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Scientific MethodScientific Method

Writing a Purpose StatementWriting a Purpose Statement

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What is a Problem Statement?What is a Problem Statement?

The question that you select for The question that you select for your investigation – the basis of your investigation – the basis of your experiment. your experiment.

The research and experiment The research and experiment you will be conducting center you will be conducting center around finding an answer to the around finding an answer to the question or problem statement. question or problem statement.

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A A Good Problem Statement Good Problem Statement (or Purpose)(or Purpose) The problem statement only needs to be The problem statement only needs to be

one sentence longone sentence long..

The problem statement is The problem statement is alwaysalways in the in the form of a form of a questionquestion..

Should be Should be open-endedopen-ended (not answered by (not answered by yes or no)yes or no)

A problem statement A problem statement includes what is includes what is changedchanged (independent variable) and (independent variable) and what is what is measuredmeasured (dependent variable). (dependent variable).

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A Good Problem StatementA Good Problem Statement

How does light affect the reproduction How does light affect the reproduction of bread mold on white bread?of bread mold on white bread?

Note the question is about:Note the question is about: one life processone life process one type of moldone type of mold one type of bread one type of bread one factor that affects it growthone factor that affects it growth

(reproduction)(bread mold)(bread mold)(white bread)(white bread)

(light)(light)

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A Poor Problem Statement A Poor Problem Statement

How does light affect molds?How does light affect molds?

Note the question would have to test:Note the question would have to test: all the life processes of moldall the life processes of mold all types of moldall types of mold all types of growth mediums all types of growth mediums one factor that affects its growth (light)one factor that affects its growth (light)

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Choose a problem that can be Choose a problem that can be solved experimentallysolved experimentally

Look at each question below and evaluate. Is it an example of a good or poor problem statement? Explain why.

What is mold? Poor problem statement because it can be answered by

finding the definition of the word mold in the dictionary.

Will a green plant stay green if grown in the dark? Poor problem statement because it can be answered by

a yes or no.

How does temperature affect the growth rate of bread mold on white bread? Good problem statement because it can be answered

by experimentation.

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Independent VariableIndependent VariableThe experimenter changes only one

variable in an experiment.

This is important so we can see the effect of changing that variable.

The variable that is changed is called the independent variable (test).

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Dependent VariableDependent Variable The experimenter measures or observes the change

caused by the independent variable.

The variable that is measured or observed is referred to as the dependent variable (outcome).

As a result of changing the IV

The measure should include the units of measurement. (i.e., count, percentage, length, width, weight, voltage, velocity, energy, time)

If the experimenter observes the change, then the observed variable should be obvious. (i.e., color change, lights on in one trial, then lights off in another trial)

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Good Problem StatementsGood Problem StatementsPractice identifying Practice identifying

independent and dependent variables.independent and dependent variables.

Question Independent Variable(What is changed?)

Dependent Variable(What is measured?)

Water faucet Water faucet opening opening (closed, half open, (closed, half open, fully open)fully open)

Amount of water Amount of water flowing measured flowing measured in liters per minutein liters per minute

Amount of fertilizer Amount of fertilizer measured in measured in milliliters (mL)milliliters (mL)

Growth of the plant Growth of the plant measured by measured by increase in mass increase in mass measured in gramsmeasured in grams

How much water flows through a faucet at different openings (closed, half open, fully open)?

How does the amount of fertilizer affect the growth of a tomato plant (as measured by an increase in mass)?

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Question Independent Variable(What is changed?)

Dependent Variable(What is measured?)

The group receiving The group receiving the survey: the survey: teenagers or teenagers or parentsparents

The amount of time The amount of time each person watches each person watches television per day television per day measured in hoursmeasured in hours

Voltage of the Voltage of the electricity electricity measured in voltsmeasured in volts

Speed of rotation Speed of rotation measured in measured in revolutions per revolutions per minute (RPMs)minute (RPMs)

Good Problem StatementsGood Problem StatementsPractice identifying Practice identifying

independent and dependent variables.independent and dependent variables.

Who watches television the most in a day: teenagers or their parents?What effect does increasing the voltage have on the rotation speed of an electric motor?

Identifying purpose statements & variables

1. Which problem statement is worded the best?

1. 2. 3. 4.

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1. Does boiling an egg change its mass?2. How does boiling an egg affect its mass?3. What effect does boiling have on an egg?4. Is mass changed when you boil an egg?

2. What would be the independent variable in this problem statement: “How does the position in which a seed is planted affect how quickly it sprouts?”

1. 2. 3. 4.

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1. The amount of time it takes to sprout2. The number of seeds planted3. The position in which seeds are planted4. The height of the sprouted plant

3. What would be the dependent variable in this problem statement: “How does the position in which a seed is planted affect how quickly it sprouts?”

1. 2. 3. 4.

0% 0%0%0%

1. The amount of time it takes to sprout2. The number of seeds planted3. The position in which seeds are planted4. The height of the sprouted plant

4. True or False: A good problem statement should always be worded so it can be answered by yes or no.

1. 2.

0%0%

1. True2. False

5. True or False: A good problem statement should always be worded as a question.

1. 2.

0%0%

1. True2. False

6. What would be the dependent variable in this problem statement: “Which food (apple, potato, or tomato) will produce the highest amount of energy measured in voltage?”

1. 2.

0%0%

1. The amount of energy 2. The type of food (apple, potato, or tomato)

7. What would be the independent variable in this problem statement: “Which surface (grass, sidewalk, road) will the RC car have the fastest speed over a distance of 10 meters?”

1. 2.

0%0%

1. Speed of RC car over 10 meters2. The type of surface (grass, sidewalk, road)

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Now, pick 1 bad problem statement and re-write it to make it better. Use the following templates or your own:

What is the effect of (a) on (b)? How does (a) affect (b)? In what way does (b) depend on (a)? Which (a) will (b)?

(a) - is the independent variable(b) - is the dependent variable