Graphing is an effective way of showing the

Graphing is an effective way of showing the relationship between variables. Page 24 Science 10/Kennedy/2016 1

1. 5 Graphing Page 24 Graphing experimental data is an effective way of showing relationships between variables. Science 10/Kennedy/2016 2

Graphing techniques Page 24 Graphs are used to communicate relationships – how one thing affects another. Step Step 1: 2: 3: 4: 5: 6: Select the Axes Select a Scale Plot the Data Draw the Best-fit Line Title (responding versus manipulated) Calculate slope Your graph should be neat and not cluttered. Science 10/Kennedy/2016 3

Graphing techniques Page 24 Graphs are used to communicate relationships – how one thing affects another. Step 1: Select the Axes Responding y Manipulated x Time is always on the x-axis Science 10/Kennedy/2016 4

Step 2: Select a Scale Page 24 Bad Good 3. 0 2. 0 1. 0 The graph should take up at least 2/3 of the graph paper. Science 10/Kennedy/2016 5

Page 24 Select whichever orientation works best for your graph. Portrait view Landscape view Science 10/Kennedy/2016 6

Page 24 Don’t crowd the axis. 6. 0 8. 0 1. 0 3. 0 2. 0 4. 0 5. 0 7. 0 9. 0 10. 0 15. 0 20. 0 25. 0 Poor Good Science 10/Kennedy/2016 7

When drawing a graph have a: • clear, plastic ruler/straight edge. You need to be able to see through the ruler to graph properly. • sharp pencil. Thin lines are more precise and produce better results. Whenever you have to draw a straight line, use a ruler/straight edge. Science 10/Kennedy/2016 8

Step 3: Plot the Data Page 24 1. Place a dot at the data point 2. Circle the data point Science 10/Kennedy/2016 9

Step 4: Draw the Best-fit Line Page 24 A good best fit line should: • Have as many dots as possible on the line. • Have as many dots above the line as below • All the dots as close as possible to the line Science 10/Kennedy/2016 10

Step 4: Draw the Best-fit Line Page 24 Best-fit lines and data points A best fit line should be as close as possible to all the points. This will result in as many points above the line as are before the line. A best fit line results in a type of average Do not connect the dots! A good best fit line should: • Have as many dots as possible on the line. • Have as many dots above the line as below • All the dots as close as possible to the line Science 10/Kennedy/2016 11

Page 24 Best fit lines Connect the dots – bad! Best fit line – good Use a clear plastic straight edge for best results Science 10/Kennedy/2016 12

Page 24 When drawing the best fit line, lift your pencil so as not to draw over the data point Science 10/Kennedy/2016 13

Lines Connect the dots – bad! Force through zero – bad! Connect first to last – bad! Best fit line – good! Science 10/Kennedy/2016 14

Page 24 Extrapolate and interpolate Extrapolate is extending the line beyond available data Interpolate is drawing a line between available data Science 10/Kennedy/2016 15

Page 34 Stray data points If a data point does not line up well with the rest of the dots then you may reject it as bad data. Draw an x through it or a place a question mark beside it. 40. 0 Mass (g) 30. 0 20. 0 10 20 30 40 50 Volume (m. L) Science 10/Kennedy/2016 16

Step 5: Title (responding versus manipulated) Example: Distance versus time Distance as a function of time Page 25 Mass of water as a function of Volume 40. 0 Mass (g) 30. 0 20. 0 10 20 30 40 50 Volume (m. L) Science 10/Kennedy/2016 17

Step 6: Calculate Slope • • Page 25 Slope is a measure of steepness of a line The symbol “m” is often used for slope Slope is the same anywhere on the straight line. Science 10/Kennedy/2016 18

Identify the line having the greater slope. A Steeper, therefore greater slope B Science 10/Kennedy/2016 19

Negative slope y y Positive slope x x Undefined slope y y Zero slope x x Science 10/Kennedy/2016 20

When calculating slope: Page 25 • Don’t use data points as slope points • Select two points that are relatively far apart • Use your clear plastic ruler 40. 0 to carefully mark the two slope points Mass of water as a function of Volume 38, 37. 5 Mass (g) 30. 0 20. 0 12. 0, 11. 6 10. 0 10 20 30 40 50 Volume (m. L) Science 10/Kennedy/2016 21

Page 25 Calculating Slope • Don’t use data points as slope points • Select two points that are relatively far apart • Use your clear plastic ruler to carefully mark the two slope points • As best as possible, use points that are easy to estimate; places where the graph line crosses grid lines. Science 10/Kennedy/2016 22

Selecting and marking slope points: Page 25 • You may select points that are as easy to read (estimate) as possible but make sure your estimate is actually on the graph. • Don’t use the nearest intersection to your best fit line • Take more care and mark slope points on the line. Science 10/Kennedy/2016 23

Page 25 Calculating Slope = rise run y 2 – y 1 x 2 – x 1 Show all work: 1. formula 2. substitution with units 3. answer Science 10/Kennedy/2016 24

Page 27 If your graph curves you can use a flexible ruler or free-hand the line Distance as a function of Time 4. 0 distance (m) 3. 0 2. 0 1. 0 2. 0 3. 0 time (s) Science 10/Kennedy/2016 4. 0 5. 0 p. 24 #1 - 6 Do 25