How Much Water Can a Penny Hold?

Transcription

1 How Much Water Can a Penny Hold? Melinda Pittis Lexington School for the Deaf Jackson Heights, NY Summer 1999 Research Host: Thomas H. Hintze, Ph.D. New York Medical College

2 HOW MUCH WATER CAN A PENNY HOLD? Suggestions for Teachers Purpose The purpose of this activity is to perform a simple experiment to answer the question how many drops of water can you put on a penny? comparing the use of controlled and uncontrolled variables. This is a good activity for middle or younger high school students who have had limited exposure to experimental design. Additionally, students will design their own controlled experiment to answer their own research questions. Objectives Upon completion of this activity, students will be able to 1. identify independent and dependent variables 2. calculate the mean, median, range and standard error for data collected 3. demonstrate precision and accuracy in data collection 4. design and organize a data table 5. graph data using a horizontal bar graph (box plot) 6. compare graphs for controlled and uncontrolled experiments 7. properly state and answer a hypothesis Materials Each student will need the following: Dropper Penny Sheet of graph paper/pencil Small cup of water Preparation and Procedure This is a good lab to perform in the beginning of the year, when students are learning principles of experimental design. There are no special preparations that need to be done in advance, and no prior knowledge is necessary for this experiment. Part 1: The Controlled vs. Uncontrolled Experiment The purpose of part 1 is to compare the results between an uncontrolled experiment and a controlled experiment. For Trial 1, students are asked the simple question "How many drops of water can a penny hold?" They are given no direction or instruction, but allowed to proceed with whatever methods they want. After each individual or group has gotten a number, results should be recorded on the student data sheet. Together, the methods detailing how each

3 group dropped water on the penny should be listed and recorded on the data sheet. Methods will vary greatly and should include things such as how the dropper was held (straight or angled), how high the dropper was held above the penny, the shape of the dropper, if the heads or tail side was used, if the penny was shiny or dull, clean or dirty, old or new, and if water was dropped repeatedly in the same location or in different places on the penny. When the list is generated, students should calculate the mean, median, range and standard error and record them. Prior to beginning Trial 2, students should discuss and agree upon how they will conduct the second trial. Everyone must demonstrate similar methods. Again, record everyone's numbers and calculate the statistics. The range and standard error should decrease significantly, although the mean usually increases. Continue on to the conclusion questions, where students can easily construct a box plot to show the range. It is also helpful to include a vertical line to represent the mean for each trial. The box plot provides a clear, visual means to compare experiments with uncontrolled and controlled variables. It is important to emphasize how different groups results from the uncontrolled experiment cannot be compared. The box plot clearly shows how the range is reduced when variables are controlled. Part 2: Student-Designed Research Questions Part 2 will allow students to create their own research questions related to how many drops of water the penny will hold. Students often already have questions ready from part 1, such as wondering if the penny will hold more on the heads or tails side, or if a dirty penny can hold more water than a clean one. Students should develop a question and hypothesis and follow the same procedures agreed upon in part 1 for consistency. Make sure to check each group's problem and hypothesis before they begin work. Additionally, they will need a system to collect and show data. Each group should create an appropriate chart for data collection and develop a graph to show the results to the class. Ideas for data collection and graph can be drafted on the Student Data Sheets for Part 2. Safety There are no special safety issues for this activity. Students should follow whatever rules have been established for regular laboratory experiments.

4 Questions to Ask 1. What is meant by a "control?" 2. Compare your results from part 1 for the controlled and uncontrolled trials. Why is the range different? Can you think of any way to reduce the range further? 3. For part 2, identify your independent and dependent variables. 4. Provide definitions, formulas and practice for calculating the mean, median and standard error. Where to Go From Here The approach of this lab can be applied to most future labs, which will always have questions related to controlling variables. You can always to back to the penny lab and comment "remember the pennies!" Even something as simple as watching how students perform traditional "cookbook labs" can provide opportunities for limiting variables. Making note of different techniques students use during any lab can provide great questions to ask about variables and how they affect results. References and Resources This project is adapted from a lab originally written by: SEAQL - Science Education and Quantitative Literacy Suggestions for Assessment 1. Students will need to share their own research questions and conclusions with the members of the class. This can be done with either posters or presentations. Students should be allowed to make suggestions for each others' experimental designs. 2. Situations of poor lab design can be given as part of a test or quiz, where students must improve or redesign the experiment. 3. Students can be given a simple research question and asked to discuss the experimental design. This can also be part of a test. 4. Many schools do annual science fairs. A science fair is an optimal time to test or allow for more practice time with experimental design, where students conduct their own original research to answer student-generated questions.

5 HOW MUCH WATER CAN A PENNY HOLD? A Lab for Experimental Design There is a simple question for this experiment: How many drops of water can you put on a penny? The purpose of this lab activity is to learn some useful strategies for lab that you will use throughout the year. Objectives Determine how many drops of water will stay on a penny Determine a more accurate approach to the same experiment demonstrating better techniques Calculate the mean, median, range and standard error for data collected Demonstrate precision and accuracy in data collection Graph data using a horizontal bar graph Compare graphs for controlled and uncontrolled experiments Materials Penny Dropper Small Cup of Water Procedures for Trial 1 Your goal is to try to fit as many drops of water on a penny as possible. Use any method you wish. Use the next page to record your numbers. Remember and write down on the data sheet any technique or method your group used. Record all of the class data: each individual or group should report their number of drops. Calculate the average (mean), median, range and standard error for the class numbers. Procedures for Trial 2 Discuss with the class the methods you will use for the second trial. Write down the procedures you agree to follow. The method you choose does not matter, but it is important that you all do the same thing. Record each group's number of drops again on the data sheet and again figure out the average, median, range and standard error. Now make a horizontal bar graph (box plot) on the handout provided (together with whole class). The box plot is just a box that represents the whole range. Add a vertical line to indicate the mean for each trial.

6 PART 1 STUDENT DATA SHEET TRIAL 1 (UNCONTROLLED) TRIAL 2 (CONTROLLED) Number of drops: Number of drops: Methods used: Methods used: Class Mean: Class Median: Class Mean: Class Median: Class Range: Class Range: Standard Error: Standard Error:

7 Conclusions 1. Make a horizontal box plot (as a class) comparing the "controlled" and "uncontrolled" results. The horizontal bar will reflect the range. Mark the average and median on each line. You will have to mark the horizontal scale using the range for class data. Controlled Uncontrolled 2. Why is it important that everyone uses the same method for data collection? 3. Compare the ranges for the controlled and uncontrolled experiments. What can you conclude? What can you conclude about the standard error? 4. What did you learn in this lab that will apply in future labs?

8 PART 2 STUDENT DATA SHEET Members of your group: Your research question: Your group's hypothesis: Materials: Procedures: Make a concise list of how you will conduct your experiment. It should be clear enough so that another person unfamiliar with the lab can reproduce your experiment.

9 Results: Design a chart (before you start your experiment) to collect data in an organized way: How will you show your results? (Design an appropriate graph with independent and dependent variables labeled). Conclusions: Answer your original question, and address your hypothesis: Be prepared to discuss the results of your experiment to the class. Prepare your summary on poster board or chart paper, including the research question, hypothesis, procedures, data/results (on graph paper), conclusion and sources of error/improvements.