纸套在定位轴上，并要放在纸带的________面；应把__________电源用导线接在接线柱上；打点时应先________，再让纸带运动．题型二、纸带的测量、分析和计算例2、 如图所示为某次实验时打出的纸带，打点计时器每隔0.02 s打一个点，图中O点为第一个点，A、B、C、D为每隔一点选定的计数点．根据图中标出的数据，纸带上A、C两点对应的时间为______s，纸带在A、D间的平均速度为______cm/s，打B点时纸带的瞬时速度为______cm/s，你能求出打O、D点时间内纸带的平均速度吗？为什么？答：____  ______  _____.变式练习：打点计时器所用电源的频率为50 Hz，某次实验中得到的一条纸带，用毫米刻度尺测量情况如图145所示，纸带在A、C间的平均速度为________m/s，在A、D间的平均速度为________m/s，B点的瞬时速度更接近于________m/s.