What is Energy?

Energy is the most powerful and useful concept in all of physics, but what exactly is it?

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Kronos: Devourer of Worlds

Written and Hosted by Matt O'Dowd
Produced by Rusty Ward
Graphics by Matthew Ranker
Assistant Editing and Sound Design by Mike Petrow and Meah Denee Barrington

In physics energy is not a substance, nor is it mystical. Energy is a number. A quantity. And the quantity itself isn’t even particularly fundamental. Instead, it’s a mathematical relationship between other, more fundamental quantities. It was 17th century polymath Gottfried Leibnitz who first figured out the mathematical form of what we call kinetic energy – the energy of motion. He realized that the sum of mass times velocity squared for a system of particles bouncing around on a flat surface is always conserved, assuming no friction and perfect bounciness. Leibnitz called this early incarnation of energy vis viva – the living force.

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[astrowuff]

No energy was lost or harmed in the making of this video

[ekaramdani]

"a physicist sees a guy standing in the rooftop and shout don't do it you have so much potential"

For whatever reason i instantly laugh so hard

[problemecium]

At least Space Time is here for me on Valentine's Day.

[xunxekri]

0:06 I died.




Like, collapsed onto the floor.
My heart stopped beating.
That was amazing.

[xtreme]

They couldn't have picked a better person to deliver the content on this channel. Matt has the most relaxing voice, anybody else put on space time before bed? I love the content of the videos, but inversely I can also just listen and let it lull me to sleep without fail. Growing up is weird 😜

[Sonicboum]

"Mom, i'm not doing anything, i'm just conserving my potential."

[RallyCarDelta]

What a cliffhanger! My guess is that it has something to do with spacetime and how energy is a representation of that effect. Next thing you know, Matt will tell us energy isn't real and it's only an artifact of our limited perception of our reality. I'm grasping at straws here. I can't wait for the next one. Best channel on YouTube Matt. Keep up the amazing work.

[massimilianoc]

An amazing summary of key milestones of last 300 years of physics. Man, you know physics and no doubt you master how to teach it! Thanks.

[TheWyrdSmythe]

“Don’t jump; you have so much potential!” I’m still laughing! 😂

[anywallsocket]

This could've gone into Gauge Symmetry, which would've been VERY interesting - albeit difficult to explain accessibly, but if anyone can pull it off it's PBS SpaceTime!

[yugchauhan]

Hey matt i am an 11th grade student but due to pbs spacetime and infinite series and some other channels made me develop intrest for quantum mechanics.

Now i have finished 'Introduction to quantum mechanics by david griffith'. Thanks🖒🖒
Ps:- I am a Biology student and giving NEET in 2020

[Spectacurl]

At the 7 minutes mark I was like "This video could be named The Essence of Langrangian, Hamiltonian and Statistical Mechanics" then I had a nerdrgasm. I love this channel so bad!

[kataseiko]

You seem to have skipped the part that explains "what is energy?".. However, it appears that nobody can exactly define what it is. Leibnitz and some others defined it as "the potential to do work". I have not seen or heard any better definition yet.

[MClaudeW]

Man... you know, this video has special relevance to me. In high school I remember learning about potential kinetic energy and being convinced that it couldn't be right and was just a tool for math. I went on to learn about space curvature and felt vindicated enough but still curious. Here you introduce concepts that both make it workable in my mind and motivate me to learn what it is in Einstein's work that made me so sure upon hearing it. Too bad I suck at math.

[DallyDragon]

"Lithium is grunge, not metal" That's the best thing I have heard all day!

[cloudpoint]

Physicist Richard Feynman’s thoughts on Energy:

“There is a fact, or if you wish, a law governing all natural phenomena that are known to date. There is no known exception to this law – it is exact so far as we know. The law is called the conservation of energy. It states that there is a certain quantity, which we call “energy, ” that does not change in the manifold changes that nature undergoes. That is a most abstract idea, because it is a mathematical principle; it says there is a numerical quantity which does not change when something happens. It is not a description of a mechanism, or anything concrete; it is a strange fact that when we calculate some number and when we finish watching nature go through her tricks and calculate the number again, it is the same. (Something like a bishop on a red square, and after a number of moves – details unknown – it is still on some red square. It is a law of this nature.)
…
It is important to realize that in physics today, we have no knowledge of what energy ‘is’. We do not have a picture that energy comes in little blobs of a definite amount. It is not that way. It is an abstract thing in that it does not tell us the mechanism or the reason for the various formulas.”

[cosmic_gate]

When I binged your channel I didn't pay attention to the fact that videos were released only weekly. The last week has been too long. Finally a video!

[lindy]

So... what's energy?
You seem to have skipped that part.

[riazabdulla]

I teach AP Physics 1, and this is such a great supplement to the work that we do in class. I teach some very curious students who will definitely appreciate this.

[KungFuBlitzKrieg]

The way he holds his hands makes me want a Hershey's Kiss.