The Scientific Method:

A look at the experimental variables and a hypothesis

What is an “experiment?

• In school “experiment” often gets applied to any hands on activities.

• We have not completed any true experiments so far this year.

• We will have several hands on experiences but only a few experiments.

What is a true “experiment”?

• A science experiment tests a hypothesis following a procedure or set of steps

• In order to write a hypothesis you need to understand experimental groups and variables

Experimental Groups/ConditionsManipulated group (M)(aka manipulated condition)• It is what you are testing to

see if it has an effect• You test only one variable at

a time • Has the manipulated

variable applied to it

Sometimes called the test condition or group as well

Control group (C)(aka control condition)

• The group that does not have the manipulated variable applied to it

• Used to compare to the manipulated

• If there is a difference between the manipulated and the control then the manipulated variable influenced the results

Does Miracle-Gro® make a plant grow taller?

Experimental Question:

What would the experimental conditions be?

Manipulated Condition• Applying Miracle-Gro®

fertilizer to plants

Control Group• Plants that do not have

Miracle-Gro® applied to them

Experimental Variables

In order to set up the experimental groups you need to understand the variables:• Manipulated• Responding• Standardized (sometimes called controlled

variables)

Manipulated Variable (MV)

• This is what the experimenter changes to see if it has an effect

In the Miracle-Gro® experiment what is our manipulated variable?

Responding Variable (RV)

• This is what you will measure• It is called the responding variable because it

is the “response” you expect to get from the change you made

• You can use both qualitative and quantitative observations to observe the response

What would the responding variable be?

Standardized Variables (SV)

• These are all of the things that are kept the same between the test groups/conditions in the experiment

What should the standardized variables be in this experiment?

What is a hypothesis?

A prediction of what you think will happen as a result of the changes you made in the experiment:• Do you think the manipulated variable will

have an affect?• How do you think it will affect the responding

variable?

How to write a hypothesis

• You need to write your hypothesis in an if, then, because statement

If….

• The if part of your statement should explain to your reader the experiment setup. It needs to answer the following:

• What is your manipulated group?• What is your control group?

Example: If we apply miracle grow fertilizer to half of the plants and no fertilizer to the others

Then….

• The then part of your statement explains what you think will happen

• You should explain what you expect to see in terms of the responding variable.

Example:Then the plants that have the fertilizer will grow taller than the plants that do not have fertilizer

Because…• Your hypothesis should be an educated guess• The because part of the statement explains or

justifies why you believe the experiment should turn out in this way

• It should be based on prior knowledge or research

Example: Because miracle is advertised to make plants grow taller

Putting the parts together

If we apply miracle grow fertilizer to half of the plants and no fertilizer to the others Then the plants that have the fertilizer will grow taller than the plants that do not have fertilizerBecause miracle is advertised to make plants grow taller