# How Many Drops?

### Summary

Students will explore surface tension and the effect that tensioactive substances (soap) will have on it, through the use of coins. They will also collect data on coins and their different properties.

• Cent
• Nickel
• Quarter

• Generic

### Objectives

• Students will explore surface tension and the effect that tensioactive substances (soap) have on it, through the use of coins.
• Students will collect data on coins and their different properties.

• Science

• Math

### Class Time

Sessions: One
Session Length: 90 minutes
Total Length: 46-90 minutes

### Groupings

• Whole group
• Small groups
• Individual work

Surface tension

### Materials

For each group of 4 students:

• 3 coins:  1 penny, 1 nickel and 1 quarter
• Graphing paper
• Eye dropper
• Bottle of water
• Soap (glycerine or dish soap)
• Paper towels
1. Brainstorm with your students about their knowledge of the composition of coins.
2. Discuss the concept of surface tension as a class.
3. Distribute the materials. Ask your students to estimate and record how many drops of plain water they think will fit on each side of each of the three coins, a total of six estimates. Then have them record their estimates how many drops of soapy water each side of each coin will hold, another six estimates.
4. Have your students clean each of the coins and make sure there is no remaining soap. Explain that this type of experiment should not be done with any coins to be saved for a collection. Washing coins is not recommended for coins intended for a coin collection.
5. Have your students test their hypotheses by dropping first the plain water on each side of each coin and then the soapy water. They should record their results next to their predictions.
6. Divide the class into groups of four students. Have each group of 4 make a chart of their results. You might use stem and leaf plots of their predictions and actual results to help the students to see their data. Then have the students analyze the data for the mean, median, mode and average.
7. The students should then draw and write conclusions based on their data.

### Enrichments/Extensions

Have students add 15 drops of plain water to a penny then add 3 drops of soapy or salty water and see and report on what happens.

Use the students’ notes and graphs to assess whether they have met the lesson objectives.

### Games

This lesson plan is not associated with any Common Core Standards.

Discipline: Mathematics
Domain: All Problem Solving
Cluster: Instructional programs from kindergarten through grade 12 should enable all students to
Standards:

• Build new mathematical knowledge through problem solving
• Solve problems that arise in mathematics and in other contexts
• Apply and adapt a variety of appropriate strategies to solve problems
• Monitor and reflect on the process of mathematical problem solving

Discipline: Mathematics
Domain: 6-8 Data Analysis and Probability
Cluster: Develop and evaluate inferences and predictions that are based on data.
Standards:

In grades 6–8 all students should

• use observations about differences between two or more samples to make conjectures about the populations from which the samples were taken;
• make conjectures about possible relationships between two characteristics of a sample on the basis of scatterplots of the data and approximate lines of fit; and
• use conjectures to formulate new questions and plan new studies to answer them.

Discipline: Mathematics
Domain: 6-8 Data Analysis and Probability
Cluster: Formulate questions that can be addressed with data and collect, organize, and display relevant data to answer them.
Standards:

In grades 6–8 all students should

• formulate questions, design studies, and collect data about a characteristic shared by two populations or different characteristics within one population; and
• select, create, and use appropriate graphical representations of data, including histograms, box plots, and scatterplots.

Discipline: Mathematics
Domain: 6-8 Data Analysis and Probability
Cluster: Select and use appropriate statistical methods to analyze data.
Standards:

In grades 6–8 all students should

• find, use, and interpret measures of center and spread, including mean and interquartile range; and
• discuss and understand the correspondence between data sets and their graphical representations, especially histograms, stem-and-leaf plots, box plots, and scatterplots.

Discipline: Science
Domain: 5-8 Content Standards
Cluster: Physical Science
Standards:

• Properties and changes of properties in matter
• Motions and forces
• Transfer of energy

Discipline: Science
Domain: 5-8 Content Standards
Cluster: Science as Inquiry