mechanics力学11第二定律恒力

1、Experiment P11: Newtons Second Law Constant Force第二定律恒力(Forensor, Motion Sensor)（力传感器，移动传感器）Concept: Newtons Laws概念：定律Time: 30 mSWMacerface: 500 & 700osh_ file: P11 Constant ForceWindows_ file: P11_CONF.SWSEQUIPMENT NEEDED所需仪器Science Workshop_erfacedynamics cart动力学小车_50 Newton forensor力传感器mass set w

2、ith hanger motion sensor移动传感器 pulley with table clamp adjustable feet, track (two) stringbalance (for measuring mass)天平（用于测量质量） track, 1.2 meterr轨道，1.2mPURE目的The pure of this laboratory activity is to investigate the relationship betn force, mass, andacceleration.本实验的目的是力、质量和度之间的关系。THEORY原理Newton de

3、scribed the relationship betn acceleration, force, and mass as follows:这样描述力、质量和度之间的关系：The acceleration of an object is directly proportional to andhe same direction as the net force,and inversely proportional to the mass of the object, or一个物体的成比例且具有相同的方向，并与这个物体的质量成反比，或度与它所受的净力直接For thiivity, a moti

4、on sensor measures the motion of a cartt is pulled by a string. The ensor mounted on the cartstring is attached to a mass and suspended over a pulley. A formeasures the forcet accelerates the cart. The Science Workshop program calculates thevelocity of the moving cart. The graph of velocity versus t

5、ime reveals the carts acceleration, which is compared to the theoretical value.在这个实验中，移动传感器将测量被绳子拉动的小车的运动情况。绳子连着一个物块并悬挂在一个滑轮上。安装在小车上的一个力传感器将测量使小车显示小车的的力。Science Workshop程序将计算小车运动的速度。速度时间图表将度，并把它与理论值做比较。PART I: Computer Setup计算机设置1.将 ScienceWorkshop 接口连接到计算机上，打开接口，然后打开计算机。2.将移动传感器的声插头连接到数字通道1和2。把黄色镶边

6、的（脉头数字通道1，第二个（回声）插头数字通道2。3.将力传感器的DIN插头连接到模拟通道A。4.打开 ScienceWorkshop 如下命名的文件：1.Connect the Science Workshopthe computer.erface to the computer, turn on theerface, and turn on2.Connect the motion sensors stereo phone plugs to Digital Channels 1 and 2. Plug theyellow-banded (pulse) plug Channel 2.o Dig

7、ital Channel 1 and the second plug (echo)o Digital3.Connect the DIN plug of the forensor toog Channel A.4.Open the Science Workshop file titled as shown:Macosh: P11 Constant ForceWindows: P11_CONF.SWSThewill open wiGraph display of Velocity (m/sec) versus Time (sec), and aTable display of Force (New

8、tons).文件将打开并带有一个速度（m/s）时间（s）图表和一个表显示力（）。(Note: For quick reference, see the Experiment Notes window. To bring a display to the top,click on its window or select the name of the display from the lisof the Display. Change the Experiment Setup window by clicking on the “Zoom” box or the Restorebuttonhe

9、 upper righnd corner oft window.) 注意：如需快速参考，请参见实验注释窗口。欲将一个显示图放至前台，单击其所在窗口或从显示器底部的菜单栏中选择该显示图的名称。单击窗口右上角的扩大框或恢复按钮来改变实验设置窗口的大小。5.The “Sampling Options_” are: Periodic Samples = Fas 10000 Hz.200 Hz and Digital Timing =PART II: Sensor Calibration and Equipment Setup传感器校准和仪器设置Sensor Calibration传感器校准You do

10、 not need to calibrate the motion sensor.你无须校准移动传感器。1.To calibrate the forensor, change the Experiment Setup window to full size by clickingon the “Zoom” box or the Restore buttonhe upper righnd corner oft window.要校准力传感器，可单击实验设置窗口右上角的“Zoom”框或Restore按钮，将窗口改变至满刻度。2.he Experiment Setup window, double-c

11、lick on the forensors icon to open the ForceSensor setup window.在实验设置窗口中，双击力传感器图标来打开力传感器设置窗口。The Forensor setup window shows the default calibration values (50 Newtons produ8 Volts, -50 Newtons produ-8 Volts). The forensor is set up sot a pull awayfrom the sensor is a negative force. For example, if

12、 a one kilogram object isgvertically from the hook, the forensor measures -9.8 Newtons (since the force isdownward). 力传感器设置窗口显示了一系列缺省校准值（50产生8V，-50产生-8V）。力传感器如此设置是为了使远离传感器的力为负力。例如，如果1千克的物体被竖直悬挂在一个钩子上，力传感器的测量值将为-9.8（因为力是向下的）。3.Mount the forensor on a horizontal rod so the forensors hook is down. Do N

13、OT putan object on the for钩子朝下。还ensors hook yet.将力传感器安装在一个水平杆上，则力传感器的任何物体挂在力传感器的钩子上。4.For the “High Value” calibration po, press the tare button on the side of the forensorto zero the sensor. Click the “Read” button for “High Value”. Since there is no object onthe sensors hook, type “0” as the “High

14、 Value”. 对于“高值”校准点，按下力传感器侧面的“tare”按钮使传感器归零。对于，单击“高值”的“读数”按钮。因为没有物体挂在力传感器的钩子上，所以键入“0”作为“高值”。5.For the Low Value calibration, hang an object of known mass on the sensors hook. 对于 “低值”校准，将一个质量已知的物块挂在传感器的钩子上。6.Click the “Read” button for “Low Value”. Enter the objects weight in Newtons (mass inkilogram

15、x 9.8 N/kg). 单击“低值”的“读数”按钮。输入物体的重量，量/kg9.8N/kg）。为（质Remember, enter the objects weight as a negative value (a force pulling away from the sensor).记住：应将这个物体的重量作为负值输入（远离传感器的力）In this example, the object has a mass of 549.5 grams (0.5495 kg), or a weight of 5.385 Newtons (entered as -5.385).在这个例子中，物体的质量

16、为549.5g（0.549kg）或5.385牛顿（输入值为-5.385）。7. Click “OK” to return to the Experiment Setup window.单击“OK”返回实验设置窗口。Equipment Setup仪器设置1.Place the track on a horizontal surface. Level the track by placing the dynamics cart on the track. If the cart rolls one way or the other, use the adjustable feet at one e

17、nd of the track to raise or lower that end until the track is level and the cart will not roll one way or the other.把轨道放在水平面上。把动力学小车放在轨道上，将轨道调整至水平。如果小车只在这一条或那一条轨道上滚动，调整轨道一端的可调脚来提高或降低那一端，直到轨道处于水平位置且小车不会只在一根轨道上滚动为止。2.3Attach a pulley to the right end of the track. 把滑轮连接到轨道的右端。Position the motion senso

18、r at the left end of the track. The cart will be pulled away from the sensor. The minimum distance from the sensor to its target is 0.40 m (40 cm). Put a mark on the track 40 cm from the motion sensor.把移动传感器放在轨道的左端。小车将被拖离传感器。从传感器到它的标靶的最小距离是0.40m（40cm）。在轨道上距离移动传感器40cm的地方做一个标记。4.Use a #0 Phillips head

19、 screwdriver (available on the Force Sensor Bracket) to mount the force sensor onto the accessory tray of the cart. Carefully measure and record the total mass of the cart plus force sensor.用#0 Phillips头螺丝刀（可用于力传感器的托架）将力传感器安装在小车的附件托盘上。小心的测量小车和力传感器的总质量并记录之。5.Place the cart on the track so the hook en

20、d of the force sensor points away from the motion sensor.将小车放在轨道上，使力传感器的钩子端指向远离移动传感器的方向。Motion SensorForce SensorPulleyCartMass6.Use a string that is 10 cm longer than the length needed to reach the floor when the cart is next to the pulley. Attach one end to the force sensors hook. 将一根绳子的一头系在力传感器的钩

21、子上，绳子的长度应比小车靠近滑轮时要够到地面所需的长度长10cm。7.Add 20 or 30 grams of mass to the mass hanger. Carefully measure and record the total mass.在物块悬挂架上增加20或30g的物块。小心的测量它们的总质量并记录之。8.Attach the mass hanger to the other end of the string, and put the stringhe pulleysgroove. Adjust the height of the pulley so the string

22、is parallel to the track.把物块悬挂架 系在绳子的另一端，并把绳子放在滑轮的凹槽中。调整滑轮的高度，使绳子与轨道平行。PART IIIA: Data Recording数据1.Pull the cart toward the left end of the track but keep the carleast 40 centimeters fromthe motion sensor, and dont let the mass hanger bumpo the pulley.向轨道的左端拖动小车，但要使小车与移动传感器至少保持40cm的距离，且不要让物块架碰到滑轮。2

23、.Click the “REC” button to begin data recording and then release the cart.单击“REC”按钮开始数据，然后小车。3.Click “STOP” to end recording just before the cart reaches the pulley. 小车刚刚要够到滑轮时，单击“停止”按钮结束数据。4.Stop the cart before it collides with the pulley.小车撞到滑轮前要将它停住。“Run #1” will appearhe Data listhe Experiment

24、Setup window. Run #1将出现在实验设置窗口的数据列表中。YZING THE DATA分析数据1.Click the “Sistics” buttonhe lower left corner of the Graph display to open theSistics area. Click the “Autoscale” button to rescale the graph to fit the data.单击图表显示左下角的“统计”按钮来打开统计区。单击“自动分度按钮”来重新分度图表以适应数据。2.he plot of velocity, use the cursor

25、to click-and-draw a rectangle around the region of theplott shows the movement of the cart. 在速度曲线中，用光标单击并围绕显示小车运动的那段曲线画一个矩形。3.Click the “Sistics from the Sistics Fit, Linear Fit”。” buttonhe Sistics area. Select “Curve Fit, Linear Fit”.单击统计区中的“统计菜单”按钮。从统计菜单中选择“CurveThe Sistics area will show the y-er

26、cept (“a1”) and the slope (“a2”) for the line of bestfit for your data. The slope is the average acceleration of the cart.统计区将显示最符合你的数据的直线的y截距(“a1”)和斜率(“a2”)。斜率就是小车的平均度。You can fasten the string to the mass hanger by wrapthe string four or five turns around the notched area of the mass hanger.你可以将绳子在物块架的凹口区域缠绕4、5圈，把绳子牢牢栓在物块架上。4.Record the slope (accelera