A Controlled Experiment



Name___________________________________________ Variable Practice

Example:

I want to study plants and figure out a way to make them grow faster.  There are a lot of factors that I think may play a role in plant growth.  However, since I am doing a controlled experiment, I only want to manipulate one variable at a time.  After making observations and conducting some research, I have decided that I think that the amount of light a plant receives affects the rate at which it grows.  Therefore, the amount of light that the plant receives is going to be my independent variable.  As I change the amount of light that the plants get, it may grow more, it may grow less, or growth rate may not change.  This would be my dependent variable.  As I plan my experiment I need to keep several things in mind.  First of all, I know that plant type, amount of water, and amount of fertilizer could also affect the rate at which my plants grow.  But, in this particular controlled experiment I am not testing those variables.  Therefore I need to make certain that each plant is the same type, that each receives the same amount of water, and that each receives the same amount of fertilizer.  (I can always do more experiments later to determine how each of these affects plant growth.)  Also, I need to think about how I am going to measure light amount and plant growth, so I need to form operational definitions.  For instance, I might measure how many hours/day that the plant receives light or what the watt of the light bulbs are.  I might measure plant growth in centimeters/day or in number of new leaves/day.

Independent variable – What are you manipulating and testing?

Dependent variable – What results are you looking for or what are you going to measure?

Controlled variables – Everything that stays the same

Example 1. Students want to measure if their assigned seat really affects their socializing in class.

Independent variable: Where the students sit

Dependent variable: How much the students socialize

Controlled variables: Same students, same class, same time of day, same activities

Operational definition (how might you measure the dependent variable?): number of times teacher has to ask students to stop talking

 

Example 2. Teachers wanted to study if hours of sleep affect the attentiveness of students in class.

Independent variable: The number of hours of sleep the kids get

Dependent variable: How attentive the students are

Controlled variables: Same students, same class, same time of day, same activities

Operational definition (how might you measure the dependent variable?): students rank how alert they feel on scale of 1-10

 

Now you try…

1.  Students want to measure if the type of desk you sit in affects your ability to pay attention.

Independent variable:

Dependent variable:

Controlled (list 3):

Operational definition (how might you measure the dependent variable?):

  

2.  Teacher wants to measure if the number of times homework is not turned in affects science grades.

Independent variable:

Dependent variable:

Controlled (list 3):

Operational definition (how might you measure the dependent variable?):

 

3.  Teachers want to measure if years of schooling affect the salary of business people.

Independent variable:

Dependent variable:

Controlled (list 3):

Operational definition (how might you measure the dependent variable?):

  

4.  Students wanted to study if the hours of sleep teachers get affect their level of patience with students.

Independent variable:

Dependent variable:

Controlled (list 3):

Operational definition (how might you measure the dependent variable?):

5. Students want to measure if the time of day affects tricks learned by a dog.

Independent variable:

Dependent variable:

Controlled (list 3):

Operational definition (how might you measure the dependent variable?):

6. Two groups of students from the same class were tested to compare their speed working math problems. Each group was given the same problems. One group used calculators and the other group computed without calculators.

Independent variable:

Dependent variable:

Controlled (list 3):

Operational definition (how might you measure the dependent variable?):

7. A study was done to determine if different tire treads affect the braking distance of a car.

Independent variable:

Dependent variable:

Controlled (list 3):

Operational definition (how might you measure the dependent variable?):

8. Does the amount of sugar in a can of soda affect how much energy a person has after drinking the soda?

Independent variable:

Dependent variable:

Controlled (list 3):

Operational definition (how might you measure the dependent variable?):

9. What is the importance of doing controlled experiments? Why don’t we test several variables at one time?

10. Why is it important to do multiple trials and average the data?

11. How do you average data?

12. What format will we use to write all of our hypotheses in?

13. What is the format for a scientific conclusion (see your red divider):

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