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# LAB1 - Graphing Experimental Data Objective In this...

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Graphing Experimental Data Objective: In this exercise you will review how to collect and graph experimental data. Background: A graph represents the relationship between a pair of variables. Normally, a well-planned experiment results in the measurement of one physical or chemical property and its dependence on another. The property which is changed in a controlled manner is called the "independent variable", while the variable which responds to this change is called the "dependent variable". As a matter of form, the independent variable is plotted on the horizontal, or x-axis, while the dependent variable is plotted on the vertical, or y- axis. The x-axis is referred to in mathematics as the abscissa , while the y-axis is referred to as the ordinate . The graph should expand to fill as much of the graph paper as possible so that the experimental data can be plotted with the greatest precision. Once the data points have been plotted, the line best represented by the points is drawn. Due to experimental uncertainty and error, the data points will not lie exactly on this line. The drawing of a line is equivalent to taking a weighted average of the data points. The best line should be drawn with a transparent straight edge or ruler so that all of the points can be seen at the same time (see Figure 1). y = m x + b Δ x Δ Δ y Slope = m = Δ y Δ x Title Abscissa (independent variable) O r d i n a t e ( p v l ) Figure 1

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Once the graph has been made, it is often useful to determine an equation in order to represent the information in the most concise way possible. The discussion herein deals only with straight-line relationships. In addition to expressing the relationship between variables, the slope and y-intercept of a straight line can often be related to physical values. The general form for the equation of a straight line relating the variables x and y is
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LAB1 - Graphing Experimental Data Objective In this...

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