Practical Investigation: Advice and Hints

1. Advice and Hints on doing the Practical Investigation Dan O’Keeffe Vicphysics Teachers’ Network www.vicphysics.org

2. What I will cover • Your task • What do you get out of the PI? • Deciding on a topic • Identifying variables • Formulating a plan • Hints for the students • Using the log book • Taking measurements • Analysing data • Assembling a poster

3. Your task: To design and conduct a practical investigation into a topic of your choice. You can choose the equipment and measuring instruments you want, and decide the path your curiosity takes you. It is a break from other topics. No test at the end! It assesses your skills of planning and organisation. It will take about 3 – 4 weeks of class time.

4. What do you get out of it? Benefits: Sense of ownership of the task, Opportunity to work independently on a topic that interests you, Your success does not depend on how well you do in a test, but rather on you being: focussed, organised, careful, thoughtful, analytical and thorough.

5. What do you get out of it? But, there may be worries: Being unsure about being on the right track, Being stuck when the results don’t make sense. Problems aren’t a negative, they are an opportunity for you to reveal your capabilities to: analyse the possible causes, and suggest solutions. Your teacher is there as a resource and a mentor. If we knew what we were doing, it would not be called research: Albert Einstein

6. Deciding what to investigate • Hobby, sport • An area of physics of interest to you • Brainstorming • Vicphysics website for lists of topics • Your teacher may also have their own prompt list • Come up with 3 ideas

7. Helping you decide what to investigate Brainstorming

8. What makes a good topic? Can be done with basic equipment, Generates a lot of data quite quickly, Reveals hidden depths, Engages you. Simplify a complex topic down to something easily measurable.

9. Your teacher’s approval Your teacher might consider: • Does the school have the equipment that might be needed? • Can the topic be properly investigated in 3 – 4 weeks? • Does it provide enough challenge? • Can equipment be set up and initial measurements taken in the first period of the experimental phase?

10. Your teacher’s approval Your teacher might also consider: Safety and supervision issues? Is the group size appropriate? (Most topics can be done by one student, some need two)

11. Identifying Variables Independent variables: Aspects you can change. Dependent variables Aspects that change because you changed something else. Controlled variables Independent variables that you decide to vary, they are held constant.

12. Identifying Variables Types of variables: • Continuous can be represented by a real number and plotted on an x-y graph, e.g. drop height. • Discrete can be represented by an integer and can be plotted on an x-y graph, e.g. strings on a parachute. • Categorical are qualitatively different, can be graphed on bar chart, e.g. types of surfaces a ball is bounced on.

13. Variables: Requirements Year 11: Two independent variables, one of which should be continuous. Year 12: Two continuous independent variables

14. Detailed Research Plan It should include: • Detailed statement of purpose, • Two specific research questions, identifying independent and dependent variables, • Equipment required, • Experimental design (including diagram) • Physics relationships to be used in calculations. With a sample calculation with typical data of physical quantities relevant to your topic. • Your teacher is likely to ask you to complete this in class and may do it under test conditions, assess it and then give you feedback.

15. Measuring Instruments As well as the usual scales, rulers, stop watches and meters, but also: • micrometers, vernier callipers, • top loading balances, • data loggers and • software such as Tracker. Note: Technology will enable you measure quantities you would not otherwise be able to do, but it does not necessarily make for a better topic.

16. Using the Log Book It is compulsory that you maintain a log book, It may be hard copy or electronic, … but your teacher will want to view it regularly.

17. Using the Log Book What to put in it? The plan, including photos of set up All your data, Any difficulties and solutions, Graphs, their analysis and interpretation, Uncertainty calculations, Comments, ideas and possibilities, Discussion of results, Draft comments on conclusion. It will be a significant component of your assessment. It will be the supporting document to your poster.

18. Using the Log Book Format? A separate bound exercise book If electronic, best on school website Not loose sheets of paper! For Excel data and graphs, paste a print in log book How to use it: Leave plenty of space for later annotations Pages dated At the end of each day write down what you plan to do the next day.

19. Advice and Hints This is real research, so ... • There will be teething problems, so record difficulties and solutions in the log book, • Do some quick readings to clarify if: • equipment is OK, and • technique is OK, • Seeking help from the teacher, is not a sign of failure, it is a sensible response to problems, • Do repeated trials across a large range of values.

20. Advice and Hints Analyse data progressively, look for patterns and gaps, Don’t ‘stockpile data’, Record uncertainties of instruments and measurements as you go, Take photos of experimental set up for poster.

21. Uncertainty in a Measurement Limit of reading an instrument Instrument with a scale: least count (smallest subdivision on scale) = 1 mm resolution (smallest change we can detect) ≈ 1/2 divSo uncertainty here is 1/2 of least count ≈ 0.5 mmSo length = (43 ± 0.5) mm This means the actual length is between 42.5 and 43.5 mm.

22. 0.30 ± 0.01 A 2.1 ± 0.05 V

23. Uncertainty in a Measurement Limit of reading an instrument: Digital readout The uncertainty is half the last precise digit. Precision of last digit is 0.1oC Uncertainty is 0.05 oC, so Measurement is 27.6 ± 0.05 oC The actual temp is somewhere Between 27.55 oC and 27.65 oC

24. Conventions when using Uncertainty Put units at the end e.g. 25 ± 1 s, not 25 s ± 1 s With large or small numbers using standard form, the power of ten and unit are both placed at the end, e.g. (6.3 ± 0.2)  10-8 m, not 6.3  10-8 ± 0.2  10-8 m Uncertainties normally stated to one sig fig. A measurement should be quoted to the same decimal place as its absolute uncertainty, e.g. 2.60 ± 0.02 s, not 2.604 ± 0.02 s or 2.6 ± 0.02 s

25. Uncertainty in Repeated Trials Set of temperature readings: 19.4, 19.6, 19.5, 19.8, 19.2, 19.1, 19.5 and 19.2 oC Average = 19.4 oC Range: = 19.1 to 19.8 oC Uncertainty = Larger difference = 0.4 oC So plotted data = 19.4 ± 0.4oC

26. Uncertainty and graphs • Uncertainty is represented on a graph by an ‘Error bar’ about each data point. • Size of the error bar = uncertainty.

27. Line Of Best Fit Draw smooth line through all the error bars. Avoid forcing line to go through a maximum number of data points. It gives different pairs of readings different rather than identical weightings. As many data points above the line as below the line. Max and min values for gradient of line of best fit, also for intercept.

28. m/s2 m/s2 m/s2 0.9 ± 0.1 m/s2 0.8 ± 0.2 m/s

29. Additional Analysis Skills Such as: • Calculating percentage uncertainty • Calculating uncertainties when: + adding or subtracting measurements, and * multiplying or dividing measurements.

30. Combining Measurements: Uncertainty Adding or subtracting quantities Rule: You add uncertainties e.g. Change in velocity of a bouncing ball on impact Initial velocity = 6.26 ± 0.03 m s-1 Final velocity = 4.85 ± 0.06 m s-1 Change in velocity = 4.85 - (- 6.26) m s-1 = 11.11 m s-1 Uncertainty = 0.03 + 0.06 = 0.09 So, change in velocity is 11.11 ± 0.09 m s-1

31. Combining Measurements: Uncertainty Multiplying or dividing quantities Problem: Drop height = 2.00 ± 0.01 m Rebound height = 1.20 ± 0.03 m What percentage of the initial gravitational potential energy is retained? Answer: = (mghreboundheight ) / ( mghdrop height) x 100 = (rebound height / drop height) x 100 = 60.0 % How do we determine the uncertainty in this value? Calculate a Percentage Uncertainty for each, and Add these.

32. Percentage Uncertainty X Percentage Uncertainty (PU) = Uncertainty 100 Measurement 1 Drop Height (PU) = (0.01/2.00) x (100/1) = 0.5% Rebound Height (PU)= (0.03/1.20) x (100/1) = 2.5% Energy Efficiency (PU) = 0.5% + 2.5% = 3.0% Uncertainty = (3.0 / 100) x 60.0 = 1.8, So answer is 60.0 ± 1.8, But rounding gives 60 ± 2.

33. Using Excel • An efficient way of storing measurements. • Great for drawing graphs and finding the equations of lines of best fit. • Useful Excel Functions such as: Average, Max, Min, etc • Creating formulas for KE, GPE, etc • Back up data daily.

34. Using Excel Graphs (or Charts): • Two continuous variables: Use Type: XY Scatter and Sub type: dot points without lines joining the dots • Categorical independent variable: Use Type: Column Equation of line of best fit • Right click on a data point and select ‘Add trendline’. Check ‘Options’ to display equation. • Choose either ‘linear’ or ‘power’. Avoid ‘exponential’. • Don’t assume line passes through the origin, unless (0,0) is a real data point.

35. Using Excel Limitations: The values of the constants in the equation are likely to contain more digits than is justified by the uncertainties in your data, e.g. ‘y = -1.679x - 4.5908’. Excel can insert error bars, but they can be tricky. You need to know what you are doing so that the error bars properly reflect your data, rather than being just added for visual effect.

36. Assembling a Poster Compulsory for Year 12 Optional for Year 11 Possible formats of poster: • A PowerPoint slide using a template, • A one page pdf file, • Hard copy or digital copy on a single poster. Powerpoint templates are available.

37. Title of Physics Practical Investigation Student’s Name Introduction Discussion Results Explanation for undertaking the investigation, including a clear aim. (One sentence should be enough.) Relevant background physics concepts. (Just definitions and equations should suffice.) Presentation of collected data/evidence in appropriate format to illustrate trends, patterns and/or relationships. • Analysis and evaluation of primary data • Identification of outliers and their subsequent treatment • Identification of limitations in: • Selection of data showing number of repeated measurements and range of values, • Sample calculation, • Sample determination of uncertainty and error bars, • Graphs with descriptions, at least 2, but less than 5, • Analysis of graphs including lines of best fit, gradients and intercepts, • Effect of uncertainties. • Data, both in the range of values and number of repeated measurements, and • Experimental method, and so • Suggested improvements and • Further aspects you would like to investigate, Methodology Summary that outlines the methodology used in the investigation and is authenticated by logbook entries. • Description of independent and dependent variables, including which are continuous, • Equipment and measuring instruments, • Sketch of equipment layout as well as a photo, • Identification and management of relevant risks … • Linking of results to relevant physics concepts. Conclusion References and acknowledgements Provide a precise and detailed response to your question. Need only be a short paragraph. Rarely needed in student physics investigations.

38. Assembling a Poster Your poster should give an overview of your investigation. Your logbook will provide the details. Your task: Paste your content into the various boxes. Include a photo of your set up. Adjust the sizes of boxes to fill the space of the poster, without making it look cluttered. Edit your content, so that your story line is coherent and balanced. This should not be a laborious task, .. really only about an hour or two.

40. Experimentation is the least arrogant method of gaining knowledge. The experimenter humbly asks a question of nature. Isaac Asimov The farther the experiment is from theory, the closer it is to the Nobel Prize. Irene Joliot-Curie You can only analyse the data you have. Be strategic about what to gather ... Marie Curie I never allow myself to become discouraged under any circumstances. After we had conducted thousands of experiments on a certain project without solving the problem, … we had learned something. For we had learned for a certainty that the thing couldn’t be done that way, and that we would have to try some other way. We sometimes learn a lot from our failures if we have put into the effort the best thought and work we are capable of. Thomas Edison It never occurred to me that there was going to be any stumbling block. Not that I had the answer, but [I had] the joy of going at it. When you have that joy, you do the right experiments. You let the material tell you where to go … Barbara McClintock If we knew what we were doing, it would not be called research, Albert Einstein