Energy Systems Clarified

[@fireemblem2770]

I am online for university and struggling with physics... but not really anymore. I saw your videos the first week of class and have been enjoying them ever since. This is my third time taking physics, and my first time taking physics online. I finally feel like I am learning something. Thank you so so much Mr. P!!!

[@FlippingPhysics]

Happy to help!

[@cupostuff9929]

dude, these videos are actually so good! I've finished AP physics 1 & I felt pretty confident with my ability in the class though watching these videos gives me even more insight since no fact is hand-waved away & all assumptions are laid out

[@FlippingPhysics]

Thanks for this lovely comment!

[@enoch1680]

This is a super helpful video. One clarification that I would suggest you include is that when you say including the board means that all energy stays in the system, you clarify that you are assuming that the heat generated from friction heats the board and not the surrounding atmosphere. When the air warms, energy leaves the system.

[@FlippingPhysics]

Valid point. Thanks!

[@tanzilatasnim7446]

I really like this channel! Underrated tbh

[@freddibiri]

very intuitive as usual

[@FlippingPhysics]

Glad you think so

[@hheli506]

HI, very nice video! I was wondering why the kinetic friction force is the directed downward. shouldn't it be upward? thank you:)

[@FlippingPhysics]

The block is sliding up the incline. The force of kinetic friction opposes motion, so it is opposite the direction the block is moving. Therefore, the force of kinetic friction is down the incline.

[@eaglekraft687]

So when you have a force (like the force of gravity) internal to the system, we don't look at it as the work done by the force of gravity but rather the gravitational potential energy. Is this because the work is just the transfer of energy so it makes sense to use the work done by the force of gravity because that's just saying how everything external to the system transfer's gravitational energy to the system. However when we include earth in the system, we have to start using gravitational potential energy because we are looking at how that energy changed and how it can be converted to other energies (like KE). Work done by the force of gravity would make no sense because since Earth is in the system, energy wouldn't be transferred. Is this right?

[@michaeln5448]

I started watching your channel at the beginning of the school year and after reviewing/taking notes on a considerable amount of them, I think I did well on the (physical) AP Physics 1 exam yesterday. Thanks a lot, and are you going to do the 2021 FRQs for Physics 1, which are probably going to be released tomorrow?

[@gwanpilson]

What did you get (if you don't mind sharing)?

[@abdulmohsen0]

This video is awesome, thank you!!

[@Lovemesomuch97328]

Also human energy can transform in to others or effect by some kind of human energy?Especially who is in Golden age

[@uhkneerudh]

very nice

[@aasimali6937]

Mr.P I request you to add a fourth desk in the classroom. Please!!!!!!!!!!!!!!!!!!!!!!

[@katharinabeck7709]

Plz can anyone explain how to choose your system?

[@science1878]

The system you choose should include the objects participating in the energy transfers you care about analyzing; anything that directly interacts or exchanges energy with your objects of interest should be included in the system.It's usually a good idea for the system to be isolated or self-contained as much as possible; surroundings that don't actively participate can be left outside the system boundary.

[@chipomwika6824]

Thanx 👌👍👍

[@mikeolson6837]

Nice

[@minh9a368]

hi, i still don't understand why system don't have PEg or PEe

[@getdroppedson7799]

You mention that it is not possible to measure the potential energy of an object if the object is the system. The reason being that potential energy is relative and thus requires an external reference point, which is not possible if only the object is defined as the system. However, you say that it is possible to measure the kinetic energy, but I don't see how. Kinetic energy is proportional to the velocity of the object, and velocity is relative. This means you would need an external reference point in order to measure the kinetic energy of an object and that is not possible if the object is the system. Am I wrong?

[@planeenthusiast9044]

yes.

[@science1878]

im pretty sure he said that we cant measure the gravitational potential energy because our system only includes one object (the block) and the earth is not in the system; gravitational potential energy only exists when there is a force of gravity, and since the force of gravity is the attracttion force between TWO masses or objects then there is no force of gravity in our system(so no gravitational potential energy). The same is for the elastic potential energy, the spring is not in the system so no spring force and no elastic potential energy. However the kinetic energy only depends on the motion of the object, so since we have an object in our system and it moves then kinetic energy exists. Hope this helps

[@gabi-dh9eo]

Hi!

[@krishkapoor2422]

first