Kinetic Energy EXPLAINED in 5 Levels - Beginner to Advanced (Classical Physics by Parth G)

What is kinetic energy? How does it depend on the mass and speed of an object? And how do relativity and quantum mechanics deal with it? We'll answer all of these questions in this video, in 5 levels of difficulty.

Level 1 - Kinetic energy is the energy that an object has when it is moving. The faster it moves, the more kinetic energy it has. Energy is a quantity or number that we can assign to different parts of whatever we are studying, in order to predict how it should behave at some point in the future (based on Conservation of Energy). Kinetic energy (just like other forms of energy) is measured in Joules.

Level 2 - The formula for kinetic energy is (1/2)mv^2 where m is the mass of our object, and v is its speed. So we find that if we double an object's speed, its kinetic energy increases fourfold. If we double the mass of the object, its kinetic energy increases twofold. It's worth noting that v refers to the speed of the object, not the velocity. In other words, kinetic energy is a scalar.

Level 3 - We've mentioned the speed of an object multiple times here... but what is this speed measured relative to? Whenever we measure the speed of an object, this means the object is moving a certain distance away from some reference point, in every unit of time. From different reference frames, an object may be moving at different speeds. Therefore, these different frames may decide the object has different amounts of kinetic energy. Which is correct? The answer is all of them! Reference frames do not need to agree on how much kinetic energy an object has. As long as the total energy in each frame is conserved, that's all that matters. So to one observer an object may have no kinetic energy, while to another the same object may have kinetic energy... and this is ok!

Level 4 - In special relativity, every object has a certain amount of energy, even when at rest relative to the observer. This energy is given by the famous equation E = mc^2. However when the object is moving, the energy-mass-momentum equivalence equation (a much more complicated one) takes effect. In this video we discuss one of the basic assumptions in special relativity, that the speed of light is constant for all observers. We then also see that the kinetic energy of an object in any reference frame, is the energy it has while moving, minus the energy it had when it was stationary. Upon using a binomial expansion for small velocities, we see that the main (biggest) term of the relativistic kinetic energy equation is the same as the classical, Newtonian kinetic energy equation! However in relativity there are infinitely many terms getting smaller and smaller.

Level 5 - We've only talked about linear kinetic energy so far. We can also consider the rotational kinetic energy of an object when it is undergoing some sort of angular motion. The rotational kinetic energy depends on the angular speed of our object, and on its moment of inertia. The angular speed is simply how much angle is covered by our object per unit time. And the moment of inertia is the equivalent of mass for angular motion. Just like mass is a measure of how hard it is to move an object in a straight line, the moment of inertia is a measure of how hard it is to move it in an angular manner. The moment of inertia depends on both the mass of the object, as well as its shape.

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Timestamps:
0:00 - Intro: Kinetic Energy by Parth G
0:31 - Level 1 - What is Kinetic Energy? How do we measure it?
1:37 - Level 2 - The Formula for Kinetic Energy EXPLAINED
3:54 - Level 3 - Kinetic Energy in different Reference Frames!
5:52 - Level 4 - How does Special Relativity deal with Kinetic Energy?
9:54 - Level 5 - Rotational Kinetic Energy, and Quantum Mechanics
12:17 - Thanks for Watching! Please Subscribe for more Fun Physics!

[ParthGChannel]

And as always, let me know what topics you'd like me to cover in future videos :)

[amshumansharma]

keep up the good work homey and yes totally would like more of 5 level vids

[MaxxTosh]

I’d kinda like “five levels of math used in physics”
Could go down basic arithmetic, trigonometry, basic calculus, vector calculus, then higher level maths that are way beyond me

[sadikmahmud]

I would very much like 5 levels of voltage.That shit's crazy

[TheWalkingSteakhouse]

It's actually insane how good you are at explaining complex topics. I never feel "burned out" from watching your videos

[sholinwright]

I’d love to see the symmetry vs conservation topic presented this way. I wished there was a simplified scenario where conservation of energy could follow from a given symmetry.

[lattice]

More of these! This was an excellent gauge of my own level of understanding as an undergrad who is generally unsure of "where" I am!

[jorex]

I always liked the mathematical explanation of why the 1/2 factor occurs in this formula when you calculate the line integral ∫ F • dr

[vs]

Bro you speak so concisely and clearly about KE - a mark of a high level understanding. An important idea that I didn't think about is the idea from level 1 that energy is a number that allow description of what an object is doing or will do. I didn't ever really think about this, I just took the formulae and applied them using conservation of energy. Thank you for giving me this new understanding.

[MaximQuantum]

This video was amazing! It's basically a video introduction to roughly everything about kinetic energy, and even its formulas, yet explained so simply and teaching so many, so many new things! I'd love to see more of these!!!

[THBLCKHWK]

I definitely enjoyed the 5 levels video. Please keep using this structure. It really helps build an intuition for the concepts from low to high level.

[randymartin]

I'm in love with the way you explain things. It's so buttery and easy to digest. Thanks for the great vids!

[yatinannam]

I am still 15 yrs old and I understood QUANTUM MECHANICS by watching ur videos
Love from INDIA

[ZsoltCseresznye]

Hi Parth G,
About the different Reference Frames, at 5:43 you say:
"What really matter is how this energy changes" -- I like this approach, but I'd need a littlebit more explanation, for example:
If a 1000kgs car goes with 10 m/s then if it wants to accelerate by 10 m/s to reach the speed 20 m/s, it needs 150 kj energy to speed up, because this is the kinetic energy change it have to deal with.
If the same car wants to accelerate from 0 m/s to 10 m/s, it needs only 50 kj, because the change in kinetic energy from 0 to 10 m/s is less in this case, since the square of the speed in smaller absolute values matter less, than in bigger absolute values.
And here is the seemingly problematic contradiction with different frame of references.
In the first scenario, if we are sitting in another car and go paralelly with the same speed as the first car, 10 m/s, then from our point of view the first car needs to consume only 50 kj energy, since from our reference it accelerates from 0 to 10 m/s.
Can you please describe this seemingly contradicting energy change differences in an intuitive way?
Thank you

[MuhammadAli-lgkz]

Parth love you, you are making great videos. Keep up making.

[bernardputersznit]

love your 5 levels explanatory methodology here and elsewhere - it's a brilliant way to seamlessly develop a student's understanding - please do keep these coming Parth

[martifingers]

Just exactly what I needed. Excellent format and exceptionally clear.

[soulintent]

This video was really lot of fun, i hope you do more of these, i suggest you do a video about the notion of dimension in different levels of difficulty, would be interesting, it s done before but i wanna see you do it your own way

[Artham-xo]

Thankyou for solving all of my doubts !!! ❤❤

[skepticsapiens]

I would say just one thing - Never stop making these videos.