system
Given the following post, respond as if you're commenting on Reddit:
human
What is energy?

I've heard that matter and energy are convertable. But I find my understanding of what energy is to be lacking. In my understanding, it's vibrating matter.

What happens to matter when it converts to energy? Do sub-atomic particles "evaporate", if you will, into a burst of photons, absorbed into whatever they collide with, imparting energy?

So to illustrate, when fission occurs, as in a nuclear weapon, is matter permenantly lost because it's been converted to energy? If you could go around and collect all the matter that was the core of that bomb, now nuclear fallout and lighter elements, would there be less mass?

I imagine I'm close, but I could really stand a clarification.
gpt
No, it's not vibrating matter.

Energy is a property of a physical system. Just like an object can have a speed, or a mass, or a height, it can also have an energy. But it cannot _be_ energy, just like an object cannot _be_ speed.

There are different types of energy. Each type is related to some other physical property. For example, an object has an amount of kinetic energy that depends on how fast it's moving. It has an amount of gravitational potential energy that depends on how far away it is from the Earth (and other objects). It has an amount of mass energy that depends on its mass (which is a "built-in" property of some fundamental particles).

It's inaccurate to say that matter converts to energy. You wouldn't say that matter converts to speed, after all. For nuclear fission, for example, all that happens is that some particles break apart. In some other types of interactions, one type of particle turns into another. Either way, you can have changes in how the energy is distributed - for example, a system (like an atom plus a neutron) might start out with a certain amount of energy, mostly mass energy but a little bit of kinetic energy, and end up with less mass energy but more kinetic energy. The total amount of energy stays the same, though. (Except in some very exotic scenarios.)