Scientific Method: Designing an Experiment

Identify the following as qualitative data and quantitative data:1. Making a mango shake requires 5L of milk.2. The average population of a city is 90%.3. Jim is a tall boy.4. The majority of the people in India wear the color red most often.5. The sidewalk is long.6. The sidewalk is 100m long.7. The race was over quickly.8. It is warm outside.9. They drank 4 cups of tea.

A. Variables

1. Variables: The conditions that can change during an experiment 2. There are always at least two variables of interest in an experiment a. Example Question = Does working out help a person to lose weight? b. What are the two variables in this experiment that we want to investigate?

What is a variable?

• Pea plant clones given different amounts of water for a three-week period. In addition to receiving water through natural ways- First pea plant receives 400ml extra, the second plant receives 200ml extra, the third plant receives 100ml extra. The fourth pea plant does not receive any extra water; it only receives water through natural ways. The height of the pea plants are recorded daily.

3. Types of Variablesa. Independent Variable = the variable that you change ~ you have direct control. • Example = Amount of workout b. Dependent Variable = the variable that changes as a result of the independent variable. The variable that you do not have control over. • Example = loss in weight

c. Controlled variables = variables that should remain constant and should not change during the experiment. • Type of workout• Duration of workout • Diet of the person• Time of the workout

B. Controlled Experiments

1. An experiment that tests the effects of one independent variable at a time. Researcher attempts to keep all other variables constant 2. Test subjects are divided into a control group and an experimental group

a. Control Group - independent variable is not changed to provide a comparison. Conditions are set to “normal” • Example:b. Experimental Group - independent variable is changed and the results are compared to the control group • Example:

C. Sources of Error

1.Things that can change the result of the experiment a. Variation in test subjects b. Human error c. Poor experimental design d. Problems with instruments

Designing an Experiment- Practice

• FISH EGGS: A scientist knows that the percent of fish eggs that hatch is affected by the temperature of the water in an aquarium. She is attempting to identify which water temperature will cause the highest percentage of fish eggs to hatch. The scientist sets up 5 aquariums at the following temperatures: 10°C, 20°C, 30°C, 40°C, and 50°C. She adds 50 fish eggs to each aquarium and records the number of eggs that hatch in each aquarium.

FIRE EXTINGUISHERS: A firefighter is trying to figure out which type of fire extinguisher (CO2, water, or dry chemical) will put out fires the fastest. Think about the issue being tested and imagine an appropriate experiment to determine which type of fire extinguisher can extinguish fires the fastest.

MOUTHWASH: The makers of brand A mouthwash want to prove that their mouthwash kills more bacteria than theother 4 leading brands of mouthwash.They organize 60 test subjects into 6 groups of 10 test subjects. The data for the experiment is shown to the right.

mouthwashused

time mouthwashwas in mouth

# of bacteria inmouth (average)

none 135

A 60 sec. 23

B 60 sec. 170

C 60 sec. 84

D 60 sec. 39

E 60 sec. 81

GAS MILEAGE: A car magazine is trying to write an article that rates the top 5 most fuel efficient SUVs (the SUVs that can drive the most miles for each gallon of gasoline). They make sure each model of SUV has exactly 10 gallons of gasoline in its fuel tank and reset the odometer (instrument that measures the distance a vehicle has traveled) to zero. The SUVs are then driven until they run out of gasoline. The distance on the odometer is recorded.