The Scientific Method

&Experimental

Design

• The scientific method is a systematic way to help us find answers to the questions we have

• There are 5 main steps

• In science, we only deal with facts– From observations– From experiments

Step 1• Observation and

Research–See–Hear–Smell–Taste–Feel

• For example:

I got home from school and I smelled gas when I walked in my house.

Step 1, continued• Observations lead to

questions

• For example: Why does it smell like gas in my house?

Step 2

• Form a hypothesis– a statement that predicts a relationship between

cause and effect• A good hypothesis will follow the “if…then”

format• Example: If I smell gas, then there is a gas leak.

Step 2, continued

• A hypothesis must be testable.• For example: I can collect data (do a test) to

see if there is a gas leak.

• But if I said, If I wear perfume, then I will smell good

• I can’t test that

Step 3

• Gather data/experiment

• You can do this by designing an experiment, making more observations, taking measurements, etc.

Step 4• Analyze and interpret your data

• Look at the facts you collected and see if they mean anything or give you any answers.

Step 5

• Conclusion – Do you accept your hypothesis or reject it?

• If your data supports the hypothesis, you accept it

• If your data does not support it (even a tiny bit), you reject it and start over

Let’s try it

• Step 1ObservationThe light doesn’t

come on when I flip the switch.

That leads to a question: Why?

• Step 2Hypothesis

Use the “if…then” formula

If the light doesn’t come on, then

The bulb is burned outThe lamp is unpluggedThe power is out

Finish the hypothesis on your whiteboard

• Step 3ExperimentYou can check the bulb or

the plug, try other switches in the house, etc. You are gathering data to help you answer your question.

What experiment or data would you do or gather?

on your whiteboard

• Step 4Analyze Data

Look at the facts you gathered to see if they support your hypothesis or not

Let’s say your hypothesis was that the power was out and you found that none of the switches worked. That would support your hypothesis

• Step 5• Conclusion

• Accept the hypothesis

• But if you found that the other switches did work, reject the hypothesis and make a new one

Experimental Design

• When scientists design experiments, they must follow certain rules.

• A good experimental design has:– One independent variable – A dependent variable– A control group

Experiments

The independent variable is the thing you change in the experiment

ExperimentsThe dependent

variable is the thing you measure during the experiment

Experiments

• The control group is for comparison

• You do not experiment on the control group

Let’s practice – first watch me• Samantha wanted to know if fish breathe

faster in warm water. She set up three tanks:– 1 with fish in cold water (10 degrees C)– 1 with fish in room temperature water (20 degrees

C)– 1 with fish in warm water (30 degrees C)– Then she counted how many breathes they took

for 1 minute

So what is the INDEPENDENT VARIABLE? (the one thing that is different?)The temperature of the water

So what is the DEPENDENT VARIABLE? (the thing that is being measured?)

The number of breathsWhich tank is the control tank?The one with normal (room temperature) water

Let’s practice

• I want to know what kind of fertilizer will make me get the most strawberries on my plants.

• Remember: Independent Variable is what I control

• Remember: Dependent is what I am looking for

• Remember: the control group does not get the independent variable

• What will be my independent variable?

• The type of fertilizer• What will be my dependent

variable?• The number of strawberries

on each plant.• What will be my control

group?• Strawberry plants with no

fertilizer

Data

• Data collected is of 2 types:– Quantitative- numbers, measurements, etc.

• temperature, length, mass, etc.

– Qualitative – non-number data that cannot be expressed as a number• Shapes, colors, smells, etc.

Data practice...

• What kind of data would I have collected in my strawberry experiment?

• Quantitative• Why?• Because I was counting

the number of strawberries

Scientific Errors

• Poor measuring techniques• Researcher bias• Poor experimental design