Explanation

The goal of science is to explain the natural world.  As such, explanation should be our goal in science education as well. In this section, we provide resources for helping students build explanations of anchoring phenomena throughout an MBI unit.

Below is an example evidence-based explanation from the example Baking Cookies unit designed for a middle school physical science class. The driving question the students were answering was: Why do the cookies get hot enough to bake in a car on a hot summer day and why extreme heat is being experienced differently among some racial and ethnic groups? 

The explanation layers three important aspects: 

In the summer in Phoenix, cars parked in the sun can reach temperatures significantly higher than the surrounding air. People can even bake cookies in their cars. This phenomenon occurs because of several different ways heat is transferred and trapped.

To begin with, the heat baking cookies in the car comes from the energy released by the sun. In the Newsela Reading Jigsaw activity, we learned that the emission and transmission of energy through lights, including visible and invisible lights, is called radiation. Every object with a temperature greater than absolute zero can emit lights. By temperature we mean a measure of the average kinetic energy of particles of an object. Particles vibrate with kinetic energy, and the higher the temperature, the faster the vibrations are. Energy transferred naturally from an object with a higher temperature (a hotter body) to an object with a lower temperature (a cooler body), and the temperature of objects would change. In the Transfer of Thermal Energy video, we saw what happens among particles when energy is transferred from a hotter object to a colder object and the temperature of the object changes. When a hot object touches a cold one, the particles (molecules) in each collide. When this occurs, the particles from the hot object pass on some of their energy to the particles in the cold object. In our case, the sun is the primary radiating body that heats the earth. Since the sun has extremely high temperature, it emits many kinds of light, and the main component of that light that heats the earth is infrared light, which causes molecules of objects on earth to vibrate faster. Thus, when light hits the car, energy is absorbed by the interior surfaces and objects of the car, such as the dashboard, seats, and steering wheel. Those surfaces and objects get much hotter and then re-emit radiation, causing the temperature in the car to rise. We know this because in the Thermal Map of Our School activity, we measured the temperature of our school, and found out that the parts that are exposed to the sun, such as the football field and exterior walls, are hotter than the shaded areas and emit stronger infrared radiation.

Subsequently, the air inside the car is heated by both the sun and these metal and plastic surfaces of the car through conduction and convection. In the Heat the Soda Can and Flowing Energy activities, we saw how the colors of cold and hot water diffuse and mix, which indicates how energy is transferred. We know that conduction and convection, as well as radiation, are ways of energy transfer. Still, energy is transferred from objects with higher temperatures to objects with lower temperatures in all the three ways. Specifically, conduction occurs between objects that are touching, like the dashboard heat cookies, and convection refers to the flow of energy through a liquid or gas, such as interaction of air molecules within the car.

Following this, as the interior temperature of a car rises, the car also emits radiation thus releasing heat to the surroundings. However, since the sun is much hotter than the car, the rate of car’s radiation is much lower than the rate of sun's radiation. Besides, in the Greenhouse Stimulation Lab, we learned that windows act as a barrier, preventing the escape of infrared light, so the radiation is trapped inside the car, like the energy is trapped on earth. As a result, the car absorbs and traps energy from solar radiation, contributing to the hotter environment in the car. 

Finally, as the temperature in the car increases, it is hot enough for baking cookies. Cookies receive energy through conduction and convection from heated surfaces and air inside the car and being baked.

This phenomenon is not exclusive to cars. Similar phenomena - hotter internal environment - exist in many human-made surfaces, such as buildings, roads, and parking lots. As a result, several urban areas are much hotter than outlying areas. However, in the Heat in Cities activity as well as from the experience of our friends, we know that not everyone experiences extreme heat equally. The way a person experiences extreme heat is at least partially linked to race and class. For example, racially and socioeconomically marginalized neighborhoods have a larger proportion of impervious ground and a smaller proportion of tree shade. Such neighborhoods bear heavier traffic, more polluting industries, and weaker infrastructure construction. Residents there not only are forced to endure higher temperatures, but also find it difficult to cool down in green space. Therefore, lower-income, disproportionately Black and Latino neighborhoods are among the most vulnerable to heat health risks.

Important to a scientific explanation is that it is causal.  In other words, explanations should answer "why" the anchoring event happened. The "why" is often invisible, occuring at a microscopic level or over large amounts of time. Below is a great resource from the Ambitious Science Teaching group on moving students from simple "what" explanations to "why" or fully causal explanations.

Overview-WhatHowWhy-Rubric-for-Evaluating-Student-Explanations.pdf

In our MBI template, you are asked to write two different example explanations. The first, the 'Target Written Explanation', is a fully causal accounting of the story. To be a fully scientific explanation, the important science ideas (e.g., natural selection, convection currents, radioactive decay, etc.) should be integrated into the explanation. This target written explanation will help you identify the important science ideas to structure your unit around.

The second explanation occurs in Stage 5 of the template where you are asked to write an example 'Final Evidence-Based Explanation'. This is similar to the target written explanation, but it also include statements connecting the claims to specific pieces of evidence collected during the tasks. It is a fully causal story of the phenomenon, integrates the important science ideas at play during the unit, and provides the evidence for how we came to understand the explanation. This is merely an example of what students could produce. The students will find multiple ways to write their own explanations!

What counts as evidence?

For a final evidence-based explanation at the very end of the MBI unit, we want students to not only provide a causal account of the anchoring phenomenon, but to support their explanation with evidence. In science, evidence is most often quantitative or qualitative in nature. This is the same for the science classroom.  For example, student investigations of the soda can crushing lab will lead to quantifiable data about the relationship between temperature and pressure to use as evidence in the explanation of the tanker implosion phenomenon. However, especially at younger grades, we can use specific activities as evidence. For example, in building our explanation of the impact of the reintroduction of wolves into Yellowstone, the Oh Deer activity helps us understand the concept of carrying capacity and limiting factors. See our Evidence-Based Explanation Rubric below for ways we think about assessing students' final evidence-based explanations at the end of the unit.

MBI_Rubric.pdf

Additional Resources