Name:Partner(s):Lab #1 The Scientific MethodDue 6/25ObjectiveThe lab is designed to remind you how to work with scientific data (including dealing withuncertainty) and to review experimental design.Uncertainty and ErrorSuppose you read a study in a magazine stating that in the general population 20-30% ofpeople have ear piercings and 1-3% of people have body piercings.Scientists would write this as25 +/- 5% of people have ear piercings.2 +/- 1% of people have body piercings.The first number is the result, and the second number is the random error in the result(sometimes also called the random uncertainty). Random error indicates how the resultsmight change if you did the survey many times. Usually, if you repeat the survey, yourresults will agree with the number quoted within the error.Generally, errors are quoted as percentages such that:percent error = 100 x (error / total).Through most of this course we will ask you to find your uncertainty. Often this is simpleenough. If you make a measurement your random uncertainty is the smallest value that youcan measure. If you are using a ruler you may be only able to tell things down to the nearestmm. In that case you would record your uncertainty as: +/- 1mm.Other times, you will be recording a number of data points. In this case, your randomuncertainty is the “scatter” of your data. For that your random uncertainty is how highabove and below an “average” value your data falls. For example you time how manyseconds it takes a rock to fall to the ground five times and measure: 5.0, 5.1, 4.9, 5.2, 4.8.You could report this as 5.0 +/- 0.2 seconds.In some cases, as in this assignment, your errors come from sampling a number of things,essentially an error in counting. The concept is that you are drawing your data points fromAstronomy 101 1 – 1 Introduction to Astronomya larger sample and somebody else doing the same experiment would draw a different datapoints and get a different answer – thus leading to uncertainty between the answers. Theequation for sampling error has been determined statistically to be:error =√numberTo summarize random error:• Measurement: smallest measurement one can determine• Data scatter: amount off of an “average”• Counting: square root of the number sampledThere is another type of error, systematic error. This would be the case if all of yourvalues were too big, or too small, instead of fluctuating up and down. Systematic error oftencomes from a bias in your methods, or equipment, say using a meter stick that isn’t reallya meter to measure things.In a few questions you will be asked to compare numbers. To compare two numbers scien-tifically, you must see if they agree within their respective uncertainties. It’s not enough tosay that two numbers are close together unless they are within their uncertainties of eachother. So the answer to this type of question involves a little math.To compare two numbers: If |A − B| < | (uncertainty in A + uncertainty in B) | then thetwo numbers are in agreement.Notice nowhere do the words human error show up. Please don’t ever use them. Instead oflisting your source of error as “human”, explain what specifically was the source.Astronomy 101 1 – 2 Introduction to AstronomyQuestionsThe following questions are based the hypothetical magazine survey on the percent of thegeneral population with ear and body piercings. You will be asked questions on designingan experiment to reproduce the results and interpreting the error. Use the following tableto record your results.Type of Piercing % Fromthe classsurvey% Errorfromtheclasssurvey% Fromthe UWsurvey% Errorfromthe UWsurvey% FromMaga-zine% ErrorFromMaga-zineEar Piercing 25% 5%Body Piercing 2% 1%1. (1 pt) Suppose you want to know the percentage of people in this class (teaching,auditing and enrolled) with ear/body piercings and to compare these results to theresults of the survey. State a reasonable hypothesis.2. (1 pt) How will you collect the necessary data?3. (5 pts) Using your desired method, find out how many people in the class have earand body piercings.Number Percent Error PercentErrorTotal Number of PeopleEar PiercingBody PiercingTransform the number of ear and body piercings into percents and fill in the appropriateresults column of the table directly above and table at the top of the page. Use thecorrect number of significant figures!Astronomy 101 1 – 3 Introduction to Astronomy4. (2 pts) What sort of errors could be associated with this data? Consider such thingssuch as whether anyone could have been lying, and whether everyone is present. Hint:This will probably not be a sampling error as you are probably not sampling a smallportion of the class in order to determine the data for the whole class.Transform your errors into percent errors and fill in the appropriate error column ofthe two tables on page 3. Use the correct number of significant figures!5. (1 pt) Now, suppose you were to extend your survey to find out if the numbers fromthe magazine survey on piercings are correct for the population of students at the UW.Write a new hypothesis that compares the the rate of piercings at the UW to that inthis classroom and to that of the general population (as determined from the magazinesurvey).6. (1 pt) Devise a method to collect a data set to test your hypothesis.7. (1 pt) How would you revise your plan if you only had two hours to collect the data?8. (1 pt) Devise an alternate plan in case the observations you want to make are impos-sible because you are locked in a high tower with no email or cell phone, just a windowto look out of.Astronomy 101 1 – 4 Introduction to Astronomy9. (1 pt) What is the problem with including only a small number of people in yoursample?10. (1 pt) What problems might occur if you only chose to look for subjects in a trendycafe?11. (2 pts) For questions 7-10 above, explicitly explain how similar types of issues couldapply in astronomical research12. (1 pt) How are the errors caused by the biases in questions 9 and 10 different? Whichhas a higher random error and which has a higher systematic error?Astronomy 101 1 – 5 Introduction to Astronomy13. (1 pt) Suppose you collect data on 523 students with the plan of extrapolating to theentire UW population. If the percentages from the magazine survey are correct (25%and 2%), what numbers of students with each type of piercing do you expect?14. (4 pts) Here are the hypothetical results from your new survey of 523
View Full Document
Unlocking...