Physics 1011 2111 Mechanics

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Table of Contents,Physics 1011 2111 Labs General Guidelines 3. Introduction to Statistics Error and Measurement 5. 1 The Determination of Gravitational Acceleration 11. 2 Projectile Motion 16,3 Newton s Second Law The Atwood Machine 20. 4 Friction 27,5 The Work Energy Theorem 32,6 Conservation of Linear Momentum 36. 7 Rotational and Translational Energies 43,8 Periodic Motion and Resonance 51. Appendix A Excel the Basics 57,Appendix B DataStudio Instructions 63.
Physics 1011 2111 Labs General Guidelines, The Physics 1011 and 2111 labs will be divided into small groups so you will either be working. with one lab partner or for the larger classes in a small group You and your lab partner s will. work together but you each must submit an individual lab report with a discussion of the lab. and interpretation of results in your own words, The laboratory classroom is located in the west wing of Benton Hall Room 331. Laboratory attendance is mandatory and roll will be taken At the beginning of each lab you will. sign out a lab kit and your lab instructor will check it in when you finish the lab If you miss a. lab session it is your responsibility to contact the lab instructor to pick up any missed handouts. or information for the following week s session The lab instructor may allow you to make up a. missed experiment if you miss the lab for a valid medical reason If makeup labs are. permitted labs must be made up within a week of the original lab date See your individual. professor s syllabus for details about their rules for makeup labs. Always read the experiment before coming to the lab This is really important and will. help you get the most out of the lab Bring your calculator to lab and take good notes. when the lab instructor gives detailed information about the experiment and about what. s he expects in the lab report, Lab reports MUST be typed If you have trouble finding computer facilities and don t. have a computer at home see the lab instructors or the course instructor and we will help. you find a computer to work on, Lab reports should include your name the name of your lab partner the lab section e g. Tuesday 12 30 the date the experiment was performed and the title of the experiment. This is a recommended guideline The lab instructor has the final say in which details to. include and how to format your lab report, You may find it useful to visit the Lab Connection website which you can access via the.
Physics Department website http www umsl edu physics. The lab report itself should contain the following sections. Purpose State in your own words the purpose of the experiment. Procedure Describe the procedure in your own words Describe also any novel approaches you. took difficulties you had or interesting observations These descriptions need to be in. scientific style as professionally written as if you were going to submit the lab report to a. scientific journal Writing things like This experiment was fun is NOT what we are looking. Data graphs List all data taken in the experiment in tabular form whenever possible. Make sure that you give the units for all physical quantities All graphs and tables should be. neatly arranged and clearly labeled with titles, Calculations Show clearly all the calculations you performed on the data Show all. equations you used, If calculations are used to obtain data that is plotted in the graphs you may want to show the. calculations before the graphs For example you might make some measurements and plot the. raw data Then you might do some calculations on the raw data and plot the results In that case. your results section should show 1 table of original data 2 graph of original data 3. calculations equations and table of calculated results and 4 graphs of calculated results. Alternately you might show calculated quantities in columns next to the original measurements. For each experiment we will give a sample data table that you can copy and paste into your lab. report as a guide to how to present the data The main point is to have the data and. calculations presented clearly You want the lab instructor to be able to clearly follow your. thought process to be able to see exactly what you measured and what you calculated. Answer all the questions posed in the lab manual,Conclusions. What did you conclude from the experiment What quantities were measured Were the results. of the measurements what you expected Describe possible sources and types of error in your. measurements Tie your results back to the original purpose of the experiment. The lab reports are due at the beginning of the following session unless stated otherwise by your. lab instructor, Graded reports will typically be handed back a week after they are turned in End of semester. graded lab reports will be handed back at your lecture or can be picked up from your professor. after the end of the semester, All measurements taken in the lab should be in SI Syst me Internationale units formerly.
known as MKS units meters kilograms and seconds unless explicitly stated otherwise by. your lab instructor, Happy experimenting And when you get frustrated remember that Galileo did all this under. house arrest,Introduction to Statistics Error and,Measurement. Throughout the semester we will be making measurements When you do an experiment it is. important to be able to evaluate how well you can trust your measurements For example the. known value of g the acceleration due to gravity is 9 81 m s2 means approximately. equal to If you make a measurement that says g 10 1 m s2 is that measurement wrong. How do you compare that measurement to the known value of g Suppose you measure some. quantity that is not known You may make a number of measurements and get several different. results For example suppose you measure the mass of an object three times and get three. different values 5 kg 4 8 kg and 5 4 kg Can you evaluate what the real mass of the object is. from those measurements, The mathematical tools we will learn in this lab will answer some of these questions They are. some of the most basic methods of statistical analysis they will allow us to give information. about our measurements in a standard concise way and to evaluate how correct our. measurements are The methods we will cover are used in all areas of science which involve. taking any measurements from popularity polls of politicians to evaluating the results of a. clinical trial to making precise measurements of basic physical quantities. Let s start with the basics of the different kinds of errors and how to measure them. Types of Errors, There are two types of errors encountered in experimental physics systematic errors and. random errors,Systematic errors can be introduced,by the design of the experiment.
by problems with the instruments you are using to take your data. by your own biases, Consider a very simple experiment designed to measure the dimensions of a particular piece of. material precisely A systematic error of could be introduced if the measuring instrument is. calibrated improperly For example a scale might be set a little too low so that what reads as. zero is really 1 kg Everything you measure on the scale will come out one kilogram lighter. than it really is If a particular observer always tends to overestimate the size of a measurement. that would also be a systematic error but one related to the personal characteristics of the. experimenter, Random errors are produced by unpredictable and uncontrollable variations in the experiment. These can be due to the limits of the precision of the measuring device or due to the. experimenter s inability to make the same measurement in precisely the same way each time. Even if systematic errors can be eliminated by good experimental design there will always be. some uncertainty due to random errors Numerical values measured in experiments are therefore. never absolutely precise there is always some uncertainty. Accuracy and Precision, The accuracy of a measurement describes how close the experimental result comes to the actual. value That is it is a measure of the correctness of the result For example if two independent. experiments give the values 2 717 and 2 659 for e the base of the natural log the first value is. said to be more accurate because the actual value of e is 2 718. The precision of an experiment is a measure of the reproducibility of the result Suppose you. measure the same thing three times The precision would be a measure of how similar all the. measurements are to each other It is a measure of the magnitude of uncertainty in the result. Suppose one person weighs a cat and comes up with three different masses each time 10 kg 12. kg and 11 kg Suppose another person weighs the same cat and comes up with these three. masses 11 1 kg 11 5 kg and 11 3 kg The second person s measurement would be said to be. more precise Both people are likely to be scratched though. Significant Figures, When reading the value of an experimental measurement from a calibrated scale only a certain. number of figures or digits can be obtained or read That is only a certain number of figures are. significant The significant figures sometimes called significant digits of an experimentally. measured value include all the numbers that can be read directly from the instrument scale plus. one doubtful or estimated number For example if a ruler is graduated in millimeters mm you. can use that ruler to estimate a length up to one tenth of a millimeter For example suppose you. make a sequence of measurements of the length of some object using this ruler and get an. average value of 318 9811123 mm The measurement is only accurate to one decimal place so. you would report the number as 319 0 0 1 mm The zero is shown after the decimal point. because that digit is the last significant one All the other digits are meaningless and do not. convey any real information about your measurements Also when you are combining. measurements the most imprecise measurement is your limiting factor You can never have. more significant digits than your least accurate measurement. Data Analysis,Percent Error and Percent Difference.
How do you measure the size of an error The object of some experiments is to. measure the value of a well known quantity such as g You ll be making this measurement. yourselves in next week s experiment The most accurate value of these quantities measured by. teams of dedicated professional scientists is the value given in your textbooks and tables In. making a comparison between the results of your experiment and the accepted value measured. with much more precision in specialized laboratories you want to cite the percent error a. measurement of how much your measurement differs from the official value The absolute. difference between the experimental value E and the accepted value A is written E A where the. signs mean absolute value The fractional error is the ratio of this absolute difference over. the accepted value,Fractional error, Usually people convert this fractional error into a percent and give the percent error. Percent error x 100, Sometimes you need to compare two equally reliable results when an accepted value is. unknown This comparison is the percent difference which is the ratio of the absolute. difference between experimental results E1 and E2 to the average of the two values expressed. as a percent,Percent difference x 100,Mean Value, Even if systematic errors can be eliminated from an experiment the mean value of a set. of measurements of a quantity x is a better estimate of the true value of x than is any. single measurement For this reason experiments are often repeated a number of times If we. denote x as the mean value and there are N measurements x i where i varies from 1 to N. then x is defined by the following equation, In fact random errors are distributed according to a Gaussian distribution which looks like the. familiar bell curve In case you aren t familiar with it the symbol we just used is a capital. Greek letter sigma In math it is called a summation sign It means add up everything to the. right So in the equation above the sigma is a shorthand way of writing. x x1 x2 x3 xN,Mean Deviation, To obtain the mean deviation of a set of N measurements the absolute deviations of xi are.
determined that is,The mean deviation x is then, Example 1 1 What are the mean value and mean deviation of the set of numbers 5 42 6 18 5 70. 6 01 and 6 32,The mean is,N x 5 4 2 6 1 8 5 57 0 6 0 1 6 3 2 5 9 2 6 5 9 3. Note that since the original measurements were only valid to two decimal places the average. can only be valid to two decimal places as well so we round from 5 926 to 5 93. The absolute deviations for each measurement are,x1 5 42 5 93 0 51. x2 6 18 5 93 0 25,x3 5 70 5 93 0 23,x4 6 01 5 93 0 08. x5 6 32 5 93 0 39,Then the mean deviation is,N x 0 51 0 25 0 523 0 08 0 39 0 292 0 29.
Usually people report an experimental measurement as the mean plus or minus the mean. In our example the value would be reported like this 5 93 0 29. Standard Deviation, Statistical theory states that the precision of a measurement can be determined using a. quantity called the standard deviation called sigma this is the Greek lower case s The. standard deviation of a distribution of measurements is defined as follows. Physics 1011 2111 Labs General Guidelines The Physics 1011 and 2111 labs will be divided into small groups so you will either be working with one lab partner or for the larger classes in a small group

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