Investigative phenomenon: Windmills and hydroelectric power plants convert energy from the movement of air and water into electricity.
The city where Mrs. G’s city is located wants to switch to 100 percent clean and renewable energy. They are considering two options, a series of small hydroelectric power dams on a river coming out of the mountains and a set of windmills in the flat sections of town where it is always windy. Mrs. G divides the class into small groups and she assigns each one to either create a proposal for wind energy or a plan for hydroelectric power. Teams begin by using mathematical thinking [SEP-5] to calculate the amount of energy their proposed project would generate. The hydroelectric group assumes that the dams will harness gravitational potential energy and use the appropriate equations to evaluate the energy produced by different height dams (Energy = mass x g x height, where the water mass is determined by the average annual flow rate on the river calculated using data collected by a USGS stream gauge that is available on the internet). The wind energy group assumes that the kinetic energy of the air is harnessed and uses the appropriate equations to evaluate the energy produced by different sized windmills (Energy = ½ x mass x velocity2, where the mass is calculated using the average density of air combined with the size of the blades and the speed of the wind. Wind velocity is calculated using the average values from a nearby weather station that posts hourly data on the internet).
Investigative phenomenon: Electric generators are not 100% efficient.
Mrs. G teaches the students about the concept of efficiency when it comes to electric power generation where only a fixed proportion [CCC-3] of the energy is actually successfully converted to electricity (while a large fraction is wasted as heat).
Investigative problem: Which clean energy power source will best meet the needs of our community?
Each team obtains information [SEP-8] about the efficiency of their energy generation technology and uses it update their estimate of the electrical energy they can generate. With these basic calculations, each team must develop a specific proposal for a power plant that will provide 100 percent of the city’s energy. The wind teams must decide how many windmills, and the diameter of the blades. The hydroelectric teams must decide how many dams and their heights. Each team produces a report outlining the benefits of their plan. The class then hosts a town hall meeting where teams communicate [SEP-8] their plans and present an argument that their proposal is better than the competing plans. This argument should be supported by evidence [SEP-7] that goes beyond the simple energy calculations but also takes into account the relative benefits and impacts of each technology on natural systems (CA EP&C II; for example, dams destroy aquatic habitat, use large volumes of CO2 in their cement, and result in water lost to evaporation; wind turbines obstruct scenic views, occupy large amounts of land, and only provide intermittent energy). These competing factors enter into all real world decisions about energy generation (CA EP&C V). Students can use a spreadsheet program to try to quantify some of these effects as they compare the impact of each proposal on the local ecosystem (HS-ESS3-3).
Everyday phenomenon: Different people eat different foods each day.
Ms. M partners with the health teacher at her school to have students record everything they eat and drink for three days. Students enter their diet into an online tool (USDA “Supertracker” at https://www.supertracker.usda.gov/) that reports their intake of different nutrients and they examine their individual diets in the health class. In Ms. M’s class, they use a different online tool to calculate the total carbon emissions from the production and transport of their food (CleanMetrics “Food Carbon Emissions Calculator” at http://www.foodemissions.com/foodemissions/Calculator.aspx). Students then enter all their data into a single online spreadsheet to compare each student’s carbon footprint from food and intake of nutrients like fat, sodium, carbohydrates, and fiber (though Ms. M hides the column with student names). The class analyzes the data [SEP-4] and notice several patterns [CCC-1] such as students that eat more vegetables and less meat have lower carbon footprints. Ms. M. asks students to create an infographic illustrating the foods that are both healthy for people and healthy for the climate. They prepare a presentation communicating [SEP-8] their findings to the people that run the school lunch program and post their infographic in the cafeteria.