Energy in physics. Concepts, main forms, and law of conservation of energy
The online energy simulations on this page will help you understand what energy is in physics, its main forms, such as kinetic energy and potential energy, and how it is transformed from one form to another. We will also explore the law of conservation of energy and its applications in different physical phenomena
This Thematic Unit is part of our Physics collection

STEM OnLine mini dictionary
Conservation Principle
Law stating that the total energy of an isolated system remains invariant, transforming but not being destroyed.
Energy
Capacity of a physical system to perform work or produce changes, measured in the International System in joules (J).
Energy Dissipation
Transformation of kinetic energy into heat due to the work performed by the friction force.
Gravitational Potential Energy
Energy that depends on an object’s height relative to a reference level and the force of gravity.
Isolated System
Physical system that does not exchange matter or energy with its environment, keeping its total energy constant.
Joule
Unit of energy and work equivalent to the work performed by a force of one newton acting over a distance of one meter.
Kinetic Energy
Energy possessed by a body due to its motion, dependent on its mass and the square of its velocity.
Mechanical Energy
Sum of the kinetic energy and potential energy of a body or system in a given state.
Potential Energy
Energy stored in an object due to its position or configuration within a field of forces.
Watt
Unit of power representing the transfer or consumption of one joule of energy per every second of time.
What is energy in physics
Energy in physics is a fundamental property of nature defined as the capacity of a system to perform work. It manifests itself in virtually all physical phenomena, from the movement of bodies to thermal, electrical, or chemical changes. Understanding energy allows us to explain how processes occur and transform in the universe, and provides the basis for analyzing any physical system, from a ball in free fall to the energy stored in atoms and molecules.
Forms of energy in physics
Energy can take many forms, such as the well-known kinetic energy or potential energy, or the lesser-known thermal energy, electrical energy, and chemical energy. Each of these forms manifests itself in different physical or chemical phenomena and processes, and in many cases can be transformed from one form to another. This capacity for change, together with the law of conservation of energy, explains how energy moves and transforms in nature and in the technology we use every day.
Kinetic energy
Kinetic energy is the energy a body possesses due to its motion. The greater the mass of the object and the faster its speed, the greater its kinetic energy. For example, a moving car or a thrown ball has kinetic energy because it is moving.
Potential energy
Potential energy is the energy stored in an object due to its position or configuration within a force field, such as gravitational or elastic. For example, a ball at the top of a hill has gravitational potential energy, because when it is released it can be transformed into kinetic energy as it descends. This form of energy depends on both the height or position of the object and the force acting on it.
Other forms of energy
In addition to kinetic energy and potential energy, there are other forms of energy that manifest themselves in different physical and chemical phenomena. Thermal energy is associated with heat and the microscopic movement of particles in a body. Electrical energy is related to the presence and flow of electrical charges, and chemical energy is stored in the bonds between atoms and molecules, being released or absorbed in chemical reactions.
Law of conservation of energy
The law of conservation of energy is one of the fundamental principles of physics. It states that the total energy of an isolated system, i.e., a system that does not exchange energy with its surroundings, remains constant over time. This implies that energy cannot be created or destroyed, only transformed from one form to another.
For example, when an object falls, the gravitational potential energy it possesses due to its height is progressively converted into kinetic energy associated with its movement. If we consider the entire system, the sum of both energies remains constant, regardless of temporary losses due to friction or other internal forces.
This principle applies to all types of physical systems, from a simple pendulum to complex mechanisms such as engines, electrical circuits, or chemical processes, and forms the basis for understanding how energy is conserved and distributed in nature.
Energy applications
Energy is a central concept in virtually all areas of science and technology. It allows us to describe and analyze phenomena as varied as heat transfer, the movement of bodies, chemical reactions, and electricity generation.
Understanding energy is essential for designing and optimizing modern technologies, from engines and power plants to electronic devices and transportation systems. Furthermore, knowing how energy is transformed and conserved is key to developing sustainable and efficient solutions that enable us to meet current and future energy challenges, including the use of renewable sources and the reduction of environmental impact.
The study of energy is also essential in science education, as it provides a common framework for understanding different physical and chemical phenomena, facilitating the transition between abstract concepts and practical applications.

STEM OnLine mini dictionary
Conservation Principle
Law stating that the total energy of an isolated system remains invariant, transforming but not being destroyed.
Energy
Capacity of a physical system to perform work or produce changes, measured in the International System in joules (J).
Energy Dissipation
Transformation of kinetic energy into heat due to the work performed by the friction force.
Gravitational Potential Energy
Energy that depends on an object’s height relative to a reference level and the force of gravity.
Isolated System
Physical system that does not exchange matter or energy with its environment, keeping its total energy constant.
Joule
Unit of energy and work equivalent to the work performed by a force of one newton acting over a distance of one meter.
Kinetic Energy
Energy possessed by a body due to its motion, dependent on its mass and the square of its velocity.
Mechanical Energy
Sum of the kinetic energy and potential energy of a body or system in a given state.
Potential Energy
Energy stored in an object due to its position or configuration within a field of forces.
Watt
Unit of power representing the transfer or consumption of one joule of energy per every second of time.
Explore the exciting STEM world with our free, online, simulations and accompanying companion courses! With them you’ll be able to experience and learn hands-on. Take this opportunity to immerse yourself in virtual experiences while advancing your education – awaken your scientific curiosity and discover all that the STEM world has to offer!
Energy simulations
Conservation of Mechanical Energy in a Roller Coaster
This simulation shows a motorless roller coaster: when the car is raised to its highest point, potential energy builds up, and as it descends, that energy is converted into kinetic energy. As the car goes up and down, the sum of its potential and kinetic energy remains almost constant, dynamically illustrating the principle of energy conservation and the transformation between mechanical forms. In real-world systems, friction and air resistance reduce the total energy, but this model clearly shows the ideal behavior in an isolated system.
Energy skate park I
This simulation allows you to explore how a skater moves on an ice track with curves and slopes, visually illustrating the changes between kinetic and potential energy. By adjusting the initial height, the shape of the track, or adding friction, you can observe how energy is transformed from one form to another and how the sum of both remains constant when the system is isolated. It is an excellent tool for understanding the law of conservation of energy in a dynamic and accessible context. Learn about energy conservation with a skateboarder!
Giants of science
“If I have seen further, it is by standing on the shoulders of giants”
Isaac Newton
Isaac Newton
–
Gaspard-Gustave de Coriolis
–
Become a giant
Mechanics, Part 2
Mechanics, Part 1
Dynamics and Control
AP® Physics 1: Challenging Concepts
AP® Physics 1 – Part 1: Linear Motion
AP® Physics 1
The Basics of Transport Phenomena
Professional development for Educators
Teach kids computing: Programming
Teaching Computational Thinking
Higher education assessing in the age of AI
Teach kids computing: Computing systems and networks
Giants of science
“If I have seen further, it is by standing on the shoulders of giants”
Isaac Newton
William Rowan Hamilton
–
Archimedes
–
Become a giant
Mechanics, Part 2
Mechanics, Part 1
Dynamics and Control
Circuits for Beginners
AP® Physics 1 – Part 1: Linear Motion
AP® Physics 1: Challenging Concepts
AP® Physics 1
Professional development for Educators
Advancing Learning Through Evidence-Based STEM Teaching
Teach teens computing: Cybersecurity
Teach teens computing: Data representation
Teaching Science and Engineering
Test your knowledge
How is energy defined in physics, and why is this concept essential for describing natural processes?
What is the relationship between energy, work, and force, and how does this connection help us understand the behavior of physical systems?
Why do we say that energy “cannot be created or destroyed”? Does it really never disappear?
What happens if an object gains energy? Does it make sense that this changes its behavior?
How come energy can be “stored” in an object if it’s not something we can see?
You may also be interested
Last simulations
To learn and experience
Take your knowledge to the next level with science kits and hands-on tools that connect theory with experimentation
Roller coaster

Teachers essentials
Notion
Organize your notes, tasks, and projects in one place. Notion combines notes, lists, and calendars in one flexible space.
Canva
Design presentations, diagrams, and infographics with easy-to-use templates and professional results
Genially
Create interactive content, presentations, and educational games in a simple and visual way
Desmos
The most intuitive graphing calculator to explore mathematics and create dynamic classroom activities
Tinkercad
Design in 3D and simulate electronic circuits for free; it’s the perfect tool for simple robotics projects
Your Infinite Library
Enjoy the freedom to explore millions of titles and a curated selection of magazines on any device
Join Prime for students and young adults
The best series. Millions of songs. All included with your subscription.
Science made fun
Learn with the best courses
edX
Online courses from leading universities and companies. Learn practical skills and earn professional certifications
Coursera
Courses from leading universities and companies. Learn practical skills and earn professional certifications
Udemy
Thousands of online courses tailored to your level. Learn at your own pace with expert instructors


