Graphing Review

Variables On graphs, we can see whether the dependent variable increases or decreases with the independent variable. Dependent variable: results that were measured/calculated Independent variables: the thing you chose to change for each test

1. The Data Graphs are made from data tables…. The first column should be your independent variable Time (sec) Distance (m) 5 10.2 10 20.8 The second column is your dependent

2. Labelling the Graph Always label your axes with units! Distance (m) vs. Time (s) Always label your axes with units! Distance (m) Titles are usually Y vs. X Time (s)

3. Making a Scale Example: Scale = range (the highest number you need to plot) lines (how many lines are on your graph paper) Example: If you need to plot the numbers 0, 2, 5, 8, 15, 25, and 30 and your graph had 15 lines on it. Scale = range = 30 = 2 per line! (count by 2 per line) lines 15

4. Plotting! – Plot the data After the information is plotted, determine whether the points should straight line relationship or a curved line relationship Drawing a best fit line: use a ruler – you may not go through EVERY point (that’s OK – it’s best fit)

Interpolation: read data off a graph from the area between the known points on a graph Extrapolation: read data off a graph beyond the last plotted point (extend the line)

5. Slope! To calculate the slope of the line of a graph, you need to pick 2 points on the graph (preferably not plotted points).

Distance – Time Graphs Time is usually the independent variable (plotted on the x-axis) Distance is usually the dependent variable (plotted on the y-axis)

Distance – Time Graphs For a Distance-Time graph the slope is distance/time which is equal to SPEED! Average speed is calculated from the slope of the line

The line on this graph is straight and pointing upward to the right The line on this graph is straight and pointing upward to the right. This indicates that there is a direct relationship between distance and time!

How can the slope of a the best-fit line represent both ∆d = v ∆t and y = mx + b?? Let’s Review: y = mx + b y – dependent variable (y axis) X – independent variable (x axis) m – the slope of the line b – the y intercept of the line ∆d = v ∆t – equation relating distance, speed and time y = mx + b – the general equation for a straight line