Identifying Variables and writing a Hypothesis

pages 33-35

If grades are related to paying attention then I should get an A if I listen

Grades are the observed or measured variableDependent

Listening is the changed or tested variable.Independent

What would be some of the needed Control Variables?

What do you think the difference is between a testable question and a hypothesis?

Testable Question: This is a question that we would be able to perform an experiment to answer.

What I want to find out about.

EX. Does changing the height from which a basketball is dropped affect how high it bounces?

Hypothesis: This is your guess (what you think) will happen if you perform an experiment.

What I think will happen.

EX: If the height a ball bounces is related to the height from which a basketball is dropped then If it is dropped from a higher position it will bounce higher.

Identifying the Variables• Lets say we wanted to test our testable

question and determine if our hypothesis was correct:– Testable ?: Does changing height from which a basketball is dropped

affect how high it bounces?– Hypothesis: If the height a ball bounces is related to the height from

which a basketball is dropped then If it is dropped from a higher position it will bounce higher.

• Independent: What I am testing (I control this)– Height the basketball is dropped from.

• Dependent: What I am measuring – Height the basketball bounces

• Control: The things that are kept the same– Same ball, amount of air, the person or machine doing the

dropping, location, temperature, weather, routine, etc….

It all starts with a question…

• Not just any question:– A testable question:

• Meaning that the question is written in a way that an experiment can be performed and a result obtained.

– Example• Bad: Do Guinea pigs like light?• Good: Does changing the amount of light in a

Guinea pigs environment affect the amount of time it spends playing?

Then What?

• We must now develop an experiment to test our testable question.– STEPS

1. Identify our variables.

2. Write our hypothesis.

3. Design and conduct our experiment.

Independent variable(there can be ONLY 1 “Cause”)

• Also referred to as the manipulated or experimental variable. – This means the thing that we alter, change, or test

• Examples: amount of food, water, air– The amount of medicine, sunlight

Dependent variable(s)(1 or more “effect”)

• Also called the responding variable because they rely on something else to happen– This is the thing we measure or observe

• Examples: amount of growth, forming a disease, rise in temperature (due to something)

Control variables(many)

• All other variables must be kept the same in order to make sure the item being tested (independent) is the cause, of what happened “the effect” (dependent).

• Why?– We want to only test one variable at a time (independent

variable).• If more than one thing changes we will not know the

reason our results have changed– However, We may observe more than one (dependent) at a

time• Example:

– (growth rate (how fast) and overall height)

Controlled (Valid) Experiment• A controlled experiment is one in which there is

only 1 independent variable changed.

• This allows us to compare data (analyze) and to form a conclusion.– If done correctly we will be able to confirm or

disprove our hypothesis.• It is ok for your hypothesis to be wrong, you still learned

something.• Two types of Validity:

– Internal: Did you do the research correctly

• (follow the scientific method)

– External: Can this information be applied on a larger scale and/or repeated

• (What can we do with it?)

How do I decide which is which?

• The independent variable answers the question "What do I change or test?".

• The dependent variables answer the question "What do I observe or measure?".

• The control variables answer the question "What do I keep the same?".

Identifying Variables and Using them within a graph

• Remember your “ DRY MIX”

• DRY = Dependent, Responding, Y-axis

• MIX = Manipulated, Independent, X-axis

X-Axis

Y-Axis

Independent(Cause)

Dependent(Effect)

DRYMIX

TITLE: Independent (X) (cause) VS. Dependent (Y) (effect)

Always Remember your “ID”

I.D. = Independent

vs. Dependent

Using the variables, observations, and inferences to make a hypothesis.

1. The students are doing an activity about a candle burning.

2. They observe that the candle burns when there is AIR.3. They infer that a candle must need oxygen to burn.4. They form a question “Will a candle burn without oxygen?”

5. They develop a testable question1. “ Does changing the amount of oxygen available to a

candle affect how long it burns?”

6. They must identify the variables and decide what to test (in = amount of oxygen, dep = how long the candle burns, con = candle type, size, shape, color, location etc…,)

7. Finally they work to form the hypothesis.What you THINK will happen in the lab.

Hypothesis - Format

• If __dependent_ is related to _independent_ then _prediction_ will happen.

• In other words – If the thing I observe is related to the thing I change

then something I think will happen.

• Using our information that would mean they would come up with– If a candle burning is related to the amount of oxygen

then a candle with less oxygen will go out quickly.

Thinking about variables a different way Cause and Effect

• When we do an experiment we want to find out if changing one thing causes another thing to change. – Example: Does changing the amount of water a

plant gets affect how fast it grows?• The CAUSE in the lab is the thing we are changing

(INDEPENDENT)• The EFFECT that we are looking for is the

(DEPENDENT)• Therefore if we re-wrote our hypothesis format using this

idea it would be – If the EFFECT is related to the CAUSE then I think

PREDICTION will happen.

Practice making a hypothesis: ExampleDirections: Circle dependent, underline independent then write the hypothesis

1. Chocolate may cause pimples

Now use our format:

If __dependent_ is related to _independent_ then _prediction_ will happen.

If________________are related to __________________then

a person eating more chocolate will have more pimples.• Could also use

– more choc, less pimples– Less choc, more pimples– Less choc, less pimples

Chocolate pimples

Practice making a hypothesis:Directions: Circle dependent, underline independent then write the hypothesis (use those 3 questions)• 1. Texting may cause accidents• 2. Salt in soil may affect plant growth• 3. plant growth may be affected by the

color of the light• 4. Bacterial growth may be affected by

temperatures• 5. Ultraviolet light may cause skin cancer• 6. Temperature may cause leaves to

change color.

AnswersNow use our format:

If __dependent_ is related to _independent_ then _prediction_ will happen.

1. Texting may cause accidents

If accidents are related to texting then a person texting a small amount will have more accidents.

2. Salt in soil may affect plant growth

If plant growth is related to amount of salt in the soil then soil with a lot of salt will cause a plant to grow less.

Answers CONT.. Now use our format:

If __dependent_ is related to _independent_ then _prediction_ will happen.

3. plant growth may be affected by the color of the light

If plant growth is related to color of light then Green light will cause a plant to grow less.

4. Bacterial growth may be affected by temperatures

If bacterial growth is related to temperature then higher temperatures will increase bacterial growth.

Answers Cont… Now use our format:

If __dependent_ is related to _independent_ then _prediction_ will happen.

5. Ultraviolet light may cause skin cancer

If skin cancer is related to Ultraviolet light then skin exposed to more ultraviolet light will have more skin cancer.

6. Temperature may cause leaves to change color.

If leaves changing color is related to the temperature then higher temperatures will cause less change in leaf color.