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EXPERIMENTAL DESIGN

Science answers questions with experiments

Begin by asking a question about your topic

DEFINE THE PROBLEM

What is a good question for an experiment?

One that is testable with the materials at hand

Now we need a hypothesis to guide our investigation.

What is a hypothesis?

No, It is NOT an educated guess!

Your best thinking about how the change you make might affect another factor. Tentative or trial solution to the question.An if ………… then ………… statement.

Variables are things that change.

The independent variable is the variable that is purposely changed. It is the manipulated variable.

The dependent variable changes in response to the independent variable. It is the responding variable.

Be sure to operationally defineeach variable.

What are constants in an experiment?

Factors that are kept the same and not allowed to change

What is a control?

The part of the experiment that serves as the standard of comparison.

Why is a control necessary?

It is the unchanged part of the experiment that detects the effects of hidden variables.

- Materials and Procedures
- A description of what you will use for your experiment, and how you will do it.
- Be sure to include:
- Levels of the Independent Variable
- Repeated Trials
- Drawing of Apparatus

Levels of the Independent Variable

How many different levels of the independent variable should we test?

3 ? 5? 10? The more the better?

Repeated Trials

What are repeated trials?

The number of times that a level of the independent variable is tested.

Why are repeated trials necessary?

They reduce the possibility of chance errors affecting the results.

Include Labels to clearly identify the important parts of the experimental setup

Qualitative Observations and Results

What are qualitative observations?

They are what you perceive that occurred during the course of your experiment. They are identification of trends in the data.

Quantitative Observations and Results

What are quantitative observations?

Numbers in the form of raw data displayed in data tables and graphs

Sample Data Table

Title: The Effect of the independent variable on the dependent variable

What’s wrong with this table?

Number scoops of calcium chloride

Temp. Change of water (oC) Trials

Average temp. change (oC)

1 2 3

0

0 1 0

0

2

3 5 4

4

4

6 8 7

7

6

11 11 8

10

8

10

14 15 14

17 18 16

14

17

What’s wrong with this table?

Number scoops of calcium chloride

Temp. Change of water Trials

Average temp. change

1 2 3

0

0 1 0

0

2

3 5 4

4

4

6 8 7

7

6

11 11 8

10

8

10

14 15 14

17 18 16

14

17

The Effect of Various Amounts of Calcium Chloride on the Temperature of Water

What’s wrong with this table?

Number scoops of calcium chloride

Trials

Average temp. change (oC)

1 2 3

0

0 1 0

0

2

3 5 4

4

4

6 8 7

7

6

11 11 8

10

8

10

14 15 14

17 18 16

14

17

The Effect of Various Amounts of Calcium Chloride on the Temperature of Water

What is the purpose of a graph?

Graphs communicate in pictorial form the data collected in an experiment

Graphs

Title: The Effect of the independent variable on the dependent variable

Independent Variable – include units and an appropriate scale

Bar vs. Line Graphs - Which Should I Use?

The type of graph to use depends on the type of data collected.

Two kinds of data: Discrete and Continuous

Discrete data are categorical like days of the week, color, and brand of battery. Intervals between the data have no meaning.

USE A BAR GRAPH

Continuous data are associated with measurements

involving a standard scale. Measurements should be able to show a trend or relationship. Intervals between data have meaning.

USE A LINE GRAPH

Constructing a Graph DRAW AND LABEL AXES

Temp. of Water (oC)

Y Axis - Dependent Variable

Amount of Calcium Chloride (scoops)

X Axis - Independent Variable

Constructing a Line Graph - DETERMINE SCALES

FOR AXES

Increase values on axes by 1, 2 ,5, 10 or

multiples of 10. There should be about

5 numbered subdivisions on each axis.

20

15

X: Largest value – Smallest value = Range

10 scoops - 0 scoops = 10 scoops

10 scoops divided by 5 = 2 scoops

10

Average Temp. change (o C)

Y: Largest value – Smallest value = Range 17 oC – 0 oC = 17 oC 17o C divided by 5 = 3.4 or ~ 5 oC

5

0

0 2 4 6 8 10

Amount of calcium chloride (scoops)

Constructing a Line Graph – PLOT DATA PAIRS

.

20

Data Pairs

(0, 0)

(2, 4)

(4, 7)

(6, 10)

(8, 14)

(10, 17)

.

15

.

Average Temp. change (deg C)

10

.

.

5

.

0

0 2 4 6 8 10

Amount of calcium chloride (scoops)

Constructing a Line Graph – DRAW A

LINE-OF-BEST-FIT

.

20

.

15

.

Average Temp. change (deg C)

10

.

.

5

.

0

0 2 4 6 8 10

Amount of calcium chloride (scoops)

Constructing a Line Graph – TITLE THE GRAPH

THE EFFECT OF ADDING VARIOUS AMOUNTS OF CALCIUM CHLORIDE ON THE TEMPERATURE OF WATER

.

20

.

15

.

The title should state the effect of the independent variable on the dependent variable.

10

.

Average Temp. change (oC)

.

5

.

0

0 2 4 6 8 10

Amount of calcium chloride (scoops)

Q1- What is wrong with this graph?

THE EFFECT OF ADDING VARIOUS AMOUNTS OF CALCIUM CHLORIDE ON THE TEMPERATURE OF WATER

.

20

.

15

.

10

.

Average Temp. change (oC)

.

5

.

0

0 2 4 6 8 10

1

3

5

7

9

Amount of calcium chloride (scoops)

Q2 - What is wrong with this graph?

THE EFFECT OF ADDING VARIOUS AMOUNTS OF CALCIUM CHLORIDE ON THE TEMPERATURE OF WATER

.

17

.

.

14

10

.

Average Temp. change (oC)

.

7

4

.

0

0 2 4 6 8 10

Amount of calcium chloride (scoops)

Q3 - What is wrong with this graph?

THE EFFECT OF ADDING VARIOUS AMOUNTS OF CALCIUM CHLORIDE ON THE TEMPERATURE OF WATER

.

20

.

15

.

Average Temp. change

10

.

.

5

.

0

0 2 4 6 8 10

Amount of calcium chloride

Q4 - What is wrong with this graph?

.

THE EFFECT OF ADDING VARIOUS AMOUNTS OF CALCIUM CHLORIDE ON THE TEMPERATURE OF WATER

10

.

8

.

Amount of Calcium Chloride (scoops)

6

.

4

.

.

2

0

0 5 10 15 20 25

Average Temp. Change (oC)

Q5 - What is wrong with this graph?

THE EFFECT OF ADDING VARIOUS AMOUNTS OF CALCIUM CHLORIDE ON THE TEMPERATURE OF WATER

.

20

.

15

.

10

.

Average Temp. change (oC)

.

5

.

0

0 2 4 6 8 10

Amount of calcium chloride (scoops)

Q6 - What is wrong with this graph?

.

20

.

15

.

10

.

Average Temp. change (oC)

.

5

.

0

0 2 4 6 8 10

Amount of calcium chloride (scoops)

Q7 - What is wrong with this graph?

THE EFFECT OF ADDING VARIOUS AMOUNTS OF CALCIUM CHLORIDE ON THE TEMPERATURE OF WATER

40

30

.

.

20

Average Temp. change (oC)

.

.

.

10

.

0

0 10 20 30 40 50

Amount of calcium chloride (scoops)

Analysis and Interpretation of Results

This is where you describe in words what is illustrated by your data as shown in your table and graph You also describe the meaning of the results

Possible Experimental Errors

What factors in your materials or procedure might have had an impact on your results?

Conclusion

Why or why not your results supported or did not support the hypothesis.

Hypotheses are never “wrong”. They are either supported or not supported.

Include reasons for the hypothesis to be supported or unsupported.

Recommendations for Further Experimentation

What are some practical applications of your results?

What other questions that could be tested arise from your results?

Writing A Statement of the Problem for the Experiment

What should it state?

It should state:“The Effect of the Independent Variable on the Dependent Variable”.

What is a good statement of the problem for “The Helicopter?

What is the effect of wing length on time of descent?

More about our variables:

The independent variable is the variable that is purposely changed. It is the manipulated variable.

The dependent variable changes in response to the independent variable. It is the responding variable.

What is the “Helicopter” independent variable?

length of one wing as measured in centimeters

What is the dependent variable?

time of descent as measured in seconds

Title for the Helicopter Experiment

The Effect of Wing Length on the Length of Time the Helicopter Takes to Reach the Ground

Another Look at Our Hypothesis

INDEPENDENT VARIABLE

If the length of the wings are increased,

DEPENDENT VARIABLE

then time of descent will increase.

Constants in an Experiment

Factors that are kept the same and not allowed to change

What should be kept constant in the“Helicopter”?

CONSTANTS

Same structure of helicopters

Same dropping technique

Same dropping height

The Control in an Experiment

The part of the experiment that serves as the standard of comparison.

What is a good control for the “Helicopter”?

CONTROL

Beginning length of wings (5 cm)

Levels of the Independent Variable

How many different levels of the independent variable should we test?

Enough to clearly illustrate a trend in the data - 5cm, 6cm, 7cm, 8cm…..

Repeated Trials

How many repeated trials are needed in the “Helicopter”?

At least 3, then calculate an average value for each level of the independent variable

Qualitative Observations and Results

- As we dropped the helicopter, we observed that sometimes they seemed to be affected by air currents.
- It appeared that helicopters with longer wingspans took a greater time to reach the ground

Quantitative Observations

Data Table and Graph

Sample Data Table

Title: The Effect of wing length on the time of descent

Descent Time (s)

Trials

Wing Length

(cm)

Average Descent Time (s)

1 2 3

5

6

7

8

9

3 5 4 4

4 5 6 5

6 7 5 6

7 8 6 7

9 7 8 8

The Effect of Wing Length on Descent Time

.

8

.

7

.

6

Average Descent Time (sec)

.

5

.

4

5 6 7 8 9

Wing Length (cm)

The Effect of Wing Length on Descent Time

.

.

8

.

.

6

.

4

Average Descent Time (sec)

2

0

0 2 4 6 8 10

Wing Length (cm)

Analysis and Interpretation of Results

While individual trial results showed some variation; overall, as average wing length increased from 5 through 9 centimeters, average time of descent also increased from 4 through 8 seconds.

This shows a direct correlation.

Possible Experimental Errors

Although the average results supported the hypothesis, the individual trial results showed some variation. Some possible reasons for this could be due to air currents in the room or reaction time differences between the timer and the helicopter dropper.

Conclusion

The overall results supported the hypothesis.

A possible reason for this could be due to increased surface area of the wing in contact with the air - allowing for greater air support.

Recommendations for Further Experimentation/ Practical Applications

Increased time of descent due to greater wing length suggests that increased wing length could lead to greater fuel efficiency of an actual helicopter.

Other experiments investigating factors that would contribute to greater descent time might include: making modifications in the shape of the wings, changing the number of wing blades, and making folds in the wing blades

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