Energy: Introduction and Overview
Day 1 of 5 — What Is Energy?
Learning Objectives
Define energy as the ability to do work or cause change
Identify and describe the major forms of energy: thermal, light, sound, electrical, chemical, and mechanical
Distinguish between kinetic energy and potential energy and provide examples of each
Explain that energy can change forms but is never created or destroyed
What Is Energy?
~5 minutesImagine a world where nothing moves, nothing glows, nothing makes a sound, and nothing grows. That world would be a world without energy. Energy is one of the most important concepts in all of science. It is the reason a ball bounces, a light bulb glows, your body stays warm, and music plays from a speaker. In this unit, we will explore what energy is, the different forms it takes, how it moves from one place to another, and why it can never be created or destroyed.
Energy is the ability to do work or cause change. In science, 'work' has a specific meaning: work is done when a force causes an object to move. Whenever something moves, heats up, cools down, lights up, makes noise, or changes in any way, energy is involved. The scientific unit for measuring energy is the joule (J), named after the English physicist James Prescott Joule.
Kinetic vs. Potential Energy
~7 minutesAll energy falls into two broad categories. Kinetic energy is the energy of motion. Any object that is moving, whether it is a speeding car, a vibrating guitar string, or the molecules bouncing around inside a hot cup of cocoa, has kinetic energy. The faster something moves, or the more mass it has, the more kinetic energy it possesses.
Potential energy is stored energy. It is energy that an object has because of its position, shape, or chemical makeup. A book on a high shelf has gravitational potential energy because it could fall. A stretched rubber band has elastic potential energy. The food you eat contains chemical potential energy that your body converts into motion and heat.
Check Your Understanding: KE vs. PE
~5 minutesA roller coaster car sitting at the very top of the tallest hill, right before it begins to drop, has:
Which of the following are examples of potential energy? (Select all that apply)
Select all that apply.
A ball is thrown straight up into the air. Arrange these stages in order from FIRST to LAST, and think about how kinetic and potential energy change:
Six Forms of Energy
~7 minutesEnergy exists in many forms, and each form is related to either motion or position:
Thermal energy is the total kinetic energy of all the tiny particles (atoms and molecules) inside a substance. The faster the particles move, the hotter the substance feels.
Light energy (also called radiant energy) is energy carried by electromagnetic waves. The sun is our biggest source of light energy.
Sound energy is produced when an object vibrates, creating waves that travel through air, water, or solids.
Electrical energy comes from the movement of electrically charged particles called electrons. It powers nearly everything in our homes.
Chemical energy is stored in the bonds between atoms in molecules. Food, batteries, and gasoline all contain chemical energy.
Mechanical energy is the combination of kinetic and potential energy in a moving or positioned object. A swinging pendulum has mechanical energy.
Check Your Understanding: Forms of Energy
~4 minutesWhat is the scientific definition of energy?
A student eats a granola bar before going for a run. What energy transformation is happening?
Match each example to the primary form of energy it demonstrates:
Energy Transformations and Conservation
~8 minutesEnergy Transformations
One of the most fascinating things about energy is that it constantly changes from one form to another. Scientists call this an energy transformation (or energy conversion). A car engine transforms chemical energy in gasoline into mechanical energy (motion) and thermal energy (heat). A flashlight transforms chemical energy in the battery into electrical energy, then into light energy. Your body transforms chemical energy from the food you eat into mechanical energy (so you can move) and thermal energy (which keeps your body at about 37 degrees Celsius).
In every transformation, energy is never created and never destroyed. It simply changes form. This principle is called the law of conservation of energy, and it is one of the most fundamental laws in all of science.
Energy cannot be created or destroyed. It can only change from one form to another or transfer from one object to another. The total amount of energy in a closed system always stays the same. When it seems like energy has 'disappeared' (like when a ball stops bouncing), it has actually been transformed into thermal energy (heat) through friction.
Check Your Understanding: Transformations & Conservation
~7 minutesEnergy can be created when we turn on a power plant and destroyed when we use it up.
When a bouncing ball gradually stops bouncing, what happened to its energy?
Describe one energy transformation that happens in your everyday life. Identify the starting form of energy, the ending form(s) of energy, and explain how this demonstrates the law of conservation of energy.
Expected length: 40-150 words
Looking Ahead
~2 minutesThis introduction gives you the big picture of energy. Over the rest of the week, we will: explore each form of energy in depth (Tuesday), investigate how thermal energy transfers through conduction, convection, and radiation (Wednesday), discover what makes materials conductors or insulators and build circuits (Thursday), and bring everything together with the law of conservation of energy (Friday).