# What Actually Is Energy?

• AJ_2010
In summary: Sorry.In summary, energy is conserved by virtue of the laws of physics, and has a relationship to momentum and time.
AJ_2010
Hello guys, newbie here.

Just a question about 'energy' which may or may not have an easy answer.

As we all know 'energy' is the potential of a physical system to do 'work'. And 'energy' can be converted from one form to another as per the relevant laws.

But what actually is 'energy'?
Or what actually is this 'potential to do work' stuff made of?

As we also all know, 'energy' is mass x speed of light squared.

So is it right to assume that 'energy' has a direct connection to light speed? And if so is 'energy' constrained by the value of light speed in any way? (In that light speed is a single value in a vacuum and a single value in other mediums etc.).

Am I getting mixed up in various meanings or are these valid questions?

Thanks for any help on this.

"energy" is that quantity which is conserved by virtue of the laws of physics not changing over time.

Hi AJ_2010, welcome to PF

AJ_2010 said:
As we all know 'energy' is the potential of a physical system to do 'work'. And 'energy' can be converted from one form to another as per the relevant laws.

But what actually is 'energy'?
Or what actually is this 'potential to do work' stuff made of?
In physics we often define some quantity. Once you have defined a quantity that definition is what it is. There is rarely any scientific answer to questions about what something "actually" or "really" is independent of the definition.

However, what is often interesting and useful for gaining a deeper understanding of something is to learn its relationships with other quantities. For instance, as JDlugosz mentioned, energy is related to the symmetry of a system, specifically the fact that energy is conserved implies that the laws of physics don't change over time.

Another interesting relationship is the relationship between energy and momentum in relativity. They have the same relationship to each other as time and space have, so the conservation of energy and the conservation of momentum can be combined into one unified conservation law.

Thanks for the replies.
Seems I was trying to find an explanation of something that doesn't have the type of explanation I was looking for.

Hello there, welcome to the scientific community! Your questions about energy are very valid and it's great that you are seeking to understand this concept better. As you mentioned, energy is defined as the potential of a physical system to do work, and it can exist in various forms such as kinetic, potential, thermal, and electromagnetic. The concept of energy is fundamental to understanding the behavior and interactions of matter and is a key concept in physics.

To answer your question about what energy is made of, it is important to note that energy itself is not a physical substance. It is a property or characteristic of matter and is measured in units such as joules or calories. In other words, energy is not a tangible thing that you can hold or see, but rather a description of how matter behaves and changes.

The equation E=mc^2, which you mentioned, is a famous equation proposed by Albert Einstein that relates mass and energy. It states that energy is equal to mass multiplied by the speed of light squared. This equation shows that mass and energy are essentially interchangeable and can be converted from one form to another. However, it does not mean that energy is directly connected to the speed of light. The speed of light is simply a constant that appears in this equation and has no direct influence on the value of energy.

In terms of your question about whether energy is constrained by the value of the speed of light, the answer is yes and no. The speed of light is a constant in a vacuum, meaning that it is the same no matter where you measure it in space. However, in different mediums such as air or water, the speed of light can be different. This does not necessarily constrain energy, but it does affect how energy is transmitted and absorbed in these mediums.

I hope this helps clarify some of your questions about energy. It is a complex concept, but with further study and exploration, you will gain a deeper understanding of it. Keep asking questions and seeking knowledge, that's what being a scientist is all about!

## 1. What is the definition of 'energy'?

Energy is defined as the ability to do work or cause change. It exists in various forms such as kinetic, potential, thermal, and electromagnetic energy.

## 2. How is energy measured?

Energy is measured in joules (J) or calories (cal). It can also be measured in other units such as kilowatt-hours (kWh) in the context of electricity.

## 3. What are the different types of energy?

There are several types of energy, including kinetic energy (energy of motion), potential energy (energy of position), thermal energy (energy from heat), chemical energy (energy stored in chemical bonds), and electromagnetic energy (energy from light).

## 4. How does energy transfer from one form to another?

Energy can be transferred from one form to another through various processes such as conversion, transformation, and transfer. For example, potential energy can be converted to kinetic energy when an object falls, and thermal energy can be transformed into electrical energy in a power plant.

## 5. What is the role of energy in our daily lives?

Energy plays a crucial role in our daily lives, as it is required for almost all activities we do. From powering our homes and transportation to providing us with food and communication, energy is essential for our survival and the functioning of society.

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