# What is energy

1. ### Ghetalion

21

Is energy simply kinetic interactions between matter BY matter? My understanding is that chemical and heat are both electromagnetic and are simply photonic flux.

2. ### Locrian

1,844
It's a scalar quantity associated with the state of a system. That's a pretty vague definition, but since we're in the QM forum, I think it's appropriate.

3. ### Ghetalion

21
A state of a system

Meaning the position of matter within that system, correct?

4. ### Antiphon

There's more to it than position. But since this is a QM forum,
energy numerically defines the frequency of something.
We don't know know what that something actually is but mathematically
it looks like this:

$$\Psi = e^{i\frac{E}{\hbar}t}$$

5. ### Ghetalion

21
Frequency suggests a fluxuation of material density... doesn't it?

6. ### pmb_phy

Nobody knows what energy is.

Pete

147
8. ### HallsofIvy

40,784
Staff Emeritus
"Energy" is a book-keeping device. It was noted pretty early on in physics that in simple collisions, two quantities mass*velocity and 1/2 * mass* velocity2 stayed the same which made them easy to use- one was called "momentum" and the other "kinetic energy". It was observed that the speed of an object (and so it's kinetic energy) increased as it fell, decreased as it went up. "Potential energy" was defined in order to keep "total energy" constant. Of course, if you added friction, you no longer had conservation of those energies but could observe that the temperature increased proportional to the lost energy. Okay, "heat energy" keeps the book keeping straight! As of the advent of relativity, because "e= mc2", we had to include mass itself as a kind of energy!

9. ### pmb_phy

Nice post HallsofIvy. You are probably aware of this but that does not define energy. It only defines a property of energy. You'll note that total momentum also satisfies the property you just described.

I took a crack at this topic here

http://www.geocities.com/physics_world/mech/what_is_energy.htm

Pete

Last edited: Aug 20, 2005
10. ### Joethemonkey

2
first of all i'd like to point out that heat is not electromagnetic, Microwave is electromagnetic.. Heat is the vibration of particles in a substance...

secondly....... its late and i am too tired to finish this post.... *laught out loud* hopefully i'll remember to add another concluding post later... Goodnight

11. ### Joethemonkey

2
oh by the way i mentioned microwave,. because it transfers into heat energy ... *Microwave* ovens use microwaves to heat up food... check out some articles on "howstuffworks.com" that website has some real good information on electromagnetic waves.. light and radio,. energy... a great information source for this kind of thing... Hopefully HowStuffWorks will be able to answer your question,. as i am too lazy and tired right now

12. ### DaTario

564
I would put it like this:

Energy is a class of mathematical combinations of quantitative aspects of one system and its enviroment which forms a way to compute the maximum work that can be done by this system on the parts of its enviroment.

Best Regards

DaTario

13. ### Masoud

3
In my opinion, the best definition of energy would be embedded within M-Theory.

Masoud Zargar

14. ### DaTario

564
Could you please write this best definition of M-theory ?

Best Regards

DaTario

15. ### Telos

147
Maybe we should ask the Department of Energy?

16. ### Zelos

76
im getting sick of this question. ppl ask what energy/matter/charge is. this are proepties matter and things have. its not like its particles that sourond other particles

17. ### Telos

147
Well, Zelos, this is a little different. There isn't a Department of Matter or a Department of Charge.

19. ### Telos

147
And there's a State Department. Can't tell if it obeys Pauli Exclusion, though. They all look the same.

20. ### mcah5

40
According to Feymann, energy is just a book-keeping device with the very useful property that energy is conserved. The conservation of energy comes from the fact that experiments are time symmetric (aka "things do not depend on the absolute time.)

Edit: I can't spell Feynman