Food is near and dear to every one of us. We rely on it for sustenance and health, yet the understanding of food, the energy contained within it, and how it compares to our energy requirements, is likely limited. The number of Americans cooking at home increased from 2003 to 2016, especially among men1, with roughly two-thirds of all calories being store-bought and consumed at home depending on income2,3. Reported home cooking occurs at higher rates among those of low income1,3. Despite this the U.S. Bureau of Labor Statistics reported in 2015 that the average household spends $3,008 per year on eating out4. With a U.S. adult obesity rate of 42.4% in 2017-20185, whether families are eating at home or eating out, it appears that there is a lack of understanding of, or appreciation for the science of foods.
Additionally, with about 48 million cases of food poisoning each year in the United States, leading to approximately 3,000 deaths, food safety remains a concern6. Many of these cases result from undercooked meat, particularly chicken. On the other end, overcooking or irresponsible cooking behavior led to 48% of home fires and 21% of home fire deaths from 2012 to 20167. Physics is incredible in its ability to transform the way students look upon the world. Applying a little bit of physics can help us to better understand not only energy balance in our bodies, but also heat transfer in cooking. A few simple equations and experiments can help us to think more rationally and quantitatively about food and cooking. This unit aims to help students learn about the physics of food and cooking and apply the knowledge to act more responsibly and prevent some of the cases of obesity and food poisoning.
With the newly adopted Next Generation Science Standards (NGSS) in Connecticut and the focus on real-world connections and 21st century skills, the theme of cooking can be a great way to make physics engaging for students. Studying the physics concepts of energy conservation and thermodynamics can help make a seemingly abstract and quantitative subject more relatable and accessible for students. This unit has originally been designed for 11th and 12th graders in New Haven, Connecticut. Coming from a low-income community, many of the students will have an even greater reason to engage with these topics. According to Census.gov, 25.9% of New Haven residents live in poverty8. Moreover, the 2018 median household income in New Haven is approximately 65% of the national median and only 54% of the state’s median8. With higher rates of home cooking1,3 and of childhood obesity9 in low-income households, these topics are expected to be especially relevant and important for many of my students.
This curriculum unit, exploring the energy in food and the thermodynamics of cooking, will include 5 days of 80-minute lessons in which the students will pick a particular food to study. The food will either need to be purchased or produced, and will need to be a food that begins as batter or liquid and solidifies during cooking. For those students who, for any reason, cannot bring in the food, they will be provided a brownie, cupcake, or other common food item. The project will contain two main components or parts. First, the energy stored within the food will be analyzed by applying mathematics. This will require conversion between a common physics unit of kilojoules (kJ) and a common household unit of kilocalories (kcal, CAL or Calories). Students will then need to apply their knowledge of work and energy conservation to provide an example of physical exercise that would be required for them to expend an equal amount of energy that is contained in their food. If a student is uncomfortable sharing their own mass, they may use the common example of a 70-kg person. The second part of their project will involve them using experimental data to determine the heat diffusion constant for their particular food by using a method similar to that described by Rowat et al. published in 2014, “The kitchen as a physics classroom10.” This can be done by placing several thermocouples in their food sample (or probing with toothpicks as will be described later) while heating until the center of the food gets to a desired temperature. Once the diffusion constant is determined, it can then be used to derive an equation that will allow the students to determine the required cooking time based on the size of the food sample. Although larger meals may be interesting samples for the experiment, the food samples must remain reasonably small so that the experiment can be completed within a single class period and can be cooked using toaster ovens or small classroom heaters. Students, in groups of 2-3, will be required to share their data with the class so that the results can be discussed. Students will be graded on their mathematical analysis and an accurate derivation of an equation to predict cooking time based on their measured diffusion constant. Teacher checks will be structured strategically throughout the process to ensure student projects meet the requirements and that student groups remain on pace. By relating energy in food to exercises with equal outputs, and by generating equations to ensure foods will be cooked properly, students not only learn physics in an engaging way but also learn how physics can be used to tackle real-world problems.