SCIENTIFIC METHOD

By Moira Whitehouse PhD

Complemented by my slideshow Scientific Method Procedures

1. One way scientists find out about the world around us.

The scientific method is

2. Also a procedure scientists use to answer specific questions.

VARIABLE

In order to understand the Scientific Method, we first need to understand what a

is

A variable is

anything in an experiment that can change.

Here you see a car sitting on top of a ramp.

What could you change about this car or ramp that might affect its speed?

So you need to know what things affect how fast a car will roll down a ramp.

You want to design a car that will roll down a ramp really fast.

Yes, what could you change or do to make the car go faster.

These ideas all make up something we call:

variables

There are three main kinds of variables

1. The change variable

2. The responding variable

3. The control variables

Let’s look more closely at these three kinds of variables

Remember the first is called

the change variable.

1. The change variable is:

• The variable that the experimenter changes on purpose.

• There can only be one change variable in any experiment.

• May also be called the independent variable. (two names for the same variable)

In the experiment on the next page, identify the change variable—what is the one thing the experimenter changed with plant 1, 2 and 3?

No Water

Plant 1 Plant 2 Plant 3

20 mL

Water every day

40 mL

Water every day

Yes, the experiment changed the amount of water that the plant receives each day.

The second type of variable is

2. The responding variable

2. The responding variable is

• What is measured or observed by the experimenter to see if the change variable caused a different result.

The responding variable is sometimes called the dependent variable. (again, two names for the same variable)

How this variable responds (goes faster, grows taller, warms up more, etc.)

depends on the change (or

independent) variable.

Let’s look again at the experiment where the amount of water each plant received was changed.

What could the experimenter observe or measure to see if the amount of water made a difference to the health of the plant?

No Water

Plant 1 Plant 2 Plant 3

20 mL

Water every day

40 mL

Water every day

The experimenter could have, for example, counted the number of green leaves on each plant or he could have measured the height of the plants after 14 days.

Some examples of responding variables in different experiments—things to be observed or measured are:The amount of water absorbed by two different brands of paper towels.

How far a ball rolls from different ramp angles.

The amount of feed eaten at a bird feeder in response to the type of seed in the feeder.

Whenever possible the experimenter should measure, instead of just observing, the responding variable.

In order to measure the responding variable the experimenter uses tools such as

a metric ruler or meter stick

To measure how far something moved.

balance scale

to measure the mass of something

thermometer

To measure how hot or cold something is

What might the change variable be in this experiment on water evaporating?

without fan with fan that moves the air

What could be the responding variable in this experiment? Remember you should measure.

PLASTIC CUP OF HOT WATER

STYROFOAM CUP OF HOT WATER

What might the change variable be in this experiment on keeping water hot?

What might be the responding variable in this experiment? Remember you should measure.

What would the change variable be in this experiment on how much heat different soils absorb?

What could be the responding variable in this experiment? Remember you should measure.

To use the scientific method to answer questions, we set up an experiment that changes just one thing and then we measure how that one change affects what we are interested in.

The question is always “what is the effect of change variable on responding variable”?

For example, in the case of our watering plants experiment, the question might be:

How does the amount of water you give a plant (change variable) affect how tall the plant grows. (responding variable)?

But there is more. In every experiment there is a third kind of variable called the control variable. Control variables are all those things in an experiment that you do not let change.

• Control variables must be kept constant between trials.

• There may be many control variables in any experiment

• A control variable is any other variable (other than the change variable)

that might affect the outcome of the experiment.

Think back to our experiment asking the question: “How does the amount of water affect how tall the plant grows in 14 days?”

What variables, other than the amount of water, could affect how tall the plant grows?

No Water

Plant 1 Plant 2 Plant 3

20 mL

Water every day

40 mL

Water every day

Things that might affect how tall the plant grows could include:

1. the amount of light 2. the temperature of the air3. the kind of soil

What would be the problem if we changed both the amount of water and the type of soil the plant is growing in at the same time?

Sure, you wouldn’t know if the growth was due to the water or the type of soil.

Plant 3Plant 1 Plant 2

20 mL

Water every day

No Water40 mL

Water every day

Sandy soil Clay soil Potting soil

Suppose the plant in the potting soil that was given 40 mL of water daily grew the tallest after 14 days?

Could we know whether the 40 mL of water or planting the plant in potting soil had caused the results?

Probably not: In order to make correct conclusions when doing experiments we must:• have only one change variable and• control all other variables that might affect the results—keep them constant through out the experiment.

Yes, you would have to plant all plants in the same potting soil, use the same kind of pot, expose all plants to the same amount of light and keep the air temperature the same.

Now, you want to find out if making the angle of the ramp higher would make the car coast further.

So let’s look at that toy car on the ramp again.

So your question is:Will increasing the angle of the ramp make my car roll further?

•What would your change variable be?•What would your responding variable be?•What would some of your control variables be?

Control variables?.

What’s wrong with this picture?

MADE OF PLASTIC

MADE OF WOOD

MADE OF PLASTIC

MADE OF PLASTIC

ANY PROBLEM HERE?

Think you have it! To use the scientific method to solve a problem, you set up an experiment to answer the question:

What is the affect of the change variable on the responding variable?

1. Change variable—the thing the experimenter changes on purpose.

3. The control variable—the other things that could cause the responding variable to change—must be kept the same.

2. Responding variable-- what the experimenter observes or measures to see if the change variable is making a difference.

Review