Like, i know it’s the ability to do work and all that, but this isn’t what energy is, it’s what energy does. What IS energy tho?
In: Physics
>Like, i know it’s the ability to do work and all that, but this isn’t what energy is, it’s what energy does.
No, it’s definitely what it **is.**
If it helps, think of it as if it were mana in video games. Everything has it, and to do anything requires spending mana. Just imagine any action or process that a system can perform is a spell that consumes mana. And to get more of it, it needs to be recharged by taking the mana of something else.
All matter around us is made up of massive atoms. The mass of a body represents its internal energy, which is expressed by the famous expression E = mc² discovered by Albert Einstein (c being the speed of light).
At its most basic level energy is the capacity to cause motion.
Chemical energy can move your car. Thermal energy is the kinetic energy of the molecules in an object. Gravitational energy is when something moves towards another massive object.
There are deeper explanations, but if you aren’t going to learn calculus you should probably ignore them. Somebody without a very strong math background isn’t going to comprehend Noether and symmetries.
Might be dumb but, WHY is energy there? Can’t two atoms interacting, just go and collide with each other rather than interacting with their energy shells?
All these scientific observations and experiments require words, the mind, and sense organs to explain what they do from the perspective of humans. The thing is, humans are using tools that are limited in their capacity to know what things are. It’s not their nature to know. We can talk about what they do, how they look, but not what they are. This is just the nature of these tools.
#Not ELI5, but…
Like you said… it’s a quantity describing how much work a system is capable of producing. Work is a “rate” quantity defined as an amount of energy being used up per second. That’s black and white definitions of things.
In practice you care about the “work” quantity a lot more often because you are usually trying to design something that can output “energy” *at a specific rate.*
Energy, then, **is just a quantitative property that can describe the state of an object or system.** A red hot piece of iron has high (thermal) energy State. A bullet speeding through the air has high (kinetic) energy state. An anvil sitting atop a 500-meter tall cliff has a high (gravitational potential) energy state.
If that anvil gets kicked off the cliff it will begin LOSING (potential) energy while instantly GAINING that exact amount of energy in another form (kinetic AND thermal due to air drag). This re-balancing of energy will continue until the anvil hits the lowest ground it can reach (or hits a coyote), at which point it is said to have 0 potential energy. The instant before impact, the anvil would have maximum kinetic energy and minimum potential, as it reaches top speed before a quick stop.
The re-balancing is known as “conservation of energy” and follows what we observe in real life. Energy is always conserved. The anvil started with a high state of potential energy and it ends with a high state of potential energy, even if we can’t see it. The air drag heated up the anvil slightly during its travel. Sound waves were emitted as the anvil falls through the medium of air. All the potential energy was replaced by kinetic during free-fall. Once it has landed, gravity still acts on it. If we could create a new deeper cliff, the anvil would fall some more. What this means is that **in the long term, objects and systems tend to exist in discrete states of energy.** The anvil can EITHER be on the cliff OR at ground level. So there are two possible energy states for that system.
It should be no surprise that the physics of electromagnetism are very similar. 12V car battery has a 12V “potential difference.” That means a single electric charge within the battery “feels” 12V of “force” pulling it towards the direction of opposite charge. This is analogous to how the anvil “feels” the potential energy of gravity pulling it off the cliff from high energy to lower energy. It’s pure luck, our previous understanding, and the beauty of nature to thank for this striking resemblance between Newtonian mechanics and electromagnetism.
It might help to imagine energy as a “system property” where you are given a bar graph of the various types of energy we know of like grav potential, kinetic, thermal, acoustic, electric potential, etc. When the system is dormant, everything is FIXED and the bars each show a different value. When we force the system to accept or perform work… aka the system undergoes an event…the energy levels will change by type. At the end of the event, the system will have the EXACT SAME amount of energy, just distributed to the categories a bit differently.
Now, you might think giving off heat and sound would be a net energy loss, thus breaking the rules. That just means you haven’t properly considered the system at hand, which includes the atmosphere that the sound and heat has dissolved into. When the “system” is properly selected, we can take advantage of the “conservation rule” and know for a fact that the net CHANGE in energy will be 0. This can help us safely assume things we otherwise couldn’t measure or know about.
In practical matters, if you know the mass of a bullet as well as the mass AND speed of the gun’s recoil. You could determine the bullet speed as it leaves the barrel. This is one example where energy methods can help out a lot with something that would be tough to measure or calculate.
energy is kind of counterintuitive because it is less something that makes things happen and more a way to describe what is happening.
So we see an object move from a to b, we say „the object apparently had more energy in place a, so it moved to place b to reduce the energy“ Now what this means is basically „seems like the object had a reason to move, so it moved.“ it‘s as general as possible.
like when something falls down. It used to be high, it wasn‘t lying ontop of anything, so it fell to the ground. The reason, as we know, is gravity. But maybe if we don‘t know the reason or if the reason is too complicated and unimportant, we might want to just say „there was pontential to move, and then it moved“.
It sounds weird when you describe everyday phenomena like that but basically everything has an energy level that is influenced by everything around it.
You have a child, the child has two friends and he wants to visit one of them. Friend 1 has an annoying little brother while friend 2 has strict parents who don‘t let their kids watch tv. Say, for the kid the annoying brother is worse than a lack of tv. So based on this, we can give the houses an inherent attractiveness score. The home has a low level of attractiveness, house 1 has a higher score but house 2 has the highest score (energy is inverted for math reasons, so high score means low energy). we can play with that by giving family 1 candy for the kids or buying an x-box for the home. This alters the scores but it‘s always low score => high score.
The attractiveness score isn‘t necessarily something physical but it definitely exists as a property of the houses. Our child has desires and free will, but technically we don‘t have to know that to determine the attractiveness score. we just have to watch the child long enough and figure out all relevant parameters. And this is how we determine the energy levels of things in relation to other things. Molecules might not have a conscious desire to move and bind and split, but they do so all the same. And we can give each possible state an energy level, that reflects how it‘s gonna behave and then we can do a whole lot of math with that.
Energy is a bit hard to define.
For example: in hot air, the “energy” it has when you warm it is the average kinetic energy of its atoms increasing. So in that case its kinetic.
A photon has energy – but its a different thing than the kinetic energy carried on the speed of an atom.
Potential energy is converted to kinetic and vice versa, but its different things.
The energy available in an unbroken uranium 235 atom is something else entirely, but then it converts to stuff moving very fast and radiation.
I’d say that its a value that aggregates several different things giving some equivalences
Here’s a slightly mind blowing follow up question: what’s the origin of mass? You’ll find it surprising that somehow mass and energy are deeply related.
Energy is ultimately just a human concept. It is not a true physical property. In science its like the ability for something to do damage or do work. Fast moving things have more energy than stationary things, combustible things have lots of energy to release, heavy things that can fall have more potential energy than lighter things because they can do more damage.
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