Scientific Method and Lab Skills

What is science? The search for truth. Discovering how the world works.

An attempt to understand the world we live in.

Scientific Method

A way to solve problems

Basic Steps:1. Make observations. Ask questions2. Hypothesis3. Experiment4. Observe and gather data5. Analyze data6. Conclusion7. Peer review

Observation: Data collected with any of your senses or tools such as thermometers, balances or rulers.

Inference: Conclusions or deductions based on observations. (they may be subtle and you may be unaware you are making them)

Opinion: everyone has them, but leave them out of data collection and analysis.

Person One Person Two

Situation: A man is lying in the gutter. Situation: A man is lying in the gutter.

Inference: That man’s a bum. Inference: That man is in need of help.

Assumption: Only bums lie in gutters. Assumption: Anyone lying in the gutter is in need of help.

Honey badger

Hypothesis A hypothesis is an educated prediction

of what you think will happen in the experiment.

A hypothesis must be falsifiable. If it can not potentially be proven false, then there is nothing to test.

Example…

Why is the following example not falsifiable, therefore not testable??

Example…

``the moon is populated by little green men who can read our minds and will hide whenever anyone on Earth looks for them, and will flee into deep space whenever a spacecraft comes near''

Practice “Scott and Ian, identical twins, are sleepy

every day in their 1:00 history class: they often doze and want to know why, so they can prevent the drowsiness and improve their history grades.”

Make a list of possible hypotheses about why they are sleepy.

Possible hypotheses for twins:

1. If they get 8 hours of sleep, then they will not be sleepy in their history class.

2. If they eat a lighter lunch, then they will be less sleepy during class.

3. If they stop taking cold medication, then they will be less sleepy during class.

Experiment All experiments have two main groups:

– The Experimental Group– And the Control Group

– These two groups are exactly the same except for the one thing you are testing.

Control Group This group serves as a comparison

to the test group. This group has “normal” conditions.

– Example: Plant is given no fertilizer– Example: Patient is given a placebo/fake

medication.

Experimental Group Contains the variable you are testing

– Example: Plant WITH fertilizer– Example: Patient WITH medication

– **Make sure you are only testing ONE thing at a time.

Independent Variable The variable you are testing.

– The amount of light a plant gets– How much exercise a rat gets– The amount of vitamin C you take.

Dependent Variable What you are measuring

– The results of the independent variable

– How much carbon dioxide is excreted– The height of a plant– The weight of a rat– The sleepiness of the twins

Constants (or controls) The test group should have only ONE

variable (what you are testing).

All other variables between your groups must be the same.

Find the mistake

Draw this picture in your notes

Find the mistake

Too many Variables

-Size of cup

-Temperature of water

Find the problems

Draw this picture in your notes

Find the problems

Variables- Types of Soil

- Amount of light

-Type of Plant

Correct Set up

Characteristics of a good experiment

1. Can be repeated and get the same results 2. Have a large sample size 3. Performed for longer periods of time 4. Test only one independent variable 5. Is objective and unbiased. 6. Make accurate measurements.

Small groups vs. large groups

If you test the effects of a medication on two people instead of 100 people, why is that a problem?

Placebos A placebo is “fake medicine”, usually

a sugar pill given to the control group.

The patient thinks they are getting real medicine but are only getting a sugar pill.

The “effects” of the placebo can be compared with the effects of the real medicine.

Blind and double blind studies

an experimental procedure in which neither the subjects of the experiment nor the persons administering the experiment know the critical aspects of the experiment; "a double-blind procedure is used to guard against both experimenter bias and placebo effects"

Data Collection and presentation

In order for your experiment to remain reliable, your data must be reliable.

Make accurate measurements.

Don’t ignore data you don’t like or agree with.

Organize data into tables and graphs

A graph can make pages of raw data make more sense.

Overall patterns can be seen better with a graph.

Conclusion This is where you ask…. Did my data

support my hypothesis?

If your data supports your hypothesis, you are on your way to a theory.

If your data does not support your hypothesis, you try a different experiment.

Conclusion must be based on data.

Limitations of an experiment:

*You must be careful not to draw conclusions that are not supported by your data. In an experiment on rats, for example, conclusions cannot be automatically

applied to other animals.

Dr. Connors turns into a lizard

Peer Review Why peer review?

– People make mistakes– People lie

Experiment results are published and other scientists check their work for mistakes and can repeat the experiment to see if it really works.

Hypothesis: educated guess

Theory: Hypothesis tested true many times.

Law: Still testing true and can lead to accurate predictions.

All scientific explanations are subject to change or improve!

History of measurements Distance: In all traditional measuring systems, short distance units

are based on the dimensions of the human body. – The inch represents the width of a thumb;

in fact, in many languages, the word for "inch" is also the word for "thumb."

The f oot (12 inches) was originally the length of a human f oot, although it has evolved to be longer than most people's f eet.

The yard (3 f eet) seems to have gotten its start in England as the name of a 3-foot measuring stick, but it is also understood to be the distance f rom the tip of the nose to the end of the middle finger of the outstretched hand.

Finally, if you stretch your arms out to the sides as f ar as possible, your total "arm span," f rom one fi ngertip to the other, is a f athom (6 feet).

Metric System: Designed during the French Revolution of the

1790's, the metric system brought order out of the conflicting and confusing traditional systems of weights and measures then being used in Europe. Prior to the introduction of the metric system, it was common for units of length, land area, and weight to vary, not just from one country to another but from one region to another within the same country.

The Earth itself was selected as the measuring stick. The meter was defined to be one ten-millionth of the distance from the Equator to the North Pole. The liter was to be the volume of one cubic decimeter, and the kilogram was to be the weight of a liter of pure water.

Even more accurate…

meter (m)

distance "The metre is the length of the path travelled by light in vacuum during a time interval of 1/ 299 792 458 of a second."

kilogram (kg)

mass "The kilogram is equal to the mass of the international prototype of the kilogram."

second (s)

time "The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfi ne levels of the ground state of the caesium 133 atom."

MeasurementsMeasurement Metric

Unit

English

Unit

Tools

Length Meter Feet Ruler

Mass Gram Pound Scale

Volume Litercm3

Gallon Graduated cylinder, beaker

Temperature Celsius

Kelvin

Fahrenheit Thermometer

SI units scaleKilo- 1000

Deka- 10

(Base) 0

Deci- .1

Centi- .01

Milli- .001

Micro- .0000001

Nano- .000000001

Unit Conversion

K H D B D C M

24 meters = _______ cm

997 mm = ______ km