Physical Science Lecture 4 Instructor: John H. Hamilton

Lecture overview Variables – Dependent – Independent Presenting and examining data Graphs – scatter – line – Bar – Pie chart How to look at Data

Variables Dependent variables – A dependent variable is a variable that changes in response to another variable. This is what is studied and expected to change when an independent variable is changed Independent variable – This is the variable that is controlled and changed to study what affect it has on the dependent variable. Sometimes called “controlled variable” or “manipulated variable”

examples You may measure the temperature of something cooling off over time. Temperature would be the dependent variable and time the independent variable You may measure the mass of a board for various lengths boards. Mass would be the dependent variable and length the independent variable

Presentation of data Charts or tables – Numbers are presented in a tabulated form – Typically independent variable is on the left column Graphs-ALWAYS graph your data and inspect visually – Scatter plots – Line graphs – Bar graphs – Pie graphs

Tables Two different tables showing distance travelled compared to time elapsed Distance travelled by Falling Objectdistance travelled by car on hwy time (s)distance (m)time (hr)Distance (km)

Good tables A good table contains the following traits – Proper significant digits – Left column is the independent variable – Each column is labeled and includes units – The table has a descriptive title

Graphs

Graphs need the following to be complete – Title – Axis labels – Units – Appropriate significant digits

Other graphs Bar graphs and pie charts – Bar graphs are good for showing the frequency something occurs – Pie charts are good at showing the relative occurrence between things. Pie charts are an area chart in which the total area represents 100%

Bar chart Scotland's population by blood group

Pie Chart

Making a Graph with a spreadsheet Microsoft excel Open office Other free spreadsheets

Creating a Graph in a Spreadsheet

Calculating Density Density is the amount of mass per unit volume. The standard SI density is kg/m 3

Lecture Review Variables – Dependent – independent Tables – title – Label rows or columns – Use correct significant digits Graphs – Types of Graphs Label Axis Title Use correct significant digits Always plot data!

Recommended Assignments Obtain a spreadsheet program if you don’t have one already Do one of the following – If you have access to a cooking thermometer, fully bake a potato that has been wrapped in aluminum foil. Ice the cooking thermometer to check the temperature near the center of the potato every 10 minutes for 80 minutes. Create a table and a chart showing temperature vs. time – If you have access to a thermometer that can measure room or outdoor temperatures then get a glass of ice water and use the thermometer to measure the temperature of the ice water every 10 minutes until the water is within 5 degrees C of the room temperature. When you take the temperatures, stir the water to make sure the temperature is the same through out, use just enough ice to get the water close to the freezing point. Create a table and a chart showing temperature vs. time In both cases, try to think about what the shape of the curves mean, in both cases consider any data points that look like they don’t fit and try to explain them