# 12 Overview of the Types of Energy and Its Conservation

Brokk Toggerson and OpenStax

If you look in high-school science textbooks, they will often list a myriad of energy types: chemical, thermal, kinetic, nuclear, … However, by now you know that physics is all about distillation: finding the fewest number of fundamental rules needed to explain the universe. So, are there underlying commonalities among all these different types? In short, yes! This chapter will explore these underlying patterns and provide a brief overview of the different types of energy we will consider in this course. Later chapters will then explore each type in a bit more detail.

# How Many Kinds of Energy Are There?

Two. Ultimately, all the aforementioned types of energy (chemical, thermal, kinetic, nuclear, …) boil down to just two different kinds: kinetic energy and potential energy. is the capacity to do work (push or pull on something for a distance) arising from an object’s motion. is then the capacity to do work due to the relative positions of different objects within a system. Let’s look at these two categories in detail.

## Kinetic Energy

Below is a video providing an overview of kinetic energy. The information is presented as video as there are demonstrations within. As with many of the videos you will see in this book, the demonstrations use materials that you probably have access to. I would encourage you to get the materials and actually repeat the experiments at home!

Below is the simulation I showed in the video. You are encouraged to play with it yourself.

## Potential Energy[1]

What if we lift a motionless wrecking ball two stories above a car with a crane? If the suspended wrecking ball is unmoving, can we associate energy with it? The answer is yes. The suspended wrecking ball has associated energy that is fundamentally different from the kinetic energy of objects in motion. This energy form results from the potential for the wrecking ball to do work. If we release the ball it would do work. Because this energy type refers to the potential to do work, we call it potential energy. Objects transfer their energy between kinetic and potential in the following way: As the wrecking ball hangs motionless, it has 0 kinetic and 100 percent potential energy. Once it releases, its kinetic energy begins to increase because it builds speed due to gravity. Simultaneously, as it nears the ground, it loses potential energy. Somewhere mid-fall it has 50 percent kinetic and 50 percent potential energy. Just before it hits the ground, the ball has nearly lost its potential energy and has near-maximal kinetic energy. Other examples of potential energy include water’s energy held behind a dam, or a person about to skydive from an airplane.

We associate potential energy not only with the matter’s location (such as a child sitting on a tree branch), but also with the matter’s structure. A spring on the ground has potential energy if it is compressed; so does a tautly pulled rubber band. The very existence of living cells relies heavily on structural potential energy. On a chemical level, the bonds that hold the molecules’ atoms together have potential energy. Remember that anabolic cellular pathways require energy to synthesize complex molecules from simpler ones, and catabolic pathways release energy when complex molecules break down. That certain chemical bonds’ breakdown can release energy implies that those bonds have potential energy. In fact, there is potential energy stored within the bonds of all the food molecules we eat, which we eventually harness for use. This is because these bonds can release energy when broken. Scientists call the potential energy type that exists within chemical bonds that releases when those bonds break chemical energy. Chemical energy is responsible for providing living cells with energy from food. Breaking the molecular bonds within fuel molecules brings about the energy’s release.

### Why do we care about springs?

In the prior section, we discussed springs as having a potential energy. You may be asking yourself, “I am a life-science student! I don’t care about metal coils, why are we studying them?” This is a good question. The reason we will spend a lot of time studying springs in this course is that many different materials can be modeled by a spring. Some good examples are:

• Tendons – They pull back when stretched. The presence of this restorative force in our Achilles tendons makes us more efficient runners!
• DNA and other molecular bonds – Molecular bonds work very much like springs: when stretched they pull back, and when compressed they push against that push. Molecules even oscillate (bounce back and forth) as though each atom is connected to a spring as shown in the video below.
A video showing how molecules can be modeled by springs.

Below is the simulation used in the prior video. I would encourage you to play with it to get a feel for how molecules can be modeled by springs!

# Conservation of Energy[2]

Energy can be converted from one form into another, but all of the energy present before a change occurs always exists in some form after the change is completed. This observation is expressed in the law of conservation of energy: during a chemical or physical change, energy can be neither created nor destroyed, although it can be changed in form. (This is also one version of the first law of thermodynamics, as you will learn later.)

When one substance is converted into another, there is always an associated conversion of one form of energy into another. Heat is usually released or absorbed, but sometimes the conversion involves light, electrical energy, or some other form of energy. For example, chemical energy (a type of potential energy) is stored in the molecules that compose gasoline. When gasoline is combusted within the cylinders of a car’s engine, the rapidly expanding gaseous products of this chemical reaction generate mechanical energy (a type of kinetic energy) when they move the cylinders’ pistons.

## An example of conservation of energy using a simulation

Below is the simulation used in the video above. Play along!

Example – Conservation of Energy

Problem

A typical gasoline tank for a car has of energy. Let’s say that a car is initially coasting on a flat surface with of kinetic energy, when all the gasoline has been burned, how much kinetic energy do you expect the car to have?

Solution

We are using the idea of conservation of energy above. We have of energy in gasoline and of kinetic energy for a total of

Since the total amount of energy cannot change, this is the amount of kinetic energy that the car must have after all the gasoline has been burned:

Homework

• Energy types described mathematically in this course.

1. Clark, M. A., Douglas, M., & Choi, J. (2018). 6.2 Potential, Kinetic, Free, and Activation Energy. In Biology 2e. OpenStax.
2. Flowers, P., Neth, E. J., Robinson, W. E., Theopold, K., & Langley, R. (2019). Energy Basics. In Atoms First 2e (p. 9.1). OpenStax.