The Meaning of Energy? Core Physics Principle Explained by Parth G

Energy is an extremely important concept in all of physics. It is used everywhere to describe how different systems will behave. But what exactly is energy in the first place? What is the meaning of energy?

This difficult-to-answer question can be thought of in terms of a few different explanations. The one I prefer is that energy is a mathematical concept used to describe how different systems behave and phenomena occur. We can think of it as a mathematical quantity that we assign to anything relevant in what we are studying. Then, energy transfers (i.e. from one form to another, or from one place to another) occur in such a way that they obey the Law of Conservation of Energy. This allows us to predict how our system will behave over time.

Although we are talking about assigning energy values to different parts of our system, this does not mean we can randomly assign any energy values. These energy values are carefully calculated to be consistent with how everything around us seems to behave. An object with a specific mass moving at a certain speed, for example, will have a very specific value of kinetic energy based on its mass and speed.

Based on all experiments we've done so far, the Law of Conservation of Energy seems to hold extremely well. Therefore, we can use it to make predictions about energy transfers in our system, as well as how these will affect different parts of our system. And it's very interesting that the system can be very tiny, or it can be as large as our whole universe.

Another way to think about energy is that it is a physical property that objects have. For example, a moving car HAS kinetic energy (rather than the energy being a mathematically assigned quantity). This is a perfectly reasonable way to look at it, but if left unclear it can lead to some misconceptions. For example, it is easy to think based on this description that energy is some "stuff" that can flow from one object to another, almost like a fluid. And indeed, a long time ago scientists thought of heat (a form of energy flow) as a fluid. However energy itself is not a fluid, and does not have form in and of itself, like other "stuff" does. It can be thought of as "flowing" from one object to another, or transferring to a different type of energy (e.g. gravitational potential energy being transferred to kinetic energy as an object falls to Earth).

Finally, a common definition of energy is that it is the ability to do work (force x distance). But often, wordy definitions of work are stated in terms of energy. So this can lead to a circular argument, and if you are not fully comfortable with at least one of these terms then these definitions are of no help.

At the end of the day though, the reason the concept of energy is so useful is because of the conservation law. Energy cannot be created or destroyed, only transferred from one place to another, or from one type to another. It almost doesn't matter what energy is.

In this video, we also discuss how some forms of energy (e.g. potential energy) seem like a bit of a fudge to make the math work out. "Stored energy" that allows stuff to happen in the future, can easily seem like something's gone wrong. However this shows the problem with thinking about potential energy as "stored energy", or as "stuff". Additionally, all objects that we've ever studied so far seem to behave consistently with each other in terms of potential energy. The fact is, this energy value that we assign to objects exactly predicts how they will behave if a given amount of potential energy is lost - in all systems!

Some interesting reads (even though I don't agree with everything in them):

Many of you have asked about the stuff I use to make my videos, so I'm posting some affiliate links here! I make a small commission if you make a purchase through these links.

Thanks so much for watching - please do check out my socials here:
Instagram - @parthvlogs
Music Chanel - Parth G's Shenanigans

Timestamps:
0:00 - Energy: A Very Central Concept to Physics
0:35 - A Useful Mathematical Concept to Assign to the System, and Making Predictions With It
1:47 - Can We Assign Any Random Energy Value?
2:54 - The Law of Conservation of Energy: Constant Total Energy
4:16 - Energy as a Property vs. Energy as a Mathematical Concept
4:48 - Misconceptions of Energy as "Stuff"
5:36 - Potential Energy: A Fudge?
7:30 - Energy as the Ability to Do Work
8:20 - Overview

[girindrasinghrathore]

Parth's way of explaining concepts are always unique & different from others

[mazzky]

Thank you so much for this video! As a layperson this is one of those questions that never seems to get addressed. I don't think I've ever heard anyone say 'Its a mathematical concept'. This is the sort of explanation that helps me sleep better at night.

[kikivoorburg]

Thank you!! About a year ago I fell into a rabbit hole trying to figure out what “energy” actually meant, and the result I came to was exactly what you described: a circular definition based on “work”. At that point I gave up searching, but now I’ve finally gotten a clear answer!

Energy just being a mathematical concept which represents the consequences of the conservation of energy makes a lot of sense. It is just the best model we currently have to describe these particular object-to-object interactions. Whether or not it is a property (like mass) or something else is neither relevant to our understanding (yet?) nor known, which is why the definition ends up so confusing!

Your channel is by far the best physics channel I’ve ever come across. You explain the most complex topics in simple, understandable ways, keep it up!

[johnboze]

My high school electronics teach said it the right way "WATT IS POWER" Q and A in the same line!

[tehlaser]

The analogy that finally clicked with me is that energy is the currency the universe uses to balance its books (or that humans use to understand it, if you don't like to anthropomorphize). In the same way that money just sitting around may as well not exist, energy that isn't changing in some way doesn't matter. Both only have meaning when they can move. Energy and money are both useless numbers until they get transferred somewhere.

The equations for various forms of energy (motion, heat, chemical, rest mass, whatever) are like prices or exchange rates. They tell you how to convert the currency. And like accounting, the universe follows double-entry bookkeeping. For every debit there is always a matching credit. The currency might look different, but the value is always the same.

[ali-omuv]

You could shortly mention Noether's theorem and the fact that any conservation law is implied by a specific type of symmetry ?

[elaadt]

Great explanation for people with high school level physics at most. The concept of a number calculated and assigned to an object or system came across well.
However, why this number should be conserved remained a bit "fudgy". You could mention Noether's theorem as a teaser for another video. This would give the viewer a sense that there is some solid science behind conservation laws without going into details here as it is beyond the scope of this video.

[MuharremGorkem]

I would expect a compare & contrast of energy versus other "concepts" (such as momentum, elasticity, conductivity, etc.) so that one can make a clear distinction of concept of energy and others that we also assign to physical objects or the world as a whole. Momentum is of particular interest. They both are concepts and have a common play ground. So, if we have one, why do we need the other? Are they inter-related? Is there anything else (beside the momentum) that is closely related with energy? How does this concept differs in Newtonian, relativistic and quantum mechanical system? Are the differences essential or pragmatic (computational etc.)? What about chemical energy? How on earth a charged battery behaves so similarly to a stretched spring?
And the symmetries vs conservation laws... What is the symmetry that gives rise to conservation of energy?
What about an expanding universe and conservation of energy?
A very interesting aspect of energy is uncertainty principle expressed in terms of energy / time-interval... What does it tell us? Vacuum enrgy?

Note that I am just a guy who is interested in popular science expecting a little bit more on the topic.
I wish you try another take on the subject.
regards,

[adibgbs]

what i found verrry useful to me, is understanding why the hell do physicists talk about work?
why didnt they speak about energy, and that's all !
thank you parth

[LuisAldamiz]

Good technical explanation but I think that what is energy does matter when, after all, we are defining nearly everything in terms of energy (gravity and the quantum forces/particles/fields most notably). Shouldn't understanding what energy is be the natural path for the betterment of physics? Maybe even for finding the ToE?

[randomblueguy]

Any discussion of what energy is should include Neother’s theorem.

[thecoloroctet]

For me, the most intuitive definition of energy is the time component of the 4-momentum. It’s a more general/advanced definition, but I think it gives the intuition as to why both are constructed so similarly and both are conserved. Cheers!

[chrislong]

I'm late to this party but you've cleared up the one thing that has bugged me forever!
There is no clear definition of what energy is!
I've always wanted a clear definition but never found one. By simply acknowledging that in this video, I feel better and won't get hung up on something unnecessary and really trivial!
Thanks!

[prashantlale]

Wow! Really acknowledged with parth Thank you so much

[LQhristian]

Great explanation! However, this description on energy is focused primarily on mechanical energy/systems. The law of conservation of energy behooves us to seek its higher/highest source!

[michaeledwardharris]

Very nice. I appreciate you attention to interesting and subtle details. I'm addicted to your vids.

[bhavitarora]

Thank you so much for this. I'm preparing for JEE examination and just today I finished the work power energy chapter but still had doubts & this video cleared all of them

[suyashpurwar]

I loved it! I read this in Resnick Halliday too but it wasn't clearly explained there.

[BytebroUK]

I'm impressed - you did all that without even mentioning "mc^2"!

[malchicken]

I wondered while watching how energy relates to entropy. Is a higher entropy system the same amount of “energy” as a low entropy system? Or energy is also just a sort of “currency” to help with the accounting when changing from one state to another?