L124. Turntable Physics

Occasionally, we give you a problem that requires laboratory-type skills of analysis to solve but for which the data is generated from an animation or other source as opposed to coming from real-world measurements. Some situations in which we use generated data are ones where we're either unable to provide you either with hands-on equipment or with video/images of hands-on equipment in use. Such is the case for the present assignment. You'll collect data from an animation, and then you'll apply graphical analysis techniques to determine an unknown. In order to provide somewhat of a real-world feel to the data, some uncertainty in the value of the dependent variable is introduced into the animation. Thus, when you do the graphical analysis, the data points will show some scatter about the line as they would in the real world.

 Introduction

  1. Watch the video:  Force and Acceleration on a Turntable - Part I:  Streamed / RealPlayer / Flash.

  2. Next open this applet. (Ignore the Seed Number input for now.) This animation models the same situation as in the Force and Acceleration on a Turntable video. When you play the applet, you'll see the coin slide off the turntable when the turntable reaches a particular frequency. You can change the radius to see how that influences the maximum frequency at which the coin can continue to move in a circular path.

 Goals

  1. Demonstrate the skills of graphical analysis that you've acquired this semester. See the Summary of Graphical Analysis Experiences to review.

  2. Determine the coefficient of static friction between the turntable and the coin by a) measuring the frequency at which the coin first slips as a function of the radius of the circular path and b) performing a graphical analysis. The following method of analysis must be used: Re-express the independent variable in order to obtain a linear relationship between the relevant variables. Then, through a comparison of the fit results to the theory of the situation, determine the coefficient of static friction.

 Prelab

Submit WebAssign L124PL.

Continue below after submitting the prelab.

 Follow up on the Prelab

After L124PL comes due, open the assignment to review your responses, the key, and the grader's comments. You'll need to make corrections as part of your final report. Open WebAssign L124 and make the corrections in the first item.

 Form of Your Report

You'll submit your report as a Logger Pro file in WebAssign L124. Present your work in a way consistent with course expectations. See the guide, Drawing and Analyzing Graphs as needed to review protocols. Show your work to make your process of analysis clear.

 Experimental Design and Method

View the second item in WebAssign L124. This will give your randomized Seed number. Enter that number into the animation and click Reset before collecting data. Note that the coefficient of static friction is displayed in the Outputs pane of the animation. This will be the expected (accepted) value.

The method of collecting data is to enter a particular radius in the animation, run it, and find the point at which the coin starts to slide. Use the step frame buttons to get as close to the instant of sliding as possible. The frequency is displayed in the Outputs pane. You may notice that if you run the animation repeatedly for the same conditions, the frequency at sliding shows some variation. This is the built-in uncertainty that was mentioned earlier.

Collect data from the animation for 5 different values of the independent variable. The maximum that the radius can be is, of course, the radius of the turntable, 0.200 m. (Assume 3 significant figures even though IWP drops final zeros.) Use 0.020 m as a minimum radius. Below that, the animation may stop before the coin slides. Select your 5 values to span the range of minimum to maximum radius.

 Graphical Analysis

Since one of the goals of the lab is for you to demonstrate the skills of graphical analysis that you've learned this semester, a step-by-step procedure isn't provided here. Review the goals of the experiment and the required method of analysis. Then carry out the analysis.

 Error Analysis

Since the data is simulated, an error analysis isn't required. Do, however, calculate your experimental error, as this will give you a measure of the accuracy of your data collection and analysis.

 Revisiting Part D of the Prelab

Open the prelab assignment on WebAssign again, and review Part D. Revise or reconstruct your response to the question. Use fundamental physics in your explanation. This should include i) describing how the acceleration required to maintain an object in circular motion depends on the radius of the path and how you know the acceleration has that dependence and ii) whether there is sufficient static friction force to provide that acceleration and how you know.

 Submission

Upload your Logger Pro file to WA L124.


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