Welcome Physicists! Today: DQ: What is the difference between an independent and dependent variable? 1.Complete “Don’t Lose Your Marbles” 2.Data and Graph Types Study Guide 3.Graphing “Don’t Lose Your Marbles” Data 4.Energy Transformations HW: Data and Graph Types Practice ANNOUNCEMENT: Quiz This Friday (9/25) Types of Energy Energy Transformations

Variables and Constants Variable – Any factor that can change in a scientific investigation or experiment

Types of Variables Independent Variable What the scientist chooses or changes Known before starting the experiment. The factor that is intentionally changed by the investigator in an experiment There can be only one independent variable in an experiment Dependent Variable The factor that you measure or observe as data The factor that will change as a result of the independent variable This variable depends on the independent variable. There can be one or more dependent variables in an experiment

Constants The factors or conditions that are kept the same (unchanged) in an experiment Constants make sure you have designed a fair test There are many controlled variables in an experiment. Sometimes called controlled variables

Graphing Study Guide Complete the handout! Are you ready to go?

There are 4 major types of graphs we’ll use this year. I can remember that

Types of Data 1.Discrete data = consist of categories (days of the week, kind of animal, color) 2.Continuous data = consist of measurements involving a scale with equal measurements; a range of values (temperature, length of time in hours, height in centimeters)

Four major types of graphs 1.Pie chart/graph = consist of categories (display percentages) 2.Bar graph = used to represent discrete data; the IV is typically qualitative and DV is typically quantitative

Four major types of graphing 3. Line graph = used to represent continuous data, usually tracking changes over time; the IV and DV are both quantitative and the line connecting the points has meaning 4. Scatter plot = similar to a line graph, but the data points are NOT connected because a connecting line would have no meaning; a line of best fit might be constructed to show a trend in the data; IV and DV are typically both quantitative

Scatter plot This is a line of best fit – it is a straight line that comes as close to possible as all the data points The data points should NOT be directly connected because the IV is discrete

Bar Graph This is what we mean by discrete data – it’s a category and there’s no “middle value” between each category

Line Graph Each value here has meaning (I could determine Jill’s elevation at 3.2 hours) so I connect my data points with a line

Pie chart Here I have data organized in a percentage out of 100 – this is good way to represent it

A few final thoughts Scientists must represent their data graphically in a fair way that tells the most accurate story It is possible to change the scale of a graph to make it look like the data tells a much different story than the numbers actually show Additional labels might also be used to make the reader infer certain things from the same set of data

For example… At most, how different is the average rainfall from this year’s rainfall? This graph has been manipulated to make it look like there is a much bigger difference in rainfall than 0.4 cm Bad scientist!

A more accurate graph Good scientist!

Another Example Quarter, Year Image source: N umber of jobs (thousands) U.S. Jobs by Quarter What conclusions can you draw from this graph?

Here’s the same graph with a few extra labels… Image source: The data is the same but it could be used to create different inferences

Examples Question: Does changing the temperature of a ball affect the height the ball will bounce? What is the scientist changing? (independent variable) – The temperature of the ball What is the scientist measuring? (dependent variable) – Bounce height of the ball when dropped What should be kept the same or constant for a fair test? (constants) – Same ball – Dropped from same height – Onto same surface. – Etc. What type of graph should we use for this data? Discrete or continuous? SCATTER PLOT AND LINE OF BEST FIT

Question: Does changing the color of light change the growth rate of plants? Independent? – Color of light Dependent? – Growth rate of plants Constants? – Age of plant – Type of plant – Amount of light – Amount of water – When measured – Type of container – Etc. What type of graph should we use for this data? Discrete or continuous? BAR GRAPH