# What is energy?

1. ### Rutherford

10
Okay, so I've been reading about energy and no source seems to make it clear what energy really is. I understand how energy relates to objects in the real world like with moving objects and heated objects, but other forms of energy are more confusing.

Firstly, what is electrical energy? I know that electrical energy is carried in an electrical field, but what is it made of? I don't see how energy can be carried by something that isn't really real. Is it waves? If so, where do these waves come from, and where do these waves travel? If the electrical field stretches to infinity, then is the energy stored in an infinitely large place?

Also, in nuclear fission, where exactly does the energy come from? I get the whole thing about mass turning into energy, but what part of the atom turns to energy? When a neutron collides with an atom, the products have the same atomic mass as the reactants, so what mass is actually being turned into energy? It's clearly not the protons or neutrons, since those all remain with the fission products, so then is it the electrons being turned into energy?

2. ### ice109

energy is ability to do work

mass does not convert to energy, the energy in fission comes from the binding energy inside the nucleus, i'm pretty sure from the strong nuclear force but i could be talking out of my ass here.

3. ### Rutherford

10
So then what is the binding energy made of?

4. ### ice109

energy isn't a thing, it is a descriptive characteristic of a particle.

5. ### mgb_phys

8,809
It helps to think of energy as not real - it's just there to get the books to balance. Energy is just a concept to make it easier to describe how 'work' gets transferred.
In binding energy the particles really do weight less when in the nucleas - once the extra energy is radiated away.

Last edited: Jun 21, 2007
6. ### Rutherford

10
Okay, well, then I don't understand how work gets transfered from binding energy in an atom to heat... What happens there? Obviously, something moves from the atom to whatever is being heated, so what is being moved?

3,016
I am not a Chemist or a Physicist, so I am sure that someone can better explain this. But, as I would understand this is that the energy that binds an atom together is not made of anything; it is more like when a weight is held high above the ground, the kinetic, or moving, energy that could be created is a result of the weight's gravitational potential energy. An atom's energy, I believe, arises from the potential energy created by the binding of its subatomic particles.

I know this is a very shoddy explaination, but I am sure someone will correct and enlighten me.

~Casey

8. ### Dr. Proof

29
In mechanics, kinetic energy is the term given to the mathematical formula Fd=(1/2)mv^2. In everyday use, and even when people try to talk about technical things, the word "energy" gets tossed around extremely loosly. Focus on understanding the mathematical formulas by knowing how to derive them. Physics is not about obtaining some deep ultimate understanding. If you understand where the formulas come from, and if you know how to solve physics problems, then you understand physics.

9. ### ice109

what are you talking about? physics is exactly about getting a deep understanding of the way the world works. you come to understand the mathematical formulas by understanding the physical process. if you only know how to solve physics problems you don't know anything.

10. ### Rutherford

10
Yes... Personally, I don't really care about solving physics problems out of some book. That seems to be what modern day physics has become. I'd like to understand what the physicists have come up with. From what I'm gathering, there is a lack of understanding as to how physics (namely energy) actually works, and I'm trying to solve that problem starting with myself.

I'm fine with an answer of "we don't know what energy is." If that's as far as physics has come, then I'm alright with that. However, I am having trouble believing that's the answer.

What I'm concerned with, I guess, is how does energy work? Like how does that electric field perform work? And how does the splitting of an atom create heat? I just want to know where this stuff is coming from.

11. ### ice109

physics has not become "problem solving", physics what it has always been; explaining phenomena, answering the why.

dude i can sympathize with you but you're asking questions about extremely abstruse things and i get the impression you only have a basic understanding. start from the bottom and work your way to the top, use this curiousity to drive you but don't expect to understand something extremely complex before being able to.

12. ### Dr. Proof

29
Physics is an experimental subject. In physics, one can only understand things experimentally. How do you know that objects fall towards the earth? you would have no reason to believe such a thing unless you saw it for yourself. Physics is not about getting a "deep understanding" as you have said; Physics is about getting a fundamental understanding. For example, objects that fall towards the earth create a study in and of themselves. You can mathematically describe falling objects and predict the specifics of their motion without having a "deep understanding" of "why" the objects fall towards the earth. Now, Newton's universal law of gravitation helps in mathematically explaining falling objects further; however, Newton's universal law of gravitation does not explain "why" masses exert forces on one another. You see, whenever you ask the question "why", you will never get an ultimate answer, you will always be able to ask "why" one more time. So you see, physicists try to understand things "fundamentally", not "deeply".

13. ### ZapperZ

30,731
Staff Emeritus
OK, this may sound highly irrelevant to you, but try to answer this one:

What is an apple?

No, really, try it!

If you do, you will discover for yourself that in answering the question, what you end up doing is listing all the PROPERTIES AND BEHAVIOR of what you define to be an "apple". You will realize that when you ask "what is so-and-so", the ONLY thing that makes any sense is to describe a series of characteristics that are associated with that object in question.

Try it with "electrons", "pumpkins", "my sister", etc...

Now, the same can be said about "energy". The reason why you seem to think it is "ambiguous" is because out of the MANY characteristics of energy, some of them are used in particular situations, while others are used in other situations. However, the other difficulties also is that you appears to have understood only the basic, intro level physics. This is not a criticism. However, because of that, you must also realize that you have BARELY seen the whole picture of how we deal with "energy". For example, you would not have come across the Lagrangian/Hamiltonian mechanics in which there are only TWO forms of energy that really matters in describing the dynamics of any system - kinetic and potential energy of the system. That's it. So one can, in principle, simply answer your question as to what is energy as "kinetic and potential energy", and that's that. In fact, for quantum mechanics, the Hamiltonian of a system consists of just those two terms!

So your "binding energy" for example, gets lumped into the potential term, while any energy of motion such as electricity, would be in the kinetic term. Any EM interaction could either be described via the vector potential, or via operators if we decide to use quantum field theory.

Certainly, there are profound description of what energy is. However, you must also be reasonable on your part to accept that, unless one is willing to put a lot of effort into really studying it, at some point, all that the rest of us can do is simply TELL you that this is so. You are certainly more than welcome to check this yourself by studying up on more advanced topics.

This question gets asked very often, and I think a good search on such a thing will come up with many threads that have already addressed this issue.

Zz.

14. ### Rutherford

10
I would argue that the question of "What is energy?" is about as basic as it gets right after "What is physics?" Just because it's not explained at the basic level in physics text books does not mean that it is not a basic question.
Okay, comparing my question to the apple question, I would want to know that an apple is made of proteins, glucose, lipids, whatever it's made of. That's what I'm asking about energy. That's the one specific property that I'm trying to single out. What is it made of?

Last edited: Jun 21, 2007
15. ### ice109

you're arguing semantics. lots of physical theories explain why things happen and not just how. newton's law of gravitation explains why in the sense that he believed it was axiomatic that masses exterted a gravitational force on each other, and not just how an object travels when it is influenced by gravity. now we're at a point where the constituent particles are the why, if there is something smaller than them and different physics there we will find it and answer the why processes happen question.

16. ### ice109

dude read the tractatus by ludwig wittgenstein, your questions are meaningless and that's not a criticism either but they simply have no meaning. zapper makes a very good analogy.

17. ### ZapperZ

30,731
Staff Emeritus
But requiring that all "What is...." must consist of the CONSTITUENTS of the subject doesn't make sense all the time. For example, I could ask "what is the color red?". Do you then describe what "red" is made of? What about "what is time?". This is the same type of question we had before when someone asked for the size of a photon. It is a strange question when a photon was never defined as a regular particle with a definite physical boundary in the first place. That's like asking how heavy is purple.

Do people ask about Force is made of? What about speed or acceleration? Is it made of anything? A "What is... "question need not have the constituents of the object in question as the answer. If you always require that, you'll see many instances where you're asking for absurd answers.

Zz.

18. ### ice109

isn't force made of mediating particles?

19. ### ZapperZ

30,731
Staff Emeritus
Not the classical force. Furthermore, a force isn't MADE up of those particles. When you start talking about those force carriers, then you are using the quantum field theory, in which not only the classical field doesn't exist, but the concept of "force" also do not exist. Force, in fact, is replaced by the exchange of these particles. So no, it isn't made up of these particles, but rather the concept has been REPLACED by these particles.

Zz.

20. ### ice109

yea i knew that statement was nonsensical