Independent Variable
Define the independent variable.
The independent variable is what we manipulate in the experiment or purposefully change.
Define the dependent variable.
The dependent variable is the variable we measure as a result of what we manipulate (independent variable). You can also think of it as the variable can change as a result.
*It may be the case that the dependent variable does not change as a result (the value may not be affected), sometimes we say that it is measured as a result of our manipulation.
Define the controlled variable.
The controlled variable is the variable that does not change over the course of the experiment or is held constant.
For both of the experiments we have looked at from the packet, determine the independent variable:
- Alka-Seltzer Experiment
- Boiling Points of Alcohol Experiment
- Alka-Seltzer Experiment - NUMBER of alka-seltzer tablets
- Boiling Points of Alcohol Experiment - type of alcohol/formula of alcohol/number of carbons in an alcohol
For both of the experiments we have looked at from the packet, determine the dependent variable:
- Alka-Seltzer Experiment
- Boiling Points of Alcohol Experiment
- Alka-Seltzer Experiment - FINAL temperature of the vinegar mixture
- Boiling Points of Alcohol Experiment - Boiling Point (BP) of the alcohol
For both of the experiments we have looked at from the packet, determine the controlled variable:
- Alka-Seltzer Experiment
- Boiling Points of Alcohol Experiment
Alka-Seltzer Experiment
- Volume of vinegar
- Room pressure
- Initial temperature of vinegar
Boiling Points of Alcohol Experiment
- Room Pressure
- Volume of alcohol
In an experiment, you can have at most ____ independent variable(s).
1
In an experiment, you can have at most ____ dependent variable(s).
1
In an experiment, you can have at most ____ controlled variable(s).
As many as needed (infinite)
How did we know with certainty that the independent variable was the number of tablets and NOT the final temperature or any other variable for the Alka-seltzer experiment?
For the experiment to proceed, we only had a few options of the start we could manipulate and the final temperature is the temperature measured ONLY after the tablets were thrown in. All other variables were held constant, so we didn't purposefully change them. We can't manipulate the final temperature to get a different number of tablets -- so by process of elimination, the number of tablets if the independent variable.
How did we know that the dependent variable is the boiling point and not any other variable in the Boiling Point of Alcohol experiment?
We can ignore the room pressure and volume of vinegar as they are both held constant, so they are not changing as a result.
We can treat alcohol name/formula/number of carbons to be different alcohols with different number of carbons. For us to complete the experiment, we would need place a different alcohol on a hotplate at 75 mL using a volumetric container (beaker/graduated cylinder/Erlenmeyer Flask), we place it on a hotplate with a thermometer. The moment we see bubbles or hear/see sizzling, we record the temperature on the thermometer. The only variable we can measure as a result of our manipulation is the boiling point.
Why do we need controlled variables?
Controlled variables help to ensure that if there is a change happening to the dependent variable, that the independent variable is responsible for it.
Consider the case of the Alka-Seltzer experiment, suppose that we allow the volumes of the vinegar to be different values and received the same results for everything else. Can we say that the number of tablets is responsible for the changes to the final temperature?
See the following:
Students in physics class are asked to find the determine the following question:
Will changing the length of a pendulum (string with a weight at the bottom) affect the time it takes for one pendulum swing?
Watch the segment between 0:49 to 0:54 in this video to see how a pendulum is operated: https://www.youtube.com/watch?v=eBNPPz8bQzc
What is the dependent variable measured in this experiment according to the experiment above?
Time it takes for a length of a pendulum swing
See the following:
Students in physics class are asked to find the determine the following question:
Will changing the length of a pendulum (string with a weight at the bottom) affect the time it takes for one pendulum swing?
Watch the segment between 0:49 to 0:54 in this video to see how a pendulum is operated: https://www.youtube.com/watch?v=eBNPPz8bQzc
What is the dependent variable measured in this experiment according to the experiment above?
Length of a pendulum
See the following:
Students in physics class are asked to find the determine the following question:
Will changing the length of a pendulum (string with a weight at the bottom) affect the time it takes for one pendulum swing?
Watch the segment between 0:49 to 0:54 in this video to see how a pendulum is operated: https://www.youtube.com/watch?v=eBNPPz8bQzc
What is the controlled variable measured in this experiment according to the experiment above? Name at least 2.
The question tells you the two variables that CANNOT be chosen:
"Will changing the length of a pendulum (string with a weight at the bottom) affect the time it takes for one pendulum swing?"
It is shown from the question that they plan to manipulate the length of the pendulum (independent variable) and they plan to measure the time it takes for a pendulum swing (dependent variable).
ANY variable that can get in the way of that could be a controlled variable -- for example the weight at the end of the pendulum, the angle that you release the pendulum before it swings, the type of string used for pendulum, etc.) We hold them constant so as to ensure that we are able to answer that question.