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Variables in Science Experiments

Variables in Science Experiments. What makes an experiment “fair”?. Science experiments use…. Independent Variable: the one and only factor that is changed in an experiment.

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Variables in Science Experiments

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  1. Variables in Science Experiments What makes an experiment “fair”?

  2. Science experiments use… • Independent Variable: the one and only factor that is changed in an experiment. • Dependent Variable: the factor which is measured/observed in the experiment. Responds to changes in the independent variable. • Controlled variables: all the factors that stay the same in an experiment

  3. A birdy example… Imagine you want to see what color of bird feeders your local birds preferred. Red? Blue? Green?

  4. Variables • Independent Variable: color of the feeders • Dependent Variable: amount of seed eaten • Controlled: everything else that is kept the same, for example: • the location of the feeders • the kind of feeder used • putting the feeders out at the same time

  5. Our Experimental Design

  6. If everything except the independent variable is held constant, we can say: The experiment is FAIR. (ONLY the independent variable can change!)

  7. Is Sam’s experiment fair? YES? NO?

  8. Why is it important to change only 1 thing at a time?

  9. If you don’t… then you won’t know what is causing your results. Independent Variable

  10. How does diet affect a fish’s ability to swim through a maze? • Patrick thinks fish that each microwaved food are smarter than fish that do not. • Patrick times the fish going through a maze before and after eating. • 10 fish get microwaved food. • 10 fish get non-microwaved food.

  11. Variables • Independent: Microwaved food or not • Dependent: time it takes to get through the maze • Controlled: Fish species, maze, amount of food, type of food.

  12. How does a special juice affect worker productivity? • Smithers thinks that a special juice will increase the productivity of workers. He creates two groups of 50 workers each and assigns each group the same task (in this case, they're supposed to staple a set of papers). Group A is given the special juice to drink while they work. Group B is not given the special juice. After an hour, Smithers counts how many stacks of papers each group has made. Group A made 1,587 stacks, Group B made 2,113 stacks.

  13. Smither’s experiment • Independent variable: Juice or not • Dependent variable: Number of stacks of papers • Controlled variables: 50 workers were in each group. They shared the same task • Uncontrolled: The group that did not consume juice should have consumed the same amount of water.

  14. How does diet affect the length and complexity of starling bird songs?

  15. Contaminated versus Non-contminated food source. • Starlings that ate a controlled diet were compared to those that ate earthworms from a sewage treatment plant. • The starlings that ate earthworms contaminated with estrogen sang five times as long as the starlings on a controlled diet. • They also sang more complex songs.

  16. Starling experiment • Independent: Diet contaminated or not. • Dependent: Length and complexity of songs. • Controlled: Starlings • Uncontrolled: Age/gender of bird.

  17. How does brain size compare in taxi versus bus drivers? • The taxi drivers drove different routes every day. • The bus drivers drove the same route every day. • Discovery: Taxi drivers has a larger spatial memory (the part of your brain that helps you navigate) than bus drivers.

  18. Variables • Independent variable: Taxi versus Bus Driver • Dependent: Spatial memory • Controlled: Same city • Uncontrolled: Intelligence, Years of driving experience.

  19. Do marigolds planted in moon rocks grow best with or without microbes? • Two groups of marigolds were planted in crushed rock that is very similar to rocks found on the moon. • Group 1: Microbes were added to the soil. • Group 2: No microbes were added • Discovery:The marigolds with microbes added to the soil grew best!

  20. Independent: Microbes in soil or not • Dependent: Plant height • Controlled: same amount of soil and water • Uncontrolled: health of the plant

  21. What do you think? Terry loves birds and wants to see as many as she can in her yard. She wants to know whether she is wasting money buying an expensive mixed seed, when a cheaper brand just arrived at her local store. She wonders… will the expensive seed attract more birds to her back yard? How would you advise her to find out if the expensive seed is better?

  22. Terry’s Experimental Design

  23. Terry’s Experimental Design $

  24. What experiments are you planning? • What are your variables? • How will you keep your experiment fair?

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