How to identify the variables in an experiment
DV = Dependent variable (the variable that you are trying to see what will happen to it if you do something to it). This is listed on the Y-axis of a graph.
Example: How far will a ruler bend if you do ____ to it.
IV = Independent variable (the variable you do to the DV to see if it will change it). This is listed on the x-axis of a graph.
Example: Putting a mass at the end of a ruler and increasing the mass.
Example: Keeping the mass constant, but moving it along the ruler.
CV = Controlled variable (the variable that you will keep constant).
Example: Length that the ruler sticks out over the table.
Example: Mass on the ruler.
NOTICE: Sometimes, the IV for one is the CV for the other!
NOT an example: Keeping the temperature the same, air pressure…etc (yes, these are "controlled", but they wouldn't affect the outcome)
Constants: These are not variables, but rather they are important factors that are held constant. For example: If you were doing an experiment with plant growth and you were using tomato plants, you would use the same type of plants for each experiment. This is a constant. It is NOT a controlled variable, but it is a constant.
Some other constants - that are not important because they don’t affect the outcome of this experiment are: Air pressure, temperature of the room…etc. So, don't mention these! There are an infinite amount of "constants". Only mention those that could affect the results if they were changed.
Read the following experiments and then write the DV, IV, CV and identify any important constants:
Experiment #1:
A coffee can full of water has a hole placed in the bottom of it and the time it takes for the water to leak out is recorded. This experiment is repeated with increasing hole sizes but the same amount of water to begin with. In each experiment, the time it takes for the water to leak out is recorded.
DV______
IV ______
CV ______
Important Constants______
Experiment #2:
Rubber balls of different sizes but the same mass are dropped from the top of the building. The height that the balls bounce up to (on the first bounce) is recorded.
DV______
IV ______
CV ______
Important Constants______
Experiment #3:
Rubber balls of different mass but the same size are dropped from the top of the building. The height that the balls bounce up to (on the first bounce) is recorded.
DV______
IV ______
CV ______
Important Constants______
Experiment #4:
Five bubble solutions are made and placed in 5 cups of the same size. The solutions are made with varying amounts of soap and water (some have more water than soap, others have more soap than water. The exact amount of soap:water ratio is recorded). A straw is used to blow bubbles - the same straw. The experimenter puts the straw into each cup (one at a time) and blows into the straw with equal force and for the same amount of time for each cup. When the experimenter is done, they count the number of bubbles made.
DV______
IV ______
CV ______
Important Constants______
How to title your graphs
Graphs are always titled: y vs. x.
Example: Distance vs. time
Distance is on the y-axis. Time is on the x-axis.
Example: Time vs. Force
Time is on the y-axis. Force is on the x-axis.
Graphs are always titled: Dependent variable vs. Independent variable
Therefore: The variable on the y-axis is the DEPENDENT VARIABLE
The variable on the x-axis is the INDEPENDENT VARIABLE
You should always list on your graph, somewhere under the graph, what the CONTROLLED Variable is.
Example: In the ruler lab, the dependent variable is how far the ruler bends. The independent variable might be the amount of mass placed on the end of the ruler. The controlled variable would be the placement of ruler over the edge of the table.
Graph Title: Deflection of ruler vs. Mass at the end of the ruler.
Controlled Variable: The ruler hangs 0.5 meters over the edge of the table. (write this somewhere underneath the graph so it is clear what is the CV).