Three Types of Experimental Variables

Name: Class: Date:

An experiment may have many variables. The purpose of this activity is to identify and define the three types of variables in an experiment.

Three Types of Variables

1.  Manipulated Variable—The part, or factor, of the experiment that is intentionally changed by the investigator in an experiment. There will be only one manipulated variable in a valid experiment.

2.  Responding Variable—The part, or factor, of the experiment that is affected because of the change (manipulated variable)—it is can be measured. Several variable may respond to the manipulation. Generally, an experiment is concerned with only one.

3.  Controlled Variable(s)—The parts, or factors, that remain the same (kept constant) in an experiment.

Example: An experiment was done to see if adding coffee to the water you feed a plant increases the growth of the plant. The variables are identified below:

Manipulated Variable: Coffee (could be amount or brand, but not both at the same time)

(What was changed by the investigator?)

Responding Variable: Growth of plant

(What might be affected by the change?)

Controlled Variables: Type of plant, amount of sunlight, amount of liquid given, type of soil, etc…

(What needs to stay the same?)

Hypothesis: If (manipulated variable) then (responding variable).

Directions: In each of the following experiments:

1.  Identify the manipulated variable

2.  Identify the responding variable

3.  Identify at least three (3) variables needing to be held constant/controlled.

4.  Write an if-then hypothesis statement. (If (manipulated variable) then responding variable).

5.  Label the x- and y-axes, as if the data would be graphed. No graphing is necessary.

1.  An experiment is conducted to determine if the weight of a ball affects the speed at which it rolls down a slide.

Variable / Answer
Manipulated
Responding
Controlled (3 qty)
(kept constant)
Hypothesis:

2.  An experiment is conducted to determine if the number of practice problems affects the score on a math exam.

Variable / Answer
Manipulated
Responding
Controlled (3 qty)
(kept constant)
Hypothesis:

3.  An experiment is conducted to determine if the amount of sunlight a plant receives affects its growth.

Variable / Answer
Manipulated
Responding
Controlled (3 qty)
(kept constant)
Hypothesis:

4.  An experiment is conducted to determine if the brand of paper towels affects the amount of water it can absorb.

Variable / Answer
Manipulated
Responding
Controlled (3 qty)
(kept constant)
Hypothesis:

5.  An experiment is conducted to determine if the foods given to a chicken affects the number of eggs it lays.

Variable / Answer
Manipulated
Responding
Controlled (3 qty)
(kept constant))
Hypothesis:

KEY

Problem 1:

Variable / Answer
Manipulated / Ball Weight
Responding / Ball Speed
Controlled
(kept constant) / Release position of ball, slope of slide, size and type of ball…
Hypothesis: If the ball’s weight is increased then the ball speed increases.

Problem 2:

Variable / Answer
Manipulated / Number of Practice Problems
Responding / Score on Math Exam
Controlled
(kept constant) / Number of questions on exam, types of problems, allotted time for completion, subject taking exam
Hypothesis: If the number of practice math problem for an exam is increased then the math score exam increases.

Problem 3:

Variable / Answer
Manipulated / Amount of Sunlight
Responding / Plant Growth
Controlled
(kept constant) / Type of plant, surroundings, soil, amount of water
Hypothesis: If the amount of sunlight a plant receives is increased then plant growth increases.


Problem 4:

Variable / Answer
Manipulated / Paper Towel Brand
Responding / Amount of Water Absorbed
Controlled
(kept constant) / Size of paper towel, amount of water, allotted time
Hypothesis: If towel brands are changed then the amount of water absorbed by each towel changes. (Conclusion: Brand X performs better than Brands Y and Z.)

Problem 5:

Variable / Answer
Manipulated / Food Types
Responding / Number of Eggs Laid
Controlled
(kept constant) / Surroundings, health of chickens, frequency of feedings, chicken statistics
Hypothesis: If a chicken’s food type is changed then the number of eggs laid changes. (Conclusion: Food A produces better results than Foods B and C.)