Variables in an experiment

DEPENDENT VARIABLE

• The dependent variable is the variable that is being measured in an experiment.

Independent

• The independent variable is the variable that is that is being changed in an experiment.

Examples:

• Dependent variable example:

• Independent variable example:

Controlled Variables

Controlled variables are variables that are variables that stay they same throughout an experiment.

• Some controlled variables for the above investigation might be:

Experimental Control

• An experimental control is a group of things in an experiment that is not exposed to the independent variable.

• This isolates the independent variable's effects on the experiment and can help rule out alternate explanations of the experimental results.

Experiment Control Example:

• An experimental control for the above investigation might be:

• For example, say you wanted to the amount of chemical it took to kill a group of flies you would expose flies to various amounts of the chemical and see how much it took to kill the flies.

• The experiment control would be to keep a group of flies in the same conditions as the flies exposed to the chemicals, but the experimental control group of flies would NOT be exposed to the chemical.

Practice time

Directions: For the following questions please,• Underline the dependent variable• Circle the independent variable• Pick 2 questions and write a hypothesis that

has a prediction AND a reason.

Practice question 1:

• How does the amount of television watched affect attention?

Practice question 2:

• How do carbon dioxide levels in the atmosphere affect global temperatures?

Practice question 3:

• How do different brands of fertilizer affect pea plants growth?

4. What brand of paper towel absorbs the most water?5. How does light intensity affect plant growth?6. How does the shape of an object affect the rate at

which it falls through water?7. How does slope angle affect speed?8. How does the weight of a bicycle affect coasting

speed?9. What type of rock is the most resistant to

weathering?10.How does the mass of a rock affect barnacle density?

11. How do plants affect dissolved oxygen levels in an aquarium?12. How does the surface area of a paper airplane’s wings affect

flight distance?13. How does wind affect the distance different sized particles

(sand, gravel, rock) can travel?14. What place at SQHS has the most bacteria? 15. Does environment determine the stem color of a fast plant?16. How does the length of a lever affect the force that must be

applied to lift an object?17. How does wind direction in Bellingham affect the temperature?18. How does camouflage affect the survival of a species?19. How is the rate of starch breakdown affected by different

people’s saliva?

20. How does gender affect the average carapace size of a Dungeness crab?21. How do varying amounts of catnip affect cat behavior?22. What affect does salt placed on roadways to melt ice have on plants

living on the shoulder?23. Does what a chicken eats affect the level of cholesterol in its eggs?24. Does repetition increase the speed in which a mouse can navigate a

maze? 25. What affect does the color of light have on plant growth?26. How does the amount of fertilizer applied to a plant affect its growth?27. How does the size of a crab affect its speed?28. What type of mouthwash is most affective in killing mouth bacteria?

Scientific questions should:

• Include both the independent and dependent variables• Be written in a question format• Be based on an observation.

Practice

• 1. Caffeine may affect your heart rate.

Practice

• 2. Use of fertilizers may be causing frog mutations.

Hypotheses should:

• Have a prediction and a reason.• Be based on a scientific reason/ observation.• Never be thought of as _guess – only.• State both a prediction and a reason.

Hypothesis practice

• Write a hypothesis for the question that you wrote about caffeine affecting heart rate.