Designing an Experiment I. Determining a Purpose An experiment is an organized procedure to study something under controlled conditions. Write the purpose of your experiment as a question or problem you want to investigate

Investigating a Problem To design an experiment, you need a purpose for the experiment. The purpose is the question you wish to investigate. The question should be written so that it cannot be answered with a “yes” or a “no”. Observation: You notice that the rocks in the middle of the river have rounded edges. On the edge of the river, the rocks have sharper edges. Question: Why are the rocks in the middle of the river more rounded than those on the edges?

Observation: You put a plant on a windowsill. After a few weeks, you notice that the leaves have all turned toward the window. Question: Why do the leaves of a plant turn toward the window? Observation: You notice that when you eat chocolate ice cream at night, you have trouble falling asleep. Question: Is there something in chocolate ice cream that keeps me awake at night?

Does increasing the air in a basketball make it bounce higher? You observe when playing basketball that sometimes the ball bounces higher. Later, while filling the basketballs with air you notice that the amount of air in the basketballs can be different. Question: Does increasing the air in a basketball make it bounce higher? Prediction: Increasing the air in a basketball will/will not make it bounce higher. Observation #1

Cars on higher ramps will/will not travel farther. While watching your brother play with his toy cars, you notice when he rolls them down a ramp that they travel different distances. You wonder if the height of the ramp has any affect on how far the cars travel. Question: Will increasing the height of a ramp cause a car to travel farther? Prediction: Cars on higher ramps will/will not travel farther. Observation #2 5

Will soaking seeds in water affect sprouting time? Prediction: Question: Will soaking seeds in water affect sprouting time? Prediction: Seeds soaked in water will sprout faster. Question: 2. Will freezing popcorn affect the amount of kernels that pop? Prediction: Freezing popcorn will cause more kernels to pop. Question: 3. Will increasing the temperature of water affect the amount of time it takes sugar to dissolve? Prediction: Increasing the temperature of water will cause sugar to dissolve faster. Packet p.3

4. Does the temperature at which bread is stored affect mold growth? Question: 4. Does the temperature at which bread is stored affect mold growth? Prediction: Storing bread at cooler temperatures will cause mold to grow more slowly. Question: 5. Does water temperature affect the time it takes water to freeze? Prediction: Increasing water temperature will cause water to freeze more quickly. Packet p.3

II. Writing a Hypothesis A hypothesis is a tentative explanation for an observation or scientific problem that can be tested by further investigation. A hypothesis is written in the form of an if/then statement.

You observe when playing basketball that sometimes the ball bounces higher. Later, while filling the basketballs with air you notice that the amount of air in the basketballs can be different. Question: Does increasing the air in a basketball make it bounce higher? Prediction: Increasing the air in a basketball will/will not make it bounce higher. Hypothesis: If the amount of air in a basketball is increased, then it will bounce higher. Observation #1 p. 4 9

Cars on higher ramps will/will not travel farther. While watching your brother play with his toy cars, you notice when he rolls them down a ramp that they travel different distances. You wonder if the height of the ramp has any affect on how far the cars travel. Question: Will increasing the height of a ramp cause a car to travel farther? Prediction: Cars on higher ramps will/will not travel farther. Hypothesis: If the height of a ramp is increased, then a car will travel farther. Observation #2 p. 4 10

Will soaking seeds in water affect sprouting time? Hypothesis: If seeds are soaked in water, then seeds will sprout faster. 2. Will freezing popcorn affect the amount of kernels that pop? Hypothesis: If popcorn is frozen, then more kernels will pop. 3. Will increasing the temperature of water affect the amount of time it takes sugar to dissolve? Hypothesis: If the temperature of water is increased, then sugar will dissolve more quickly. Packet p.5

4. Does the temperature at which bread is stored affect mold growth? Hypothesis: If bread is stored at a cooler temperature, then mold will grow more slowly. 5. Does water temperature affect the time it takes water to freeze? Hypothesis: If water temperature is decreased, then water will freeze more quickly. Packet p.5

III. Determining Variables and Constants a. Variables and Constants i. A variable is any factor in an experiment that can change. ii. Constants are all of the factors that are the same. iii. The independent variable is the factor you want to test. An independent variable is expressed in your hypothesis after the word “If”. v. The dependent variable is the factor that you measure to get your results. A dependent variable is expressed in your hypothesis after the word “then”.

Hypothesis #1 : If the amount of air in a basketball is increased, then it will bounce higher. Independent variable: amount of air Dependent variable: height of bounce Hypothesis #2: If the height of a ramp is increased, then a car will travel farther. Independent variable: ramp height Dependent variable: distance traveled

percent of kernels popped If seeds are soaked in water, then seeds will sprout faster. Independent variable: Dependent variable: 2. If popcorn is frozen, then more kernels will pop. 3. If the temperature of water is increased, then sugar will dissolve more quickly. soaking seeds sprouting time freezing popcorn percent of kernels popped water temperature dissolving time

time it takes mold to grow 4. If bread is stored at a cooler temperature, then mold will grow more slowly. Independent variable: Dependent variable: 5. If water temperature is decreased, then the water will freeze more quickly. storing temperature time it takes mold to grow water temperature freezing time

b. Measuring the Dependent Variable i. An operational definition is a description of the particular way in which you will measure the dependent variable. ii. Operational definitions can be qualitative or quantitative.

Defining Variables Operationally Hypothesis: If students have more lunch money, then they will eat a poorer quality diet. Hypothesis: If students spend more time studying each week, then they will do better in school. Hypothesis: If fertilizer is added to tomato plants, then they will grow better.

Identifying Variables 1. What variables can affect the rate at which seeds sprout? soaking seeds temperature sunlight type of seed soil What variables can affect the number of popcorn kernels that pop? freezing type of popcorn popping time microwave popcorn brand

3. What variables can affect the dissolving rate of sugar in water? water temperature type of sugar amount of sugar amount of water stirring 4. What variables can affect mold growth on bread? storing temperature type of bread storage container amount of sunlight/darkness moisture in bread

5. What variables can affect the time it takes water to freeze? water temperature container amount of water freezer location and temperature in freezer 21

Controlling Variables Hypothesis #1 : If the amount of air in a basketball is increased, then it will bounce higher. Independent variable: Dependent variable: amount of air height of bounce The constants are all the factors that are the same. same basketball same temperature same surface same bounce height Packet page 8

Independent variable: Hypothesis #2: If the height of a ramp is increased, then a car will travel farther. Independent variable: Dependent variable: ramp height distance traveled Constants: same surface same car same ramp

Example #1 Hypothesis: If seeds are soaked in water, then they will sprout faster. Independent variable: soaked seeds Dependent variable: sprouting time Constants:

Example #2 Hypothesis: If popcorn is frozen, then more kernels will pop. Independent variable: freezing kernels Dependent variable: percentage of popped kernels Constants

Independent variable: Example #3 Hypothesis: If the temperature of water is increased, then sugar will dissolve more quickly. Independent variable: water temperature Dependent variable: dissolving time Constants

Independent variable: Example #4 Hypothesis: If bread is stored at a cooler temperature, then mold will grow more slowly. Independent variable: storing temperature Dependent variable: mold growth Constants

Example #5 Hypothesis: If water is decreased then freezing time will decrease. Independent variable: water temperature Dependent variable: time it takes to freeze Constants 28

Independent variable: Experiment #1 Mr. Hunsicker has observed that the batteries in his boom box seem to last longer if he plays his boom box at low volume rather than high volume. He wants to design an experiment to determine if this is true. If a boom box is played at low volume, then the batteries will last longer. Independent variable: boom box volume Dependent variable: battery life Constants: boom box batteries CD

number of daylight hours henhouse-climate/temperature Experiment #2 An investigator has observed that chickens lay more eggs at certain times of the year. It has also been observed that this occurs during the late spring and summer months. An inference has been made that the extra eggs are due to the longer daylight hours. If the number of daylight hours is greater, then chickens will lay more eggs. Independent variable: number of daylight hours Dependent variable: number of eggs laid Constants: chickens henhouse-climate/temperature diet/water

type of street traveled gas mileage car driver type of gas Experiment #3 Johnny made an observation that when he drove around the city on the highway to work everyday, he did not have to get gas as often as when he drove through the city. He then asked himself Do the type of roads I drive to work on everyday affect my gas mileage? If cars are driven on the highway, then gas mileage will increase. Independent variable: type of street traveled Dependent variable: gas mileage Constants: car driver type of gas

If bread is moist, then mold will grow faster. Experiment #4 Troy wanted to determine if mold grows faster on moist bread or dry bread. He placed one piece of bread in a dry baggie and another piece of bread in a damp baggie. He checked them every eight hours and recorded his observations. If bread is moist, then mold will grow faster. Independent variable: moisture on bread Dependent variable: mold growth Constants: bread temperature sunlight

different types of drinks Experiment #5 Hannah wanted to test the ability of different drinks to dissolve bones. She filled glass jars with orange juice, milk, cola, and distilled water. Hannah then placed a chicken bone in each of the jars. Independent variable: different types of drinks Dependent variable: dissolving of bone Constants: bones – size and type amount of liquid temperature

percent of kernels popped Experiment #6 Sarah wanted to determine which of three brands of popcorn popped the most kernels. She put one brand in the microwave, set the timer for four minutes, and allowed the bag to pop. She repeated this process for each bag. Independent variable: brand of popcorn Dependent variable: percent of kernels popped Constants: microwave time type of popcorn

Summarizing Results When summarizing your data, look at all of your observations, Then look for meaningful ways to present your observations.

Data Tables Growth Rate of a Child Age (years) Weight (kg)

Graphs Line graphs are useful for showing changes over time. The dependent variable is placed along the y-axis. The independent variable is placed along the x-axis.

Bar graphs are useful for comparing data. The dependent variable is placed along the y-axis. The independent variable is placed along the x-axis.

Birth 1 year 2 years 3 years 4 years 5 years Growth Rate of a Child . 20 18 16 14 12 10 8 6 4 2 . . . Weight (kg) . . Birth 1 year 2 years 3 years 4 years 5 years Age (years)