Experimental Design

Observing and Hypothesizing

• Observation- What you see based on facts- ex: the liquid is green

• Inference– Conclusion based on observations– Ex: this liquid must be a toxic liquid

• Hypothesis– Testable explanation for a question or problem

Independent and Dependent Variables

• Independent Variables (IV): the variable that is purposely changed, the manipulated variable

• Dependent Variable (DV): the variable that responds to the IV, also called the responding variable.

Hypothesis

• IF . . . , then, . . . because……

• If (choose an IV), then (choose a DV) because (give a reason for your prediction).

• Ex: If the number of pennies increase, then the distance the cup travels will be less because the more mass the harder it is to move.

Hypothesis

• IF (independent variable), then, (dependent variable) because…...

• Ex: If the temperature of the ketchup is increased, then the travel distance will decrease because the hotter something is the less viscous it becomes.

Identifying IV and DV in a Title

• The Effect of the Different Brands of Paper Towels on the Amount of Water Absorbed.

• The Effect of the Temperature of the Liquid on the Speed of the Molecules.

• The Effect of the Amount of Vinegar a Plant Gets on the Height of the Plant.

• The Effect of the Mass of the Cup on the Distance the Cup Moves.

Identifying IV and DV in a Hypothesis

• If the brand of paper towel is Bounty, then it would absorb the most amount of water because……

• If the temperature of the liquid is the hottest, then the speed of the molecules will be the fastest because……

• If the plant gets the most amount of vinegar, then the plant will grow the least height because…..

• If the mass of the cup is the greatest, then the distance the cup travels will be the least because……

Experiment

• Procedure that tests hypothesis• Collect information under controlled conditions

Levels of IV

• Control group– The standard used for comparison

• Experimental group– The test group– All conditions constant except the one tested

Experimental Design

• What is being tested in this experiment?

• How could you improve the experimental setup?

Experimental Design Diagram

IV: (and unit) Include the control in the first box and label it as control

TITLE: The Effect of the __(IV)__ on the _(DV)_)

HYPOTHESIS: If (pick your IV), then (pick your DV) because….)

DV: (and unit)CONTROLLED VARIABLES/CONSTANTS: (list variable that stay the same to have a “fair” experiment)

Levels of IV

No. of Trials

EXPERIMENTAL DESIGN DIAGRAMS

ELEMENTS OF THE DIAGRAM

• Title

• Hypothesis

• Independent variable (IV) and control

• Levels of independent variable

• Number of repeated trials

• Dependent variable

• Constants/controlled variables

IV:       

       

DV:Control:Controlled Variables/Constants:

Title:

Hypothesis:

SCENARIO #1• Ten lima bean seeds were planted in each of 5

identical pots found around the house that contained 500 g of "Pete's Potting Soil." The pots were given the following amounts of distilled water each day for 40 days: Pot 1, 50 ml; Pot 2, 100 ml; Pot 3, 150 ml, Pot 4, 200 ml: Pot 5, 250 ml. They all received the same amount of sunlight. Because Pot 3 received the recommended amount of water, it was used as a control. The height of each plant was measured at the end of the experiment in cm.

(The activities used on this page are fromStudents and Research: Practical Strategies for Science Classroms and Competitions, 2nd ed., by Cothron, Giese and Rezba, Kendal Hunt Publishing, Iowa, 1993 )

IV:       

       

DV:Control:Controlled Variables/Constants:

Title:

Hypothesis:

SCENARIO #2• Gloria wanted to find out if the color of food

would affect whether kindergarten children would select it for lunch. She put food coloring into 4 identical bowls of mashed potatoes. The colors were red, green, yellow and blue. The 5th bowl was plain mashed potatoes. Each child chose a scoop of potatoes of the color of their choice. Gloria did this experiment using 100 students. She recorded the number of students that chose each color.

(The activities used on this page are fromStudents and Research: Practical Strategies for Science Classroms and Competitions, 2nd ed., by Cothron, Giese and Rezba, Kendal Hunt Publishing, Iowa, 1993 )

IV:       

       

DV:Control:Constants/controlled variables:

Title:

Hypothesis:

SCENARIO #3• Susie wondered if the height of a hole punched

in the side of a quart-sized milk carton would affect how far from the container water would spurt when the carton was full of the liquid. She used 4 identical cartons and punched the same size hole in each. For the 1st carton, the hole was placed at 5 cm from the bottom, the 2nd was 10 cm from the bottom, then 3rd was 15 cm and the last one was 20 cm. She filled each container with the same amount of water and removed her finger from over the hole after the container was filled. The distance the water traveled was recorded in cm.

IV:       

       

DV:Control:Controlled Variables/Constants:

Title:

Hypothesis:

SCENARIO #4 - make this better!

• Sandy heard that plants compete for space. She decided to test this idea. She bought a mixture of flower seeds and some potting soil. Into each of 5 plastic cups she put the same amount of soil. In the first cup she planted 2 seeds, in the second cup she planted 4 seeds, in the third cup she planted 8 seeds, and in the fourth cup she planted 16 seeds. In the last cup she planted 32 seeds. After 25 days, she determined which set of plants looked best.

(The activities used on this page are fromStudents and Research: Practical Strategies for Science Classroms and Competitions, 2nd ed., by Cothron, Giese and Rezba, Kendal Hunt Publishing, Iowa, 1993 )

IV:       

       

DV:Control:Controlled Variables/Constants:

Title:

Hypothesis:

SCENARIO #5- make it better!!!

• Ester became interested in insulation while her parent's new house was being built. She decided to experiment which insulation kept the temperature in the house the most stable. She filled each of 5 jars half-full with water. She sealed each jar with a plastic lid. Then she wrapped each jar with a different kind of insulation. First one had no insulation, the 2nd was wool, the 3rd was lace, the 4th was cotton and the last jar had nylon. She put the jars outside in the direct sunlight for 3 hours. Later, she measure the temperature of the water in each jar in *C.