Lab 4 - Tagged

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Pennsylvania State University *

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Course

211

Subject

Chemistry

Date

Feb 20, 2024

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pdf

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4

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A MODEL FOR KINETIC FRICTION – PART 2 INTRODUCTORY INSTRUCTIONS This lab will be graded using scientific ability rubrics. To help you know what we expect, the rubrics have been included along with the instructions for each question. Lab goals: In this lab, you will design an experiment to determine the relationship between kinetic friction and mass of the object. You will also determine the coefficient of kinetic friction of the IOLab on a surface of your choice. Equipment available: You will need the IOLab with computer/software and a horizontal surface (always use the same one!). You may need the “hook” attachment and a small piece of string to pull the IOLab. You will also need coins, pens or other small objects and tape in order to change the mass of the IOLab. Documents and videos needed. We have multiple pages to read in the course content about this lab. These pages include videos instructions on how to use StatKey for two quantitative variables. In this lab, we will encounter for the first time the notion of the “best fit” line. Phenomenon to Observe: When two objects in contact move relative to one another, the atoms at the interface interact electrically to create a force that resists the motion. This force is called kinetic friction and we know that it is always in the direction opposite to motion parallel to the interface. Predicting the value of the friction force from the starting principles of material science and electromagnetism is still an open problem in physics. It is a very hard and complex phenomenon in surface dynamics. It turns out that the most important variable that determines the friction is the normal force which usually depends on the mass of the object on top. The properties of the surface can be all encoded into a coefficient of kinetic friction which must be determined case by case. In this lab, you will need to find ways to measure correctly the value of the kinetic of friction and the value of the mass of the IOLab. By changing the mass of the IOLAB but keeping the surface the same, we can determine the relation between kinetic friction and mass. Variables : Independent variable: mass of the IOLab + coins…
A Model for Kinetic Friction - Part 2 Page 2 of 4 Dependent variable 1: measured kinetic friction Dependent variable 2: measured kinetic friction by an alternative method? Controlled variables. Surface on which IOLab slide, temperature of the room or surfaces, etc.. Both dependent and independent variables are quantitative variable (they could be any numbers).
A Model for Kinetic Friction - Part 2 Page 3 of 4 MASS DEPENDENCE OF KINETIC FRICTION 1. How does the kinetic friction depend on mass? Describe how you will attempt to answer this question. You will want to measure the kinetic friction while varying the mass of the IOLab. But how will you do that in practice? Will you choose Method A or Method B of the previous Lab to measure the kinetic friction? How will you vary the mass of the IOLab? How many times will you measure the kinetic friction for each different mass? Make sure that you are clear on how to proceed. For changing the mass of the IOLab, we recommend to tape additional objects (coins, pens, …) to the IOLab in a way that does not hinder the measurement of the kinetic friction. You also want to attach objects heavy enough for better results, but do not go too much over a total mass of 0.4kg, IOLab included. Inadequate Adequate Good Is able to describe how to use available equipment to make measurements All chosen measurements can be made, but no details are given about how it is done. All chosen measurements can be made, but the details of how it is done are vague or incomplete. All chosen measurements can be made and all details of how it is done are clearly provided. 2. Perform your designed experiment and record all your data in Excel. Save as a .cvs file. This is an experiment with two quantitative variables. We will use the “two quantitative variables” option in StatKey. The data will be represented as a dot plot where each data point appears as a dot in a x-y plane. We will use the correlation statistic to determine how strongly two quantities are correlated. We will also use the slope and intercept of the regression line to quantify the correlation assuming that it is linear (a straight line). See video and notes in the course content webpage. Go to StatKey, go to “two quantitative variables” and upload your data using the “upload file” button. Click on “show your regression line”. Take a screenshot and upload your graph here (with the statistics on the left included).
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A Model for Kinetic Friction - Part 2 Page 4 of 4 Graded on correctness. 3. StatKey gives you the slope and intercept of the regression line fitting your data. What is the slope? Analyze your data and make sense of it. Write down any notes here. Estimate the size of the errors if you can. Make sure you explain how you are accounting for outliers if they are any. Inadequate Adequate Good Is able to identify a pattern in the data The pattern described is irrelevant or inconsistent with the data The pattern has minor errors or omissions. The patterns represent the relevant trend in the data. When possible, the trend is described in words. 4. Use the fit to determine physical data. So now let us assume a model of friction where f k = μ k n . Can you determine the coefficient of kinetic friction µ k from the data? What does the intercept mean (if anything)? See course content on “fitting data”. Graded on correctness. 5. Based on your data, identify shortcomings of the experiment and what action you should take next to improve your conclusions. Inadequate Adequate Good Is able to identify the shortcomings in an experiment and suggest improvements. The shortcomings are described vaguely and no suggestions for improvements are made. Not all aspects of the design are considered in terms of shortcomings or improvements. All major shortcomings of the experiment are identified and reasonable suggestions for improvement are made.