上海交通大学：《物理实验》精品课程教学资源（讲义）2 Free Falling Body

2.Free-falling Body Aim: 1.Study the motion of free-falling body. 2.Determine local gravity acceleration 3.Grasps the principle and application of computer assistance in data acquisition and analyzing. 4.Learn and understand how to used Vedeocom camera to measure object's movement Operational Principle: The Videocom camera is specially designed with connections to computers.Vedeocom helps to acquire data for computers through a single track CCD.This device can record object's linear movement with high accuracy. To record the motion of an object,reflection foil must be pasted to the object.LED shines light to the foil and Videocom camera detects the reflected light.Based on the difference from background light,the camera is able to determine the position of the foil.In this experiment, Videocom camera measures the position and movement of the object.Then one can determine the velocity,acceleration and other quantities of movement. Before doing the experiment,calibration of the system must be performed.That is to say,one has to determine the relationship between pixel difference and position distance.And one can make it that object's one meter of position movement corresponds to 4000 standards movement of the object's image on the screen. Linearization can further improve the measurement's accuracy.The method is to detect reflected light from two foils placed on the free-falling object and then use software to automatically calculate a correction value for the position difference.Recalibration is needed after linearization. Fig.I displays the experimental setup.The quantity measured is S(t)but the displayed ones are v(t)and a(t).One can calculate and display any quantities based on his/her interest from the formula tab.For example:E(t)=0.5mv12+mg(h-sl)is the mechanical energy of the free- falling body and from E(t)one can understand the variation of mechanical energy during its falling. Other Candidate Topics: 1.Study the law of motion for free-falling body 2.Determine locality's gravity acceleration 3.Estimate the impact of air resistance on the measurement. 4

4 2. Free-falling Body Aim: 1. Study the motion of free-falling body. 2. Determine local gravity acceleration 3. Grasps the principle and application of computer assistance in data acquisition and analyzing. 4. Learn and understand how to used Vedeocom camera to measure object’s movement Operational Principle: The Videocom camera is specially designed with connections to computers. Vedeocom helps to acquire data for computers through a single track CCD. This device can record object’s linear movement with high accuracy. To record the motion of an object, reflection foil must be pasted to the object. LED shines light to the foil and Videocom camera detects the reflected light. Based on the difference from background light, the camera is able to determine the position of the foil. In this experiment, Videocom camera measures the position and movement of the object. Then one can determine the velocity, acceleration and other quantities of movement. Before doing the experiment, calibration of the system must be performed. That is to say, one has to determine the relationship between pixel difference and position distance. And one can make it that object’s one meter of position movement corresponds to 4000 standards movement of the object’s image on the screen. Linearization can further improve the measurement’s accuracy. The method is to detect reflected light from two foils placed on the free-falling object and then use software to automatically calculate a correction value for the position difference. Recalibration is needed after linearization. Fig.1 displays the experimental setup. The quantity measured is S(t) but the displayed ones are v(t) and a(t). One can calculate and display any quantities based on his/her interest from the formula tab. For example: E(t) = 0.5mv1 2 +mg(h-s1) is the mechanical energy of the free￾falling body and from E(t) one can understand the variation of mechanical energy during its falling. Other Candidate Topics: 1． Study the law of motion for free-falling body 2． Determine locality's gravity acceleration 3． Estimate the impact of air resistance on the measurement

Instruments: Videocom camera,33747:Camera tripod,30059:Electromagnet,33621:Power support (12 Volts),526791:supporter,33621:Iron (free-falling body),337472:wire: computer assistance system for data acquisition and calculation. :京510t5网 Fig.1:Experimental Setup Instructions(step by step): 1.Understanding of the general requirements of the experiment and the basic process by reading available references. 2.Read the instructions of instruments to be used in the experiment. 3.Connect the computer,click the Videocom icon to open the software.Read the help files and introduction to free-fall experiments. 4.Calibrate the system: (1)Place the camera to the position with 2 times height the free-falling body. (2)Make the camera vertical to ground with the help of level meter. (3)Attach the iron to the Electromagnet on top of the supporter.Adjust the potentiometer on top of the supporter and make the iron about to fall. (4)Adjust the system so that the two reflectors can be displayed clearly. (5)Adjust the position of the camera so that the two images are located at the position of 0.0m and 2.0m 5.Open existing files in the folder C:\Data,understand the setup of experimental parameters and display ofexperimental data. 6.Create a personal folder under the path of C:\StuData named by your ID number.Save the experiment number in to your personal folder.Create a text file named with the your name to record information of the experiment

5 Instruments: Videocom camera，33747 ；Camera tripod，30059；Electromagnet，33621；Power support (12 Volts)，526791；supporter，33621；Iron（free-falling body），337472；wire； computer assistance system for data acquisition and calculation. Fig.1: Experimental Setup Instructions (step by step): 1. Understanding of the general requirements of the experiment and the basic process by reading available references. 2. Read the instructions of instruments to be used in the experiment. 3. Connect the computer, click the Videocom icon to open the software. Read the help files and introduction to free-fall experiments. 4. Calibrate the system： (1) Place the camera to the position with 2 times height the free-falling body. (2) Make the camera vertical to ground with the help of level meter. (3) Attach the iron to the Electromagnet on top of the supporter. Adjust the potentiometer on top of the supporter and make the iron about to fall. (4) Adjust the system so that the two reflectors can be displayed clearly. (5) Adjust the position of the camera so that the two images are located at the position of 0.0m and 2.0m 5. Open existing files in the folder C:\Data, understand the setup of experimental parameters and display of experimental data. 6. Create a personal folder under the path of C:\StuData named by your ID number. Save the experiment number in to your personal folder. Create a text file named with the your name to record information of the experiment

7.Select the Settings icon,set the experimental parameters. ☒ ba色o8回6N 9, 000 1=92 00 300 Setting/Totk Colikysties 原习 的可 5egnd习 C AEedi Pahs.m Carcel yLEYBOLD ODACTIC GmH 1987-2000 Fig.2:Parameter Setup 8.Finish the tasks listed or think of some by yourselves.Put the experimental number into your personal folder. 9.Copy your folder with a floppy disk,analyze the data and finish a report of the experiment Warnings: 1.Please read the instructions carefully before using any equipment. 2.Please keep the shot of CCD and camera clean. 3.Please format the floppy disk for data transfer before experiment Questions: 1.State the operational principle of Videocom camera. 2.State the impact of At on experimental accuracy. 3.Estimate the impact of Vedeocom camera's position on the measurements. 4.Discuss the advantage and disadvantage of computer assistance on data acquisition and analyzing 5.Think about the problems you meet with during the experiment and make some hypotheses.Try to make it quantitatively and verify it through experiment. 6.Try to describe the principle of Linearization and verify your understanding through the experiment. 6

6 7. Select the Settings icon，set the experimental parameters. Fig.2: Parameter Setup 8. Finish the tasks listed or think of some by yourselves. Put the experimental number into your personal folder. 9. Copy your folder with a floppy disk, analyze the data and finish a report of the experiment Warnings: 1. Please read the instructions carefully before using any equipment. 2. Please keep the shot of CCD and camera clean. 3. Please format the floppy disk for data transfer before experiment Questions: 1. State the operational principle of Videocom camera. 2. State the impact of ∆t on experimental accuracy. 3. Estimate the impact of Vedeocom camera’s position on the measurements. 4. Discuss the advantage and disadvantage of computer assistance on data acquisition and analyzing. 5. Think about the problems you meet with during the experiment and make some hypotheses. Try to make it quantitatively and verify it through experiment. 6. Try to describe the principle of Linearization and verify your understanding through the experiment