物理代寫 - APHY 145 Lab 2

時間：2020-10-12

APHY 145 Lab 2(F2020)Linear motion1Linear motionSummaryUsing the data fromthe motion sensor(Fig. 1),make plots of positionandvelocity as functions of time, and compare different ways of calculatingvelocity. TheoryFor one-dimensional motion in a straight line, the displacementΔ??is the net distance traveled during a specified time interval:Δ??=???????0,(1)where ??0is the starting location,and ????is the final location. The average velocityvis ??=Δ??Δ??=???????0???????0,(2)where ?tis the elapsed time.For a constant velocity v,the final position is??=??0+??Δ??.If the velocity is not constant, there is non-zero acceleration. The average accelerationahasthe same relationship to velocity as velocity has to displacement:??=Δ??Δ??=???????0???????0.(3)ReferenceSerway & Jewett,“Physics for Scientists and Engineers,”Chapter 2.Color key for online labsTheonlineversions of APHY 145labs are based on the in-person versions and may retain most of the originallab instructions,regardless of whether youareperformingthe actual experiment.Green text highlights commentary to help you understand the lab or how to write your report.Blue text highlights key steps of the lab process that you should read carefully.Red text highlights steps important to recording data inExcel data sheet.Online vs. in-personForthis experiment,the data has already been collected; yourtask is tocarefully analyze it.EquipmentLinear motion sensorLabPro interfaceNote: sonic ranger motion detectorThe motion detector emits short bursts of ultrasonic sound waves.Each burst is accompanied by a clicking sound from the detector. The computer calculates the distance from the time it takes an echo to Figure 1. Motion sensor.
APHY 145 Lab 2(F2020)Linear motion2return to the detector. The sound waves emitted from the detector fill a cone of about 20?, as shown inFig.2. Stationary objects (stools, tables, lab partners) within that cone will cause echoes that interfere with the reading.The range of the detector is 0.5 -2 m. Objectscloser than 0.5 m or farther than 2 m away may not be detected.Procedure1.SET UPPurpose: totest that the detector does not getinterferencefrom nearby sources.The motion detector should be plugged into the LabPro interfaceattached to the computer. Open the “Experiments”folder on the desktop,and click on thefile“LinearMotion.” Placethe motion detectoron the edge of a table. Standingabout1 m away from the detector, click “Collect.” After5 seconds, move to the point 2 maway.Verify that the graph of position vs.time displayed on the computer screen shows you starting at 1 m and ending at 2 m. Troubleshooting: occasionally the Logger Pro software cannot find the detector.Make sure everything is connected and powered, and restartthe software.2.WALKING AWAYSLOWLYPurpose: to produce constant velocitydataand calculateaverage velocity in three different ways.2.1 Position vs. time dataStandingabout 0.5 m from the detector,click “Collect,” and walk slowly and steadily, at a constant velocity,away from the detector. Your graph of position as a function of time should be close to a straight line. Practice a few times until it does.2.2 Average velocity:manual slope calculationUsingScreenshot 1(at the end of thismanual),read the time and position for the three pairs of data points:at9sand 1s, 8sand 2s, and 7sand 3s.Inthis step, use the orange dots(datapoints),not the black fit line.Do your best to read the plot as accuratelyas possible.Record thesemeasurements in an Excel spreadsheet.Calculate the change in position and time for eachpair of points,and find velocityv(slope) for each pairusing Eq.2.Calculate the average velocity and its uncertainty (standard error)for all three trials. The standard errorfor ntrials is ??????????????=??/√??, where σis the standard deviation of the set.2.3Average velocity:linear fitAnother way to find the velocity is to fit the position vs. time curve to a straight line. Select arelatively straight portionof thedataand use the Curve fittingiconto find the slope and its uncertainty.To fit a line, select “y=mt+b”. Click on “try fit,” then “Ok”. A box with the intercept, slope anduncertaintieswill appear.Read the average velocity and its uncertainty from the Linear Fitbox shown in Screenshot 1.Record the results in your spreadsheet.detectorSound wavescone20?Object being measured?Figure 2. Sonic ranger motion detector.
APHY 145 Lab 2(F2020)Linear motion32.4Average velocity: velocityvs.time plotChange the graph to plot velocity vs.time. Click on the word “Position” on the y-axis. After amenu appears, select “Velocity” from the list. Select the linear portion of thetime range and deploythe Statistics tool.Using the information provided in the Statisticsboxin Screenshot 2, determine the average (mean) velocity and its uncertainty (standard error).Record your results.Change the graphback to position vs.time.3.WALKING AWAYQUICKLYPurpose: to compare the graphs for high and low velocity data.3.1 Position vs. time dataRepeat Section 0,but walk faster.3.2 Average velocityScreenshot 3employsoneof the methodsfrom Section 2 tofind the average velocity and its uncertaintyfor the new data set.Record both the method and the measured valuein Excel.4.WALKING FORWARDPurpose: to compare the graphs for positive and negative velocity data.4.1 DataRepeat Section 0,but start 2 m from the detector and walk towards it (either fast or slow).4.2 Average velocityScreenshot 4employsoneof the methodsfrom Section 2 tofind the average velocity and its uncertaintyfor the new data set.Record both the method and the measured valuein Excel.Lab Report Questions1. What arethe average velocities calculated in Section 2 by threedifferent methods? Do theyagree with each other within uncertainty? Which methoddo you judge themost precise, and why?If you have calculated uncertainties for a particular value, always report them as part of your results.Values agreewithin uncertaintyif there is an overlap between theirranges.2. Compare the slopes of the graphsin Sections 2and3of the lab: which one is greater?Do the values make sense based on the type of motion observed in theseexperiments?Answer labquestions in complete sentences.3. Compare the slopes of the graphsin Sections 2and 4 of the lab: which one is greater?Do the values make sense based on the type of motion observed in each experiment?Remember that a negative value is smaller than a positive one.Lab reports (including Excel data sheets) should be submitted via Blackboard and have due dates listed on Blackboard.Use the data provided belowto create your Excel sheet and labreport.
APHY 145 Lab 2(F2020)Linear motion4LAB DATA (provided asscreenshots of LabPro interface)Screenshot 1(Sections 2.2and 2.3)Screenshot 2(Section 2.4)
APHY 145 Lab 2(F2020)Linear motion5Screenshot 3(Section 3)Screenshot 4(Section 4)

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