TE Activity: Wet Pennies
Contributed by: Engineering K-Ph.D. Program, Pratt School of Engineering, Duke University
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The same phenomenon that lets a water strider walk on water also allows students to place an astonishing number of drops of water on a penny. |
Summary |
Engineering Connection |
| The engineering connection in this activity is when students design experiments to test their hypothesis. Scientists practice engineering when they design new experiments to test hypothesis. |
Contents
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| Grade Level: 7 (6-9) | Group Size: 4 |
| Time Required: 20 minutes |
Activity Dependency  :How Many Drops |
Expendable Cost Per Group
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US$ 1.00 |
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| Keywords: hypothesis, variables, controls, experimental design | |
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Related Curriculum
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| subject areas | Physical Science |
| curricular units | Students As Scientists |
| lessons | How Many Drops? |
Pre-Req Knowledge (Return to Contents)
Students should be able to calculate the average of four numbers less than fifty.
Learning Objectives (Return to Contents)
- Students will be able to give an example of a hypothesis that is based on an observation of a natural phenomenon.
- Students will be able to give an example of an experiment designed to address a specific hypothesis.
Materials List (Return to Contents)
- Small beakers (50-100 ml) or plastic cups (about 4 to 8 ounces), three per team
- Disposable pipettes, one per student plus a few extras
- Pennies, one per student
- Rubbing (isopropyl) alcohol, two 16-ounce bottles
- Vegetable oil, one 32-ounce bottle
- Paper towels, several per student
- Water
Introduction/Motivation (Return to Contents)
This activity engages students' attention very quickly and thus requires little or no introduction. Simply divide the class into teams of four, provide the materials and written instructions for students, and let them proceed with the activity.
Vocabulary/Definitions (Return to Contents)
| hypothesis: | a tentative explanation for a fact or set of observations, which can be tested objectively |
Procedure (Return to Contents)
Teacher set-up
As indicated in the student directions, each team will need three containers (beakers or cups) of liquid: one containing water, one containing rubbing alcohol, and one containing vegetable oil. For each liquid, use about 2 ounces (about one-half inch of liquid height). Label the containers.
Provide students with copies of the handout, Wet Pennies. Emphasize the need to follow the directions carefully, especially in regard to the order of the liquids they test on their pennies.
Attachments (Return to Contents)
Troubleshooting Tips (Return to Contents)
- Some students may get the mistaken idea that the water-dropping activity is some sort of contest that they can win by getting the most drops, of any liquid, on the penny. Try to avoid giving students this idea, and if they come up with it on their own, explain that the point is for them to be able to fairly and accurately compare the numbers of drops of each liquid a penny can hold -- not to compare how many drops each student can get a penny to hold. To fairly and accurately compare the number of drops of each liquid a penny can hold, students need only try to use the same dropping technique (same squeezing pressure on the pipette bulb, same height it is held above the penny) for each liquid.
Investigating Questions (Return to Contents)
- How many drops of water fit on your penny? Was this number similar to the number other members of your group got? What do you think could cause differences between the numbers you got? (Students might respond that individuals have different dropping styles (speed, height they hold the pipette above the coin, etc.) and that newer pennies seem to have a more distinct rim, which could allow more water to stay on the penny. They might also speculate that differences between the pipettes could cause different sized drops to form.)
- Did you get different averages for the three liquids? If so, which liquid allowed you to put more drops on the penny?
- Are your results consistent with those of other groups? In what ways are they the same or different?
Assessment (Return to Contents)
Student assessment is not appropriate at this time; it should occur after the class has completed the entire How many Drops? lesson.
Activity Extensions (Return to Contents)
Students may want to immediately test the hypotheses they develop as part of this activity. If time allows, some of the ideas they are likely to generate can be quickly and easily tested, and it is a good idea to encourage their enthusiasm by letting them do so. See the Lesson Closure and Lesson Extension Activities sections of How Many Drops? for more information.
Other Related Information (Return to Contents)
Acknowledgement:
This activity was originally published, in slightly modified form, by Duke University's Center for Inquiry Based Learning (CIBL). Please visit the website http://www.biology.duke.edu/cibl for information about CIBL and other resources for K-12 science and math teachers.
Contributors
Mary R. Hebrank, Project Writer and Consultant, Duke UniversityCopyright
© 2004 by Engineering K-Ph.D. Program, Pratt School of Engineering, Duke Universityincluding copyrighted works from other educational institutions and/or U.S. government agencies; all rights reserved.
Supporting Program (Return to Contents)
Engineering K-Ph.D. Program, Pratt School of Engineering, Duke UniversityLast Modified: September 26, 2008