Students will work in cooperative teams to identify and test variables that may affect the accuracy of a rain gauge. Possible variables include evaporation potential, durability of the materials, materials expansion/contraction potential, uncertainty caused by the cross-section of the opening, and location of installation. Students will share findings of their research with the class in a 'mini-meteorology-convention'.

1. Procedure:
   Divide the class into heterogenous cooperative teams of three to five students per team. Assign or have students select roles for this activity. This will help to insure a sense of positive interdependence, as well as provide some individual accountability.
• Personnel manager - Acts as the team facilitator throughout the activity. Keeps members on task, encouraging input, cooperation, and constructive feedback. Acts as liason between the team and the teacher or other groups. Participates fully with all other aspects of the project.
• Architect - In charge of the design phase of the project. Draws or oversees the drawing of the plans. Solicits input from all team members in all decisions. Insures only one variable is being tested at a time. Participates fully with all other aspects of the project.
• Engineer - In charge of the testing phase of the project. Oversees the building of the designs. Solicits input from all team members in all decisions. Participates fully with all other aspects of the project.
• Public Relations manager - In charge of the reporting phase of the project. Delegates portions of the written report to team members as appropriate, and oversees the production of the convention presentation. Solicits input from all team members in all decisions. Participates fully with all other aspects of the project.
• Laboratory Technician - In charge of all materials throughout the entire project. Oversees set up and clean up procedures daily. Participates fully with all other aspects of the project.
2. Have students work in their teams to calculate the potential error in a rain gauge caused by the 'lip' of the gauge (cross-sectional opening) using the guided worksheet "Big Lips Sink Ships".
3. Provide a variety of materials for students to use to build rain gauges.
   Suggestions:
   
   • 2 liter pop bottles
   • 5 gallon buckets
   • aluminum pie tins
   • steel cans of various sizes
   • aluminum pop cans
   • a variety of glass jars
   • paper cups
   • plastic cups
   • etc
4. Also provide materials and direction to safely cut openings into the tops of closed containers. In addition, if students want to build 'accessories' like funnels, shields, or other devices, encourage their attempts.
5. Have students select one variable that their team wants to test. Then, the team needs to design an experiment with a control setup to test their variable. (See the example format for writing up their design. This may be a useful overhead for modeling your expectations.) Each team needs to submit their written plan for approval prior to beginning their testing.
   • Possible variables include evaporation potential (determined by the size of the opening of the container), durability of the materials (paper, plastic, metal, glass), materials expansion/contraction potential (metals vs. non-metals), uncertainty caused by the cross-section of the opening (eg: Big Lips...), and location of installation (sheltered, open to wind, on ground, mounted, etc)
   • It may be difficult for students to design a perfect control for their experiment. Have them keep track of possible sources of error as they proceed.
6. Upon approval of their experimental design, students will work together to carry out their experiment.
   Tips for measurement:
   • Some experiments may require rain in order to gather the necessary data to test a variable. Known quantities of "fake rain" can be generated using a watering can with a spray spout. Use a real rain gauge to calibrate the watering can by making marks on the side of the watering can that correspond to every tenth inch of rain that is poured and collected in the real rain gauge (not all the water from the spout should fall into the gauge in order to simulate 'real rain'). Then, have students calibrate their home-made 'control' rain gauge to the watering can by reversing the process!
   • Expansion / contraction potential can be measured by making marks on a room temperature container that are known distances apart (for example, 1 mm or 5 mm). Precision in making these marks is critical. A very fine, permanent sharpie marker should be used. Then, students can heat or cool the containers, and then re-measure the distances between the lines to see if expansion or contraction occured. This might be something students want to check using a dissection scope or hand lens, if they are interested in detailed accuracy!
   • Evaporation potential should be done overnight, at least. Students will need to be very accurate in measuring equal quantities of water into their control and experimental containers. Getting ALL the water back out of the containers to re-measure the volume will be the tricky part!
   • Durability of materials will be somewhat subjective. The 'exposure to the elements' that students design should be repeatable in both style and force; so 'having Joe stomp on it' may not be a repeatable technique, but filling the container with water and putting it in the freezer overnight' would be repeatable.
   • Location of installation is best tested by making identical gauges and actually placing them outside in different locations, and then hoping it actually rains to be able to compare the results. If this is not practical, field tests that may give some data could be attempted. Setting up a fan to simulate wind, or spraying a hose to simulate driving rain or light sprinkling of rain are some ideas that students could start with.
7. Have students try their experiment several times, keeping good data each time. They should be looking for differences between their control setup and their experimental setup to see if the variable they selected will affect the accuracy of the rain gauge.
8. Give students time to prepare a short presentation describing their experiment and their results and conclusions. Encourage the use of technology in preparing their presentations. PowerPoint and HyperStudio are useful applications for presentations. ClarisWorks and Excel are valuable tools for data analysis. Computer graphics, digital cameras, clip art, and paint/draw programs can be used to create visual aids.
9. Set up the room so it feels like students are attending a 'mini-meteorology-convention'. Allow each team about 5 minutes to present their experiment, results, and conclusions to the class. Encourage audience questions and 'professional scrutiny' of each experiment. Have each person take some notes on the different variables that were tested. They will use this data to help them design an effective rain gauge for long-term use in the next activity.

• Have students rank order the variables that the class tested from "greatest potential to generate error" to "least potential to generate error" in data collection. Have students design a home-made rain gauge and justify why they selected each component.

Extension:

• Have students test several 'real' rain gauges that are on the market for the same potential sources of error as their 'home-made' gauges.