What is energy and is heat just kinetic energy?

[repugno]

What exactly is energy? Also, is heat just an effect caused by particles having a lot of kinetic energy?

 

[FZ+]

Yep. Heat is simply kinetic energy.

What is energy, though? I think Energy is a number, a value we can calculate for a certain situations, that we can use in certain calculations.

 

[pallidin]

Energy, as such, is always relative to its application or potential for use in an application.
A candy bar will impart energy to a normal human because we are designed by nature to use sugars as chemical energy. The same candy bar fed into a jet engine would be useless if not disasterous.
The applications ability to utilize a specific source(whatever it might be, from food to photons)is what determines the attribute of calling it "energy"
With energy being the ability to do "work", what is energy for one set of circumstances is not the same for another. So, energy is a concept, a bilateral concept at that.
For example, let's say that physicists in the year 3000 produced a new element, say element 400. Let's further say that the element emitted enormous quantaties of neutrons and minor amounts of other particles. If there were no use for those emitted neutrons than the physicists might say "well, element 400 is curious but of no use"
In the year 3500, physicists discover a way to use those neutrons from element 400 to produce vasts amounts of electricity.
With that, element 400 is then considered an energy source.
Again, "energy" is wholly relative to application.
Just some thoughts, feel free to correct.

 

[turin]

Energy is not quite arbitrary. It causes a divergence in space-time curvature to an extent that depends on the amount of energy. So, you can't just transform the energy away into nothing (because it must still cause the divergence).

 

[pmb_phy]

Originally posted by repugno
What exactly is energy? Also, is heat just an effect caused by particles having a lot of kinetic energy?

Nobody really knows what energy is. For details on what I mean by that please see

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

That said - there are various forms of energy which is well-defined. mass-energy is one form. And it can be shown that if momentum is conserved then so is mass-energy. Mass energy, T, is defined as the sum of kinetic energy + rest energy and has the value

T = m₀c²/sqrt{1-(v/c)²}

It can also be shown that total energy, E = T + V, is also conserved where V = potential energy. That is really the essence of what energy is. One of its assumed properties is that its (locally) conserved.