The cognitive science behind teaching science shows that abstract ideas should be connected to concrete examples to maximize understanding. Energy is an abstract concept, yet little analysis of how to best connect energy to concrete examples exists. The experiences of teaching both chemistry and physics have provided me some insights into what teachers should do to help students understand scenarios that have traditionally been analyzed using energy.
Motion, position and force are more concrete (less abstract) than energy. Whenever possible energy should be removed from the explanation or discussion and replaced with these. When students use energy with regards to kinetic or gravitational potential energy they have an easier time processing new information. Asking students which has a larger kinetic energy when comparing an object at different speeds is easily transferable between the abstract energy and the concrete speed. The other two forms of energy that are easily visible for students are spring energy and gravitational potential energy.
Showing students a relaxed spring and a compressed spring allows them to easily identify that the compressed spring has more energy. Holding a marker a meter off the ground and two meters off the ground easily allows them to identify that the two meter mark has more potential energy. The reason why this is easily analyzed by students is that they easily connect to the concrete. The students can see that upon release, more motion results from the compressed spring and the elevated marker. Note that for both instances the concrete image of fast moving objects is easily accessible. In Figure 1 below, it is obvious that when released object B will be moving faster right before it hits the ground than object A.
Figure 1: Two objects where object B is twice the distance from the ground that object A is
When is it not clear?
Energy remains obscure with charged particles and electrical energy. A simple explanation is that charged particles have two competing abstract ideas visible to students. When a proton and electron are close together the students understand that there is a larger force between them than when they have a large separation. But these particles have less energy than particles that are separated. To reconcile these two competing ideas it can be helpful to track the relative speeds. If an electron and proton are separated by a distance and released, they will move towards each other and collide (ignoring quantum physics). If the electron and proton are now separated to twice the distance, they will approach and collide, but at a higher speed than before. When they reach the original separation they will have that kinetic energy gained plus the same potential energy as before.
Figure 2: Top two charges start separated by a distance d. Middle two charges start separated by a distance 2d. Bottom two charges started at a distance 2d but have moved to a distance of d and are now moving with a relative speed.
It takes time for students to connect the ideas present in Figure 1 above. Often in chemistry we exacerbate this by labeling the potential energy without specifying whether it is potential or kinetic. The middle set of charges has more energy than the top set of charges. This is difficult for students because they see the forces as being larger for the top set and have experienced the stronger attraction when playing with magnets.
This is not as problematic with gravitational potential energy because the force of gravity is relatively constant because of the small change in distance relative to the large separation from the center of the earth. Students also have substantially more sensory experience with gravitational interactions then electric.
Energy by definition should be linked to a force. Energy and work have circular definitions, but the mathematical origins of energy are an integral of a force over a pathway. For example, gravitational potential energy (mgh) is derived from the integration of weight (mg) for the pathway of separation between the two objects. This conflicts with the presentation of energy in science classrooms frequently. Chemical energy, sound energy, “heat” energy and many other forms of energy are not directly linked to a fundamental force. Chemical energy for example is based on electrical forces. “Heat” energy or thermal energy is based on kinetic energies of particles.
By introducing energy in terms of conservation of these forms that do not have a direct link to a force, we obfuscate the underlying abstract definition of what energy is. This conflict allows students (and teachers) to maintain a wide variety of mental models of what energy is. The current push for developing models of energy in the NGSS is insufficient to undermine and may actually reinforce the problem.
Figure 3: NGSS that deal with energy, taken from https://www.nextgenscience.org/topic-arrangement/4energy on 1/9/2020
In Figure 3 we see the idea of conservation as fundamental to 4-PS3-2, 4-PS3-4 and 4-ESS3-1. 4-PS3-1 shows some promise but also undercuts that potential by making this a mathematical connection instead of dealing with the conflicts discussed above. None of these set up for students to challenge the underlying struggle of unpacking why electrical energy increases as separation between charges gets larger.
How should teachers attack this misconception?
An abstract idea is understood better when multiple concrete examples are used. A strategy that I have found helpful for this is to limit energy in education. Every scenario that is explained using energy can also be explained using force, position and motion instead. By eliminating energy from the explanation you require a concrete connection to be the impetus for understanding. This is challenging and often unique. Could you explain how digestion works without using energy in your explanation? Could you talk about how light and electrons interact without using energy? Can we differentiate a nuclear power plant and a coal one without energy? The answer to this is always yes, but it requires practice.
Chemical Reactions
Energy in chemical reactions can be presented in many formats. One common format is using reaction energy diagrams. A reaction energy diagram is extremely abstract. The abstraction can be reduced using simple diagrams for a reaction. With a very generic reaction energy diagram teachers can communicate simple abstract ideas to students without the student being forced to develop a concrete example. Teachers can highlight that the potential energy of the chemical system has increased as the reaction proceeds in Figure 4.
Figure 4: A generic endothermic reaction energy diagram.
Figure 5 is an improvement because it allows students to develop the idea that transition states are unstable. This makes some intuitive sense to the student that the more common representation of a bond is stable. But in order to really advance the model for students one must address the underlying potential misconceptions. This is to be done by marking down how the forces, positions and motions all relate to one another.
Figure 5: Particle representations that show the reaction transitional state where bonds have broken but not yet reformed.
From the initial reactant state to the transition state, B moves away from A. A and B are attracted to each other so the forces are inwards while the motion of A and B is outward. In order for A and B to move apart while forces pull them together, they have to slow down. If you are moving left, and being pulled right, your speed lessens. What we’re describing here is a transition from kinetic to potential energy. When a collision occurs that causes a large relative motion between A and B, A and B can separate. But to do so they slow down. If a small collision occurs, A and B will start to separate but will revert back to their bonded state before completing the separation.
When C and B approach each other the force is again inwards. But now B and C are approaching each other. Their motion and their forces are aligned and so their speeds increase. As the bond forms their speeds increase and later that increase in motion could be transferred back to the surroundings through collisions (heat). Note how by analyzing this without energy the student is not going to develop the biology misconception that breaking bonds releases energy. Students often see the transition from ATP to ADP as a bond breaking that releases energy and retain this idea in chemistry and physics. When ATP turns into ADP it is not a single bond change that occurs. Here the students can logically process that the particles are going to slow down as bonds break and speed up as bonds form. Now when a reaction is endothermic they can infer that the bonds were harder to break. When a reaction is exothermic the initial bonds were easier to break and the particles sped up more than they slowed down. A video breakdown of this schematic can be found here.
Digestion
Why do you eat food? Because it gives you energy. How does photosynthesis work? Plants turn light into energy. The questions and answers that surround digestion are filled with abstract hand waving. I am not a biology expert so if my explanations are flawed, please try and focus on the development rather than the specifics.
When you consume food your body changes that food into smaller pieces and distributes those pieces throughout your body. Much of that food turns into a sugar called glucose. Cells use glucose by burning it. The glucose reacts with oxygen and as this happens the products of the reaction move faster than the initial speeds of the glucose and oxygen. That motion is used to push other chemicals together in a way that forms something called ATP from ADP. The ATP and ADP can be used to cause muscle contraction because the charges of the ATP and ADP cause muscle fibers to grab hold, pull on muscle fibers, release and reset. These actions results from the changes in charge distribution within the ADP and ATP that result from the reactions of the glucose changing.
If the initial warning wasn’t sufficient, the preceding paragraph makes clear that I have a limited understanding of the cycles used as well as the chemicals involved as intermediates. But in reading this many questions that could undermine my ignorance become clear. How does the burning of glucose in cells differ from the combustion that occurs in air? When the conversion forms an unstable intermediate, how does charge distribution play a role? How does the cell distribute these unstable intermediates without a reversion to a more stable set of chemicals? What in the structure of myosin and actin leads to a binding interaction and how is that interaction disrupted? What about its structure makes ATP so effective at distributing charge that causes other molecules to move? Many of these questions have an underlying theme. Charge is being used to push or pull and motion is being used to initiate those pushes and pulls. A biochemistry expert should be able to detail how the chemicals at each stage of digestion leads to the desired result and they should be able to do so without using energy.
Photosynthesis is very similar but light presents a new struggle. How do we describe light without using energy? Light originates when charged particles change. The exact changes are difficult to describe because charged particles are too small to observe in the same way we view macroscopic objects. We could say that when charged particles change how they move light is produced, but that is probably not completely true and not completely false either. Light originates from a charged particle (electron, nucleus, etc.) and terminates when the light causes a different charged particle to change its state.
When light hits a chemical, the light can interact with the electrons in that chemical. The resulting changes for the electron that absorbs the light can result in new positions and motions for the electron that change the attractive forces within the molecule. This can lead to attractions being disrupted. The resulting unstable intermediates and transition states can lead to collisions where other molecules are pulled on. Photosynthesis is where light hits a chlorophyll pigment that causes changes to the electronic structure. The changes to the chlorophyll have various pathways that end up using that change to pull particles where the eventual result is combining carbon dioxide and water into sugars. Sometimes the chlorophyll can remove electrons from water molecules that then turn into protons and oxygen. The protons (H+ ions) can build up forming a charge gradient along a wall. Again the details are bit beyond my expertise level but hopefully you can begin to see how an expert would be able to replace the term energy within each of these steps with the result in terms of charge distribution, motion and position.
Power Plants
When we say that we have an energy crisis, what do we actually mean? What specific things do we mean that we could replace the term energy with? The often mean electricity. We could also be talking about fuels or stuff that burns.
Nearly all power plants function with the same underlying principles. You have to make a turbine spin fast. When the spinning is connected with a magnet inside a coil of wires you get electricity. The big differences in how the spinning is produced is the primary difference between electricity production. Fossil fuels (coal, oil, methane) are burned underneath a vessel filled with water. As the water turns into steam, the steam particles collide with the blades of a turbine causing it to spin. A nuclear power plant functions in the exact same manner but instead the uranium rods are inserted into the water to heat the water instead of burning fuel. Hydroelectricity uses water to push on turbine blades. Wind turbines are arranged where wind is likely to push more in one direction than another.
Note how whenever we eliminate the word energy from explanations the details become more concrete. The uranium fuel rods provide energy that heats the water. The uranium particles in the fuel rods split into pieces that move fast. As they fly through the water they drag water particles causing the water to speed up. Fossil fuels provide energy to heat the water. Fossil fuels react with oxygen and after the reaction the products move at higher speeds. When these fast moving particles collide with the vessel containing the water the collisions tend to transfer motion to the water particles.
Conclusions
Energy allows us a lot of mental and mathematical shortcuts in science that are valuable. Explaining and understanding quantum mechanics without energy is a burden that would exclude many from the field. But there is a cost to using energy. Using energy as an explanation results in less understanding and that cost is too great in science education. Strategies to make energy less abstract include:
1. Explain processes without using the term energy. Use force, motion and position to help guide the explanations.
2. When using energy, it should tie directly to a force (gravity, electric, magnetic, nuclear). Avoid terms like sound energy, heat energy and chemical energy.
3. When something is too complicated to explain without energy, try and split the process into fragments. What do I have at the beginning, middle and end. Can I explain any of these transitions without energy?
4. Explanations in chemistry must address the misconception that forces and energy are interchangeable for charged particles. Large separations have small forces and high energies.5. Particle level representations can help expose incomplete details.
6. Anticipate having students that ask “How do you know that the energy changes that way?” prior to the lesson and work on answering that question.
7. Be wary of changing forms of energy. Changing forms is useful for calculation simplification but is highly disruptive to student understanding.
8. When avoiding energy, it is critical to reduce the number of tier 2 and tier 3 vocabulary terms to avoid cognitive overload. Keep everything else simple.
9. Biology is the hardest subject to do this in. Sometimes though the energy components do not contribute anything of value. ATP changing to ADP allows muscles to contract. Do I need to use energy in that observation? Does it enhance the understanding?
Practice is required to improve at avoiding energy in science education. When teachers feel inadequate to continue they should write down questions they have to see if there is a potential resolution. Teachers should be wary of science education techniques that organize energy into models. This often takes the abstract concept of energy and avoids the ability to make it concrete.
