#11 Variables, Controls, Constants and Graphing Variables

Variable  Any factors that can change during an experiment (it varies).  There are two types – Dependent – Independent

Independent variable  (A manipulated variable in an experiment whose presence determines the change in the dependent variable.)  The one that I decide to change or determine.  What is being tested out ex: how many skittles, how much water  Place on x-axis.

Dependent variable  (The observed variable in an experiment whose changes are determined by the presence of the independent variables.)  What you are recording as your D ata.  What is being measured ex: work rate, plant height ex: work rate, plant height  Place on the y-axis

Constants & Controls  Constant – the factors that are kept the same in an experiment to make sure the experiment is valid and controlled (stays the same)  Control – the measurements that are recorded as a basis for comparing the results (what’s “normal”).

Example:  You are doing an experiment to see if eating ice cream in the morning will help you run a mile any faster. The first morning you eat half a tub of Ben &Jerry’s before you start running. The second morning you eat an entire tub before you begin (watch out for cramps!)  What would be the independent variable & dependent variable?  What would remain constant and what would be the control?

Answer:  Independent variable (I decide it changes) = How much ice cream. = How much ice cream.  Dependent variable (Data, what’s measured) = Running time for a mile = Running time for a mile  Constant (Stays the same) = distance, type of ice cream, time of day, same person, same shoes, ice cream vs. other sweets, same amount of sleep, etc.  Control (What is “normal”) = usual running time for a mile without any ice cream at all.

Bar Graphs  Good for comparing data  Specific #’s of specific things

Circle Graphs (Pie Charts)  Shows how parts relate to the whole.  Often used for percentages. (The whole pie = 100 %) (The whole pie = 100 %)

Line Graphs  Used to demonstrate continuous change  Used to demonstrate continuous change  The slope of a linear graph (a straight line) is constant (y=kx) (a straight line) is constant (y=kx)

Graphing Variables  Two variables may have: –a strong relationship, –a weak relationship, –or no relationship at all.

 In a direct relationship, when one variable increases, the other also increases.  This graph also shows a linear relationship (it is a straight line)  In an inverse relationship, when one variable increases, the other decreases.

Complex Relationships  Some relationships are neither direct nor inverse.  This graph shows a non- linear relationship.

Draw This REALLY BIG in your spiral / binder