Identifying Variables & Designing Investigations SCIENTIFIC METHOD Identifying Variables & Designing Investigations

What is the Scientific Method? A way of knowing An organized approach to solving a problem or answering a question

Scientific Method Problem / Question Hypothesis

Hypothesis An educated guess What you think is happening Written as a statement that can be tested and disproven In many cases you are stating that there will be (or will not be) a relationship between two things. Don’t put “I think” in your hypothesis!!

Hypothesis – yes or no? Goldfish will respire more frequently in warn water than in cold water. There is life on other planets in the universe Tree snails will move farther in a wet environment than in a dry one. The younger a kitten is, the more hours it sleeps each day. Girls will score higher on a biology aptitude test than boys. I believe moths will be attracted to light at night.

Scientific Method Problem / Question Hypothesis Experiment

Experiment Tests your hypothesis. Tests to see if there is a correlation (relationship) between two things.

Experimental Design First step – Identify your variables A variable is anything that can change. There are three types of variables that we are concerned with in an experiment.

Independent Variable something that is changed by the scientist What is tested What is manipulated The “cause” in a cause & effect relationship Also called “manipulated variable”

Dependent Variable Something that might be affected by the change in the independent variable What is observed What is measured The data collected during the investigation Also called “responding variable”

Standardized Variables Variables that are not allowed to change Only one variable can change at a time in an experiment. Otherwise you won’t know which on is actually impacting your experiment. Also called “constants” or “controlled variables”

What problem do I have with this set-up? I have two fish tanks in my room. The ones in the right tank keep dying. I want to know why. What problem do I have with this set-up?

Experiment Tests your hypothesis. Tests to see if there is a correlation (relationship) between two things. Two possible results Hypothesis is disproven Hypothesis is supported

Identifying Variables:

The researchers wanted to see if spatial sense improved as children aged. Students of different ages were given the same jigsaw puzzle to put together. They were timed to see how long it took to finish the puzzle.

Identify the variables in this investigation.

What was the independent variable? Ages of the students Age is the “cause” in the cause/effect relationship. The researchers tested kids of varying ages.

What was the dependent variable? The time it to put the puzzle together The time was observed and measured by the scientist This is the “effect” of the cause/effect relationship.

What was a controlled variable? Same puzzle All of the participants were tested with the same puzzle. It would not have been a fair test if some had an easy 30 piece puzzle and some had a harder 500 piece puzzle. Same environment, same time of day, same gender distribution of test subjects, same IQ (approx) of test subjects, etc. etc.

Another example:

An investigation was done with an electromagnetic system made from a battery and wire wrapped around a nail. Different sizes of nails were used. The number of paper clips the electromagnet could pick up was measured. .

Independent variable: Sizes of nails These were changed by the scientist This is the “cause” in the cause/effect relationship.

Number of paper clips picked up by the magnet Dependent variable: Number of paper clips picked up by the magnet This is what was observed and measured by the scientist This is the “effect” of the cause/effect relationship.

Controlled variables: Voltage of the Battery Gauge (thickness) of the wire Composition of the nail Number of time the wire was wrapped around the nail None of these items were changed

Last one:

Question – does depth influence the water temperature of a pond? What are the variables?

Independent variable – depth of the water Dependent variable – temperature Controlled variables – time of day, time of year (season), same pond Ideally, all measurements would be taken within a short period of time on the same day

Designing Investigations

Hypothesis: The farther a ball drops, the higher it will bounce. Get together with someone near you. Design an investigation to test this hypothesis. Identify the variables What exactly will be changed? How will it be changed? What exactly will be measured? How will it be measured?

Hypothesis: The farther a ball drops, the higher it will bounce. Identify the variables Independent – height ball is dropped from Dependent - Height ball bounces Standardized - Composition of surface, composition of ball, force with which ball is dropped, … What exactly will be changed? How will it be changed? What exactly will be measured? How will it be measured?

Other Considerations How many times should you repeat your test? What should you do if the data is inconsistent? How accurately should you measure your data? How should you report your data?

Scientific Method Problem / Question Hypothesis Experiment Conclusion

Conclusion Your conclusion will state whether or not there is a relationship between your independent and dependent variables. Therefore, it must include your independent and dependent variables! There is a direct correlation between the height a ball is dropped from and the height it bounces from a tile floor. The higher a rubber ball is released from, the higher it will rebound. The rebound height is approximately half the height that the ball was dropped from.

Design you own experiment Question: Other than the height that a ball is dropped from, what effects the rebound height of a rubber ball?

Turn in: Hypothesis – Be sure to include both the independent and dependent variables! Independent Variable Dependent Variable Three Controlled Variables Brief description of experiment Data Table of results Graph of results Conclusion