EXPERIMENTAL DESIGN2008-2009

STATEMENT OF PROBLEM

• Not a yes or no answered question

• Problem should be clearly testable and specific to your investigation

• Problem should identify independent and dependent variables

Examples

• How does the distance between the fulcrum and load affect the force needed to lift the load, using a 1st class lever?

• How does the height of a hill affect the gravitational potential energy that the coaster will have at the top of the hill?

• How does the type of sugar used affect the growth of yeast cells?

HYPOTHESIS

• It must make a prediction between the dependent and independent variable.

• Most often an if-then statement, but not always.

• A rationale for the hypothesis should be given

• Make sure the hypothesis is clear and reflects the Statement of Problem.

Examples

• If the fulcrum of a 1st class lever is placed closer to the load lifted, then less force will be needed to lift the load. This is because work equals force X distance and both can change but not together. Since a machine is designed to help make work easier, by increasing the effort distance you will decrease the force needed to lift a load.

VARIABLES

VARIABLESINDEPENDENT VARIABLE

• This the factor manipulated, and it should be operationally defined, including units.

• It is suggested to have at least three levels.

• Should stem from problem and hypothesis.

Independent Variable Example

• The distance the fulcrum is from the load to be lifted as measured in centimeters.

Levels of Independent Variable: 4 cm, 8 cm,12 cm and 15 cm.

DEPENDENT VARIABLE

• The variable that responds to the Independent Variable.

• This is the data you are collecting, and for this event, it is best that it is Quantitative.

• Example: The force needed to lifted the load as measured in newtons.

Constants /Controlled Variables

• Factors that remain the same throughout the experiment so you know that it is the independent variable making the difference. Suggested to have 4 constants listed

• Examples: 1. The load lifted 2. the fulcrum used 3. Instrument used to measure force 4. Method of measuring distance.

Experimental ControlStandard of Comparison

• This is the standard of comparing the observed experimental effects.

• It can be the one not receiving the treatment of the independent variable, but it also can be one of the levels of your independent variable. Sometimes it is not appropriate to have a control group

Standard of Comparison Example

• The standard of Comparison in this experiment is when the fulcrum is exactly in the middle and the effort distance is equal to the load distance. This is the 15cm level of the independent variable.

Materials

• List the exact materials used, no extras.• List them separate from your procedure.• Include brand or model numbers if appropriate.

Be specific.• Example:

1. a 30cm plastic ruler to use as the lever. 2. a 50g weight to be used as the load3. a 3cm wood dowel to be used as the fulcrum 4. a blue spring scale to measure force

PROCEDURE

• Number and put in proper sequence.

• Give enough information so that someone could duplicate your experiment

• Use diagrams when needed to make it clear

• Make sure that you have repeated trials.

Procedure: Example

1. Gather materials listed.2. Make the lever with fulcrum at the 15 cm and load as

shown in Figure A.3. Attached the spring scale at one end of the lever and

lift the load to where it is one cm off the table.4. Record the force used to lift the load. Repeat this two

more times for accurate measurements.5. Record data in Data Table6. Repeat steps 3-5 for the other three levels.7. See Diagrams B, C and D.

Diagram A

• Diagram A

15 cm

15 cm

• Diagram B Diagram C

• Diagram D

4cm

8 cm

12 cm

QUALITATIVE OBSERVATIONS

• What are observations observed that might affect the results? Irregularities?

• Observations throughout the course of the experiment.

• Observations that may not have a direct relationship with data. These are extra observations.

• Qualitative summary of data/results given

Qualitative Observations: Examples

• When the ruler was used as a lever, it sometimes bent more than others, possibly giving different force readings.

• The force did not always stay in center when lifting, possibly giving different force readings.

• It was difficult to hold the lever at exactly 2 cm off the table, and the force readings were often difficult to read.

• Over all, the differences at each level were very small, making the average fairly accurate.

DATA TABLE

• Includes all data for each trial at each level

• Includes calculated values: Averages, maybe velocity, whatever is appropriate to experiment. Give Example Calculations.

• Division C must use significant figures.

• Data Table must have Title and Units must be displayed.

The Effect of the load distance on the effort used to lift the load.

Load Distance (cm) Force to lift load (N) Avg.(N)

Trial 1 Trial 2 Trial 3

4 cm .15 .14 .15 0.146

8 cm .19 .19 .18 0.186

12 cm .21 .22 .23 0.22

15 cm .25 .26 .28 0.26

Example Mean Calculation: Trial 1+ Trial 2+ Trial 3/ 3

GRAPH

• Graph independent variable on the X axis and dependent variable on the y axis.

• Have title and units labeled properly• Use line graph if data could take on any value

within the range on your graph• Bar Graph is most appropriate with discrete

data, data that has only specific values. ( Example how many children like snickers over

milky way)• Trends in data are represented.

Statistics

• Measure of central tendency: Mean, medium, mode

• Measure of Variation: This can be expressed by using range and standard Deviation

• Regression analysis, when data fits into an obvious trend, find the best fit line. This can be graphic or calculated.

Find Standard Deviation

1. Find the mean of the scores

2.Subtract the mean from each individual

score

3.Square each of the differences obtained

in step 2

4.Add all the squares obtained in step 3

5.Divide the total from step 4 by the total number of values minus 1 (n-1)

6.Take the square root of step 5

Find a linear best-fit line

1. Graph the data

2. Draw in an appropriate best-fit line

3. Take two points, one at beginning and one at the end of this line

4. Find the slope m=(y1-y2)/(x1-x2)

5. Find the y-intercept y=mx+b

6. Put it together in an equation

* Values nearest 1 indicate a good linear relationship.

How the Load Distance Affects the force to lift the load

0

.15

.18

2.1

2.4

2.7

3.0

Distance from Fulcrum to Load

Force (N)

Trend: As load distance increases, the force needed to lift the load decreases.

Analysis of Results

• All data is discussed and all statements must be supported by data.

• Discuss unusual data and explain why the unusual data may have occurred.

• Discuss trends and what these trends may mean

• Discuss what the statistics mean.

• This should be clear and concise!

Possible Experimental Errors

• Give possible reasons for errors and be specific. Example: The forces measured were not the same for each trial, because it was difficult to hold the weight at the same distance from the table. Just don’t say “The forces varied at each level due to human error”.

• Discuss how the errors you observed affected the data collected.

CONCLUSION

• Hypothesis is restated and evaluated based on your data. You never prove anything, either your data supports or does not support your hypothesis.

RECOMMENDATIONS FOR FURTHER EXPERIMENTATION

• Give suggestions for the improvement of your specific experiment.

• Give suggestions for other ways to test your hypothesis

• Give suggestions for future experiments that would help to understand the general problem better,

• What are practical applications of your experiment?

COACHING TIPS

• Students take the first five minutes to brainstorm and come up with their problem.

• They divide the tasks: one starts writing the Experimental Design, the other two begin the experiment and start collecting data.

• There is not enough time for one person to do all the writing.

Coaching Tips, cont.

• If the outline for the experiment is on one or two pages, ask the supervisor if you can cut it up into sections.

• Make sure each section of the design is labeled with the correct designated letter of the design. Example: a: Statement of Problem

• This is not an event for those who can not write!

Coaching Tips, cont.

• Suggested each week to take a topic, brainstorm problems to be tested. Choose one experiment to conduct each week.

• Use the rubric to grade each one and then keep them all in a log book to refer back to

• Train with at least one alternate. If you have the students, it is best to work with two groups so that you have an alternate for each position.

RESOURCES

• Science Olympiad Store

• Students and Research, Cothron, Giese, and Rezba ISBN 0-8403-7766-5

• Developing Critical Thinking, Eggen and Main, ISBN 0-89455-422-0

• Hands On Physics Activities, Cunningham & Herr ISBN 0-87628-845-X