- Independent Variable: Every experiment should only have one independent variable. If there is more than one independent variable (part changed by the scientist), then it will be impossible to determine what effects were caused by a particular change.
- Multiple Trials: Repeating a science experiment is an important step to verify that your results are fair and not just an accident. For a typical controlled experiment, you should have at least 3 repeated trials (more is better).
- Human Error: Experimental error is always possible as human beings. Any time we make a qualitative or quantitative observation, there is a degree of uncertainty. This may be due to pre-existing limitations in the measuring equipment (ex: broken thermometer), or of the measuring techniques, or perhaps the experience and skill of the experimenter.
- Constants: Every experiment should have as many constants as possible. Constants are parts of the experiment that a scientist keeps the same to insure that the only part of the experiment affecting the results is the independent variable (the part changed by the scientist).
Identify one type of limitation in each experiment (questions 1-3) that you think will most affect the reliability of the data. Make sure to explain why you chose the particular limitation. YOU DO NOT NEED TO WRITE THE QUESTIONS.
1. Ashik filled 3 pots with EcoScraps soil and labeled them A, B, and C. He then placed 1 radish seed in the middle of each pot. Ted added 1 teaspoon of fertilizer to pot A, put 2 teaspoons in pot B, and no fertilizer in pot C. After using a different amount of fertilizer in each pot, he placed pot A on a sunny windowsill, pot B on a shady windowsill, and pot C in a dark closet. Ashik watered each plant with a ½ a cup of water every day. As he measured each plant throughout the month, Ashik wrote the height of the plant (in centimeters) in his data table for trial one. Ashik repeated the same experiment for trial 2 and trial 3. Identify one limitation in Ashik's experiment.
2. Paula wanted to find out if the type of soda (diet coke vs. regular coke) affected the time it takes to "go flat" (lose carbonation). She figured the best way to determine when the soda went flat was by tasting the sodas every 30 minutes. For each trial, Paula set a timer for 30 minutes, then tasted the diet coke first, immediately followed by the regular coke. She recorded whether or not the soda was flat after each taste test. She performed a total of 5 trials. Identify one limitation in Paula's experiment.
3. Rashonne wanted to find out what color Crayola marker (red, yellow, green, orange, blue, purple) dries out the fastest. She purchased one box of markers and set out all 6 colors on a flat surface in the same location with the same temperature, where each marker received an equal amount of sunlight. She removed the caps and checked them twice a day to record the time for each marker to dry. Identify one limitation in Rashonne's experiment.
4. True or False: "If a procedure is very well planned out, then there will be no mistakes in the data." Explain your choice.