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International School of Amsterdam IB Diploma Physics Investigating the Investigation Now that you have some experience with practical investigations, it is time to review the requirements, in order to ensure that you are working towards fulfilling all the criteria as well as possible. We will work through a typical investigation!

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A Typical Investigation Scenario Any teacher knows that the smallest things can be a distraction to students and the most innocent objects can be misused. An example is the simple rubber band. Rather than being used to bind bundles of loose objects together, their elastic properties are liable to be used to turn them into projectiles. Task Your task is to investigate a factor of your own choosing that affects the flight of a rubber band.

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Design - The Aim n The aim must be a focussed problem or research question n It cannot be simply a restatement of the general task that has been provided n The task may, however, specify the dependent variable n In this case it does not!

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The Dependent Variable n “The flight of a rubber band” is a very general description n There are several characteristics of “flight” that are readily measurable and could become our dependent variable n e.g. Range, flight time, or maximum height

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The Independent Variable n Consider what variables you could investigate. In this case, some possibilities are: Amount of Stretch Angle of Launch The rubber band, e.g. length, thickness n Choose one to investigate, bearing in mind that once you finally reach a conclusion, you will have to try and explain it using basic principles.

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The Controlled Variables n All the possible independent variables will be among the controlled variables for the investigation n Other factors that might influence the results must also be controlled Possibility of Wind Launch height Are bounces allowed?

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The Apparatus and Materials n List all the apparatus and materials you will use in your investigation n You may need to revise this list when you have completed your plan for the method n Be specific, especially with the ranges of meters

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The Method n Give enough detail so that someone else could follow it and end up doing exactly the same as you would n Scientific texts use an impersonal, passive style. (“The rubber band will be stretched back to the 10 cm mark on the ruler…”) n Write in the future tense. Anything else is a give-away that you have written a report afterwards, not a plan beforehand.

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Controlling the Variables n Describe how to set up the apparatus, and adjustments you need to make n You may include a diagram n Explain how it is used in the experiment n Make sure you refer to the independent, controlled and dependent variables in this stage

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Collecting Sufficient Data n Indicate any measurements that will be made once at the start and recorded individually n For the independent variable, give the starting value, size of step, the final value and how many repeats. (e.g. beginning with an angle of 0 degrees from horizontal and increasing in steps of 10 degrees up to a maximum of 80 degrees, firing 5 times at each angle.) n Give details of how to make the measurements, especially the dependent variable.

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Data Collection n First record any one-off data n Draw up a result table for most of the results Headings with units and uncertainties at the top Independent variable in the first column Dependent variable second You may include columns for processed data

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Uncertainties n Remember that all measured quantities have a degree of uncertainty n You need to allow for the uncertainty that arises in making the measurement and the uncertainty inherent in the quantity itself –In this case, you may be able to measure the range of a flight to the nearest 0.01 m –However, repeated flights may land up to 0.1 m apart n Give 1 s.f. in the uncertainty and the same d.p. in the measurement.

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Data Processing n Data may be processed mathematically, graphically or both n Errors and uncertainties must be taken into account for the assessment of aspect 3 of DCP n Clear presentation is required, making your working easy to follow n With graphs, show where and how the gradient has been calculated

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Calculations n Show individual calculations in full n Show sample calculations if you have used a spreadsheet or made repeated calculations n Show details of your error analysis (an example will do if there are repeated similar calculations)

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Drawing Graphs n Generally line graphs are required Dependent variable on the vertical axis Independent variable on the horizontal axis Draw line of best fit or a smooth curve Show error bars, or note if they are too small to show Include max. and min. error lines n The requirements are the same for computer-assisted graphing

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Conclusion n State any numerical conclusion clearly, with uncertainty n Compare your answer with an expected value or literature value. (Does that value lie within the range of your uncertainty? - It should!) n Describe any relationship using the terms “direct”, “inverse”, or “proportional” and explain how the graph shows this. n You must also try and justify your conclusion (using basic principles or explaining the logic of your deduction)

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Evaluating the Method n Refer to any difficulties that arose n Note which measurements contributed most to the uncertainty in your answer n Focus on these when suggesting improvements to the method n You are being asked for evaluation not reflection. So, keep it impersonal. Do not refer to learning from the experience or working well with your partner.

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