Data Collection Techniques

Biblical Reference

But where can wisdom be found? Where does understanding dwell?

Job 28:12

Physics Labs• The purpose of performing physics labs is

not only to reinforce the material you learned in the classroom, but also to enhance your understanding of how scientific knowledge actually progresses.

– Labs also give you hands-on experience with making measurements and interpreting data

Data Collection• Each lab will involve either quantitative or

qualitative data.• Quantitative Data Sources:

– Gauges• Micrometer, Meter Stick, Thermometer, etc.

– Sensors• Force, Motion, Light, etc.

– Meters• Voltmeter, Ammeter, etc.

• Qualitative Data Sources:– Type of Condiment, Color, Type of Mirror, etc.

Data Integrity• It is important to record accurate and

consistent data.

– However, there will be a learning curve with some of the equipment, and some of the equipment may be less precise and/or accurate than others.

– In addition, there may be some environmental sources of error.

Handling Sources of Error• Relative Discrepancy or Experimental

Error is one method to document experimental error.

– Most labs will include questions about your relative discrepancy.

– All reported results should include the experimental error.

Relative Discrepancy = |Error| x 100 Accepted Value

Example: 0.56 m ± 0.005 m

Graphing Data• During most labs, you will only change one factor at

a time. • A variable is any factor that might affect the behavior

of an experimental setup. • The independent variable is a factor that is

changed or manipulated in an experiment. (variable you control)

• The dependent variable is a factor that depends upon the independent variable.

Example – The temperature of a balloon is changed to observe the affect upon the volume.

Graphing DataLine of best fit is a better method of predicting the trend of the graph versus one point.

Is the graph missing anything?

Regression Equation

3.9734.0 TV

Direct vs. Inverse Relationships

Direct - This is where the two variables do the same thing. That is, if one increases so does the other and vice versa.

Inverse - This is where the two variables do the opposite. If one variable increases, the other variable decreases.

Correlation• Part of the data analysis process is to

create a regression equation to find a relationship between the independent and dependent variables.

• Correlation is a term used to describe how well your data fits the proposed regression equation.– Correlation (represented by the letter “r”)

varies from -1 (inverse relationship) to +1 (direct relationship).

– The closer to ±1, the better the fit.

Various Correlation Values

x

y

Strong negative correlation

x

y

Weak positive correlation

x

y

Strong positive correlation

x

y

Nonlinear Correlation

r = 0.91 r = 0.88

r = 0.42r = 0.07

Common Lab Mistakes• Mistakes are different from experimental

errors.• The following mistakes can be avoided if

care and caution are taken:– Misreading scales (using equipment incorrectly)– Arithmetic and algebraic errors– Incorrectly transferring raw data to the data

tables– Using the wrong theory and/or equations

A Few Last Words…• You will only get out of the labs what you

put into them.

• The lab equipment is sensitive and very expensive.

• Lab etiquette entails cleaning up after yourselves and returning all equipment to its correct location.

• Have fun!