Definition of Energy (Simple and Illustrated)

English Vocabulary Lesson

In this lesson, we share an easy definition of energy. We will use examples and pictures to help us understand the different meanings and uses of this important word.
definition of energy

1) Everyday Definition of "Energy"

Energy is the ability to do a physical or mental activity. The less energy you have, the more tired or exhausted you are. The more energy you have, the more you feel alert, strong, and alive.
high energy
For example, you might say "I don't have the energy to go running today". This means you feel you don't have enough "power" (ability, strength) to do physical activity.
lack of energy
Similarly, if you are feeling mentally drained, you might say "I don't have the energy to focus on this task". Here, you are saying you feel you don't have the mental strength required to complete the task.


Example Sentences (Negative)

  • "I don't have the energy to clean the house today. I'm just too tired."
  • "I don't have the energy to go out tonight. I think I'll just stay home and rest."
  • "I don't have the energy to study for this exam. It's so late at night that I'm unable to focus."
  • "I don't have the energy to deal with this problem right now. Can we talk about it later?"
  • "I don't have the energy to play with our dogs today. I need to take a break."

Example Sentences (Positive)

  • "I'm full of energy today. I'm ready to tackle any task that comes my way!"
  • "I'm feeling really energized today. I have the energy to go for a long hike!"
  • "I feel so alive. I have the energy to play with our dogs and run around the park with them!"
  • "You seem especially motivated today. Do you have the energy to work on this project and see it through to completion?"


2) Scientific Definition of "Energy"

Energy is the ability to do work or produce change.

For example:

When you lift a heavy object (or any object), you use energy (apply force to move the object).
When you run or walk, you use energy (apply force to move your body).


Energy can take many forms:

Kinetic energy (the energy of motion): The force of a moving object.

Imagine a bowling ball sitting on the floor. The ball is not moving, so it does not have any kinetic energy.
Now, imagine that you pick up the ball and roll it down a lane toward a group of pins. As the ball rolls, it gains kinetic energy because it is moving.
When the ball hits the pins, it transfers some of its kinetic energy to the pins, causing them to move and fall. The force of the moving ball to do work, such as knocking down the pins, is a result of its kinetic energy.
Kinetic energy (the energy of motion)


Potential energy (the stored energy of an object):
the force an object has because of its position, or the forces acting upon it. The higher an object is, the more potential power it has. The more forces acting on an object, the more potential power it has.

Imagine a book sitting on a shelf. The book has potential energy because it is being held up by the shelf, and if the book were to fall, it would hit the floor with force. The higher the book is on the shelf, the more potential energy it has because it has a greater distance to fall.
Potential energy (the stored energy of an object)

Or, imagine a rubber band stretched between your feet. The rubber band has potential energy because it is being stretched and held in place. If you let go of the rubber band, it will have the power to snap back with force into its original shape.
Potential energy (the stored energy of an object)


Thermal energy (heat):
the force that an object has due to the movement of its particles. The faster the particles in an object move, the more thermal energy the object has (the object is hotter).

Imagine a cup of hot tea. The tea has thermal energy because the particles in the tea are moving around and colliding with each other.
As the tea heats up, the particles in the tea move faster, increasing the thermal energy of the tea.
When you touch the cup, you can feel the heat being transferred from the tea to your hand. This is an example of how thermal energy can be used to do work, such as warming up your hand.
Thermal energy (heat)


Electrical energy (the energy of electricity):
the force of electrons moving through a substance (like copper wire). Electrical energy can be used to do work, such as powering a light bulb or a motor.

For example, when you turn on a light switch, the electrons in the wires are pushed along by a force (electricity) to power the light bulb. The electrical energy produced by the movement of these electrons is used to do work (illuminate the room).
Electrical energy (the energy of electricity)


Chemical energy (the energy stored in substances): the force that binds atoms together. Chemical energy is stored inside substances. When these substances are mixed or changed in some way, the chemical energy is released. This energy can be used to do work or create change.

For example, when a match is struck, the chemical energy inside the match is released. This energy creates heat and light (fire), which can be used to do work (such as lighting a candle).
Chemical energy (the energy stored in substances)


Solar energy (the energy from the sun):
the force that comes from our closest star, the Sun. Solar energy is used to do work, such as powering a car or providing light and heat to our homes.

For example, when solar panels are exposed to sunlight, they convert the solar energy into electrical energy. This electricity can then be used to do work, such as powering a light bulb or a motor.
Solar energy (the energy from the sun)

Another example is when our bodies are exposed to sunlight, it produces heat (warms us up).
There are additional kinds of energy, such as mechanical energy, among others. (Mechanical energy is the energy an object has due to its movement or position. It is the total energy of an object that is related to its movement and how high or low it is. For example, a pendulum has mechanical energy when it is swinging.)
Mechanical energy


Example Sentences

  • "The sun produces a lot of energy, which we can use to generate electricity."
  • "I picked up a heavy box, and it took a lot of energy to lift it."
  • "The car's engine converts gasoline into energy, which powers the car's movement."
  • "The battery stores energy, which can be used to power a flashlight."
  • "Plants use sunlight to convert energy from the sun into chemical energy."
  • "The ball transferred some of its kinetic energy to the pins, causing them to move and fall."
  • "The book had potential energy because it was being held up by the shelf."
  • "The tea had thermal energy because the particles in the tea were moving around and colliding with each other."
  • "The electrical energy produced by the movement of electrons was used to illuminate the room."
  • "When a match is struck, the chemical energy inside the match is released."
  • "Solar panels convert solar energy into electrical energy, which can then be used to do work."


A Dialogue to Practice Using the Word "Energy" in Context (Everyday Meaning)

Alex: Hey, how was your workout this morning, Samantha?

Samantha: It was great! I had so much energy after my breakfast.

Alex: That's awesome! I wish I had that much energy in the morning.

Samantha: Yeah, it really helps to start the day off right. Do you have any plans for the rest of the day?

Alex: Not really. I was thinking of taking it easy and just relaxing at home.

Samantha: Well, if you're feeling low on energy, that's a good idea. It's important to listen to your body and give it the rest it needs.

Alex: Yeah, you're right. I'll just take a nap to recharge my energy. Otherwise, I won't have enough mental energy for that task later on.

Samantha: Good idea. You'll be feeling refreshed and ready to tackle anything. Have a good rest!

A Dialogue to Practice Using the Word "Energy" in Context (Scientific Meaning)

Scientist 1: Hey, I heard you have been working on improving the energy efficiency of car engines. How's it going?

Scientist 2: It's going well! We've been testing different designs and materials to see which ones can optimize the energy conversion in the engine.

Scientist 1: That's interesting. What kind of energy conversion are you looking at?

Scientist 2: We're mainly focused on improving the efficiency of the internal combustion process. That's where the energy from the fuel is converted into mechanical energy to power the car.

Scientist 1: I see. And have you made any progress?

Scientist 2: Yeah, we've made some good strides. We've been able to increase the energy conversion efficiency by about 5% by using a new type of fuel injection system.

Scientist 1: That's great! Any increase in energy efficiency is always a positive step.

Scientist 2: Definitely. We're always looking for ways to reduce the amount of energy wasted in the process and make the most of the resources we have.

Scientist 1: So, what's next on your list of improvements?

Scientist 2: We're planning on experimenting with different types of fuels to see if we can find one that has a higher energy density and burns more efficiently.

Scientist 1: That's a good idea. Higher energy density means more energy can be stored in a smaller space, right?

Scientist 2: Exactly. And a more efficient burn means less energy is lost as heat and more of it is converted into usable mechanical energy.

Scientist 1: It sounds like you're making some significant progress in optimizing the energy conversion in car engines.

Scientist 2: Yeah, we're definitely making progress. But there's always more to be done. There are always new technologies and materials to explore, and there's always room for improvement.

Scientist 1: I agree. It's important to keep pushing the boundaries and finding new ways to increase energy efficiency.