Work and Energy
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- Опубліковано 25 січ 2025
- What's work? Not that place you go to earn money. In physics it means something else. And what's energy? Not like in the groovy sense. Actually, energy is one of the most improperly used words in the English language. Let physics define these words for you!
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intro: professor so kiddish
video: very serious
We are trying to learn and you here doing memes😂
truth
riggght ....but also he looks so jewish too
Maot kaayo
@@ezzo3788 😂😂😂😂
Thank you soooooo much for making these videos. I know you have helped tons of students understanding the subjects more.
ua-cam.com/video/Vw8U2dW03eY/v-deo.html
😀😃😃😄😍😆🙂😊😇🥰😍🤩😘😗
This man just summed up 3 hours of me reading the textbook in about 5 minutes... Truly good stuff and easy to understand. Thank you Hendy
Hello, This guy actually teaches you more in 5 minutes than your teacher in an entire semester.
"Colloquial connotations." Love it. It's a polite way of saying, "Don't embarrass yourself."
thanks dad
Ur welcome
@@DudeWhoSaysDeez no your patrick
What is he u r dad 😀😀That seems to be weird
@@devendrareddy816 hes ur dad as well.
He is Jesus
You know you never really use too many examples or if you do they are simple, but honestly that should be the way they initial teach. It really helps me understand where things come from before practicing the actual examples later.
Thanks!
The introduction of cosine and its values influencing the amount of work really blew my mind for some reason. Being able to quantify things like that really makes me appreciate this crazy universe. These videos are immensely valuable and you are one of the reasons I have chosen to pursue an education in physics
I didn't know Dave Grohl knew so much about Physics!
legit the most helpful channel ive ever encountered for my physics class
Thank you smmmm!!! You're honestly physics Jesus who's going to help me more than my physics teacher ever will for HSC
my teachers' so lazy that she just tells us to search the lessons at home : /////
WutFace
That’s a terrible teacher our teacher gives us a book and notebooks and tells us its do tomorrow
Uhhhh same 😑😞
she was prepping you for the apocalypse
Lmao basically online class
This is so helpful it covered all that I needed for my quarter exam
Dear Dave: my appreciation for this excellent , simple and interesting explanation
I felt bamboozled knowing that this is the first video that I’ve seen that did not include comprehension in the end. But nonetheless you’re explanation are always superb thank you very much!
bruh do we rly need this shit for life
thanks very much for the explanations i am having a test tomorrow about work and energy and i feel much clever after i watched this video and i like the way you explain work and energy i cant wait to see more of your videos about KE and PE thanks for the video now even my sister carly can understand
5 years too late - but I hope the test went well for you.
Okay. So here is a very fundamental doubt.
We know that work = energy. (It definitely is. Because,
work=fd= 1/2mv(v)= energy
And energy is the ability to do work..(1)
That implies
Work=ability to do work (using (1))?😮😮
How can two things which are exactly equal can be different from each other?
im so happy i found a youtuber that can help me with bioligy,chemistry and physicis this means so much to me.. u have no idea how ur helping me with my finals :)
My man getting me right! We all appreciate your hard work.
I am learning a lot from you Professor Dave! Thank you so much po!
Watching this but I know I’m still going to fail my AP Physics exam lol
did you pass, how should i survive if i fail
SHAAN KUMAR what did u get??
Don't worry , believe in physics jesus
@@kawaichanx3 thats a holy name bruh
I've never understood these problems without you, thank you very very much bro. You're my professor. ❤ love frome 🇹🇭 🇹🇭 🇹🇭 🇹🇭.
after watching his video for 3 times with the video from CrashCourse 2 times now i understand it with a smile face. We love you Pro Dave
In physics, "work" is when a force applied to an object moves the object in the same direction as the force. If someone pushes against a wall, no work is done on the wall because it does not move. However, depressing a letter on a computer keyboard requires work.
2:55 When you give your sibling an unplugged controller
Hi, i am a student in grade six. Can you please explain what theta, cos and work-energy theorm? Thank you 🙏🏻
check out my mathematics playlist! or more specifically my trigonometry playlist.
Theeta is a greek letter, just like we use 'x' and 'y' to mark angles. Cos theeta means the effect of that force in the horizontal direction. For example if you hit a football in north-east direction, actually it had travelled in two perpendicular directions, north and east...the force which contributed for the force only to travel to east means Fcos(theeta)..its something like that..... And work energy theorem means that, the more energy u have, the more u can transfer it and do work...just like if u have more money, you can spend to buy more things and vice versa.. in physics, that spending to buy part should be replaced by 'making an object move'(do work)
This is so perfect. I needed something that teaches me how to do problems but in a very easy and fun way.
Thank you so much Sir!!! I learn a lot from you!!! You're a blessing to students just like me who can't easily catch up with what their professors where teaching! Again, Thank you so much!! ❤
Love the intro.. 💫💫
I thought scaler numbers couldn’t be negative?
I'm a bit confused on when to use W=Fd vs. W=Fdcostheta
first one if force is applied in direction of motion and second one if at an angle
You will notice that when theta equals zero, cosine of theta reduces to 1. Thus you will get the same answer as if you had calculated W=F*d*cos(theta), or W=F*d itself.
The full generalized form of the work definition equation is:
W = integral F dot dx
where F is a vector at every point along the way, and dx the various infinitesimal displacement vectors that add up to the full path length. This reduces to a single dot product of force dot displacement (W = F dot d) when the force is constant at every point along the way, and the displacement is a simple straight line. The dot product is a special kind of multiplication that multiplies the aligned components of two vectors, hence the cosine term that develops.
Since d already has another full time job in Calculus, it is common to use another letter to indicate displacement, such as x or s.
Am starting to love his ways😭❤️ specifically the introduction 🙌🤣🤣
This makes me think of the old expression every young man is scolded/initiated with into the world of manual labor:
*”Let the tool do the work!”* - so.. the reason why we quickly came to realize just how wise this initially irritating/inane advice really was, is because according to the laws of physics work-energy theorem: We only do the work of changing the kinetic energy of the tool, but only the tool’s energy of motion can now do “the work”.. so ya, let the tool do the work!
Professor Dave is awesome, thank you so much
Matt Z Ditto. Great way to understand what energy is.
it is really big help to me. thank you
Baby brother is pushing you with 1newton force and final work is 6N.m
Thank you Professor Dave 👍👍👍
can anyone help me ?@2:11 why work is multiplied by cosine & not sine ??i mean he mentioned because it going to give us the portion of the applied force horizontally but i meant logically why?
because cosine is adjacent over hypotenuse, and the component of the applied force that is contributing to horizontal motion is the leg that is adjacent to the angle!
Wow,you replied yourself,thanx alot
But why calculating only the horizontal work not only the vertical, maybe the vertical force is greater than the horizontal one
@@ibrahimmuhammad270 horizontal work only contributes towards displacement here not the vertical
Sir your teaching method is very easy and outstanding 🙏🙏🙏👍👍👍👍
Hi,
May I ask which mode should be used when there is an angle given? I have seen some used degrees and some used radians. I did try using online calculators and got different results.
Thanks!
You need to look at the units on the angle given. There will usually be a degree sign if it is in degrees, and if it is in radians, it will usually contain pi and no unit specified (since rational number of degrees end up with pi in the numerator for radians). Configure the mode of your calculator to be consistent.
If your calculator doesn't have the ability to configure the mode, most likely the default mode is radians. Read the help text of the program or calculator to understand its conventions. For Google Calculator, type " degrees" after typing the number, as the input to the cosine function. This will override its default units of radians. For Microsoft Excel, type cos(radians(30)) to calculate the cosine of 30 degrees. The radians() function converts from degrees to radians, and Excel requires radians with no direct way to override its default.
I do recommend reading about what radians are, because they are a great angle unit that makes the Calculus of trig functions as simple and elegant as it an be. And I don't just mean learning that 180 degrees = pi radians, although that is an important thing to know about the unit as well. I mean learning a geometric interpretation of what 1 radian really is, and what motivates us to define the angle unit. Its name comes from "radius angle".
Thanks for this video, Professor. A blessed day, everyone!
Thank you Mr. Dave, this is such a great summary; simply packed (?) and brief. I would like to share this on physics class.
Please do continue doing this sort of video, you really did help me with many of my assignments at school, I often come back watching your videos if I need help on what kind of phrasing should I use to be more understandable.
Also, the jokes. It's great.
But, F=ma, W=Fd, W=dma, W=dmd/t², W=m×d²/t², W=m×v²
KE=0.5mv²
W=mv²
W=2×KE
?W=∆KE
∆KE=KE1-KE2
What is going on, please help.
Why is it only half of an objects mass in the formula for Kenetic Energy?
1:34 When somebody spends their entire life trying to prove that the earth is flat:
This really helped me prepare for my test.
Once again dude thank you
omg, i wish my teacher could explain physics like you! i'm gonna drop outttt.....loollllz
i love you P. Dave
The second law of thermodynamics (part of it) is that all physical processes create entropy and entropy the amount of energy not available to do work. It, along with the first law is the reason you can't create a perpetual motion machine, all the energy will "turn useless" which is the second part, that all the energy will become entropic in a closed system. Still trying to figure out entropy so that's why I bring this up.
yep it's a multifaceted law! can be expressed in a variety of ways.
So, if take the perpetual motion machine example, say a machine that (well, it doesn't succeed obviously) that is a closed system and tries to recycle the energy into itself, stops working, how? It's able to do it, initially, but then eventually it can't, what is going on? I'm trying to think of an example of something we could try to make into a perpetual motion machine that would obviously fail to do so, so I can try to figure it out. I'd say water that falls turning a wheel, in which the wheel pumps the water back up to fall on itself to turn it, but that's not exactly closed, because what starts the wheel turning in the first place?
A perpetual motion machine could exist in theory, if you were able to eliminate all losses, such as friction, viscosity, drag, and ohmic resistance. But the minute you try to extract any energy out of it for any application at all, it will no longer be in perpetual motion. You will slow down the motion, and deplete its energy.
What people really mean by "a perpetual motion machine", is really a more like a perpetual WORK machine. A machine that can continuously deliver a work output, without any work input. It doesn't exist in reality.
A planet in orbit around a star is one example of what would technically be a perpetual motion machine by the direct meaning of the words. But if you were to extract work out of the orbital speed of the planet to power your own machine, the planet will not keep orbiting at the same position. Its orbital energy will decrease, and its orbital radius (or more generally, semimajor axis) will also decrease. Continue extracting energy, and it will end up on a crash trajectory with the star.
Wow! your's voice is superb
Of which branch of Physics these concepts are????
Mechanics
I have a question professor Dave if you push the box at 90° and the box moves downward then the applied force is now parallel to the displacement of the object, I think there is work done given the definition of work
In this example, the box doesn't move downward, because it is constrained by the normal force from the floor. Assume we are talking about a rigid box and a rigid floor, rather than a compressible cardboard box.
Actually theta is the angle between force and displacement.In your situation the angle between force and displacement is still cos 0 as they are parallel to each other.remember that theta is not only the angle of force it is the angle between force and displacement
So if the work is negative that means the speed will decrease and vice versa right ? Does it works every time ?
Not necessarily. That is true if the NET work done on the object is negative, but not just the work in general.
Consider the example with you and your baby brother, both pushing a box. You push forward on it, and your baby brother being a little brat, pushes backwards on the box. Your baby brother is doing negative work on the box, but you are doing positive work on the box. It is possible that the both of you increase the speed of the box as a net result, because you do a lot more work than your baby brother. The net work is positive, even if your baby brother's contribution is negative and counterproductive to your effort.
1: 45 andddd 2:33
This lesson confused me. Work is equal to (magnitude of force) * (D)
is it distance or displacement (ik their differences but you interchange them at 1:08 )
and you said work is scalar
if the "D" in W=(F)(D) is displacement (thats what you and my professor said) then why is work a scalar quantity and not a vector quantity
Especially when you apply work on an object by an angle in which you must use a cos(x)
Work is the product between magnitude of force and magnitude of displacement. More technically, it's the dot product between force and displacement. So obviously work is a scalar quantity! Hope it helps
It is displacement. That is why the cosine(theta) develops in the equation. You are taking a dot product of force and displacement, as opposed to just a scalar multiplication of distance and force.
When the vectors are aligned, you get away with ignoring the fact that it is really displacement, and just multiplying magnitudes. But when vectors are not aligned, that's when you need to consider the cosine term to account for direction. Or you can use the "multiply corresponding components and add up the products" strategy of taking a dot product.
What would be the amount of work done if i apply a force of 10N on an of objet of 1kg in deep space and it travels for ever? Thanks
*Work = Force x Distance*
Work = ∞J (Joules)
@@user-fo4ue9mo4z Some thing does not add up here. how is this possible to do an infinite amount of work with just a 10N force?
Nash Nazer the force was 10N and the distance is ∞, because you said it travels forever
Therefore
Work = force x distance
Work = 10N x ∞
So work = ∞
@@user-fo4ue9mo4z In space it will travel for ever any way until disturbed
Very good Professor Dave
Excellent explanation.
what if we lift the box, would it make the work 0? because Fdcos90 is 0, that means w =0?
Thanks for your video, you explain it very well and in a short amount of time
Belated Happy Teachers Daaaaaaaaaaaayy~!
AP exam this Friday thank you professor Dave 👍👍👍👍
Clearly explained. Thank you
Thank you so much 🎉
thank u dave 🤘 my advisor makes me watch these videos and as much as i hate working i learn a lot in these videos
I love your tutorial sir
How about when you consider no friction or other external forces like a rocket in empty space. If you have thrusters that apply a certain force N, it accelerates from stationary to high speeds according to a = F/m. But since work is proportional to the distance, do the first 1000km take the same amount of work as say a 1000 km when it is already flying at high speed? at those speeds the same distance is traveled in a much shorter time so the engine is pushing at the same force for a shorter amount of time, so it looks like its using less work for the same distance. I know I am missing something here so can someone explain? does it only make sense if you are not talking about acceleration?
Thank you so much ! Really appreciate it ❤
Thank you very much professor Dave, I had a lot of doubts but after watching this. It all makes sense now, thanks again!
You are my best teachers sir
When we apply force to an object it'll cover infite distance (1st law of motion) but it actually nor happens due to friction so technically friction opposed the force we applied so how does it related to energy ? You doing the same work on rough surface and plan surface so how does you get kore tired there since you apllied the same energy
Do you have videos for conservation of momentum, radial acceleration, potential and kinetic energy equation examples? Please it would help a lot with physics
check out my classical physics playlist it's all in there!
i love the shirt that you wearing every physics leacture. LOL
Thanks very much pro
I attend your videos always and I got more knowledge from your teaching.
you are such a great teacher, thanks for your effort
Any comments pls ua-cam.com/video/Vw8U2dW03eY/v-deo.html
Sir as u said, work may be positive or negative..
But work is a scalar quantity
we just use positive and negative values to distinguish between work done on a system and work done by a system.
Thank you so much sir you are helping us a lot thank you so much ❤
why shouldnt we consider the y-components when caculating work??
we do! We use the formula W=mgh, m being mass, g being acceleration due to gravity and h being height but this is only when we're lifting things that is, no horizontal displacement
You just got a new sub
He is amazing.... Want more
Mr.Dave,in a previous video, you explained that scalers don't have negative magnitude, could you clarify how work has a positive and negative magnitude although it is considered as a scaler, plz?
Some scalars can be negative. Some make no sense for them to be negative.
Some examples of scalars that can be negative:
Work
Potential energy
Voltage
Current
Power
Divergence
Money (e.g. debt)
Electrical charge
Outputs of trigonometry functions
Some examples of scalars that make no sense to have negative values:
Speed
Distance
Length
Volume
Mass
Kinetic Energy
Coefficient of restitution
Coefficient of friction
Temperature in the absolute scales of Kelvin and Rankine
What if you lift the box above? There will be a distance right? But mathematically it will be zero because cos(90) = 0
Why is that?
If you lift the box, but not strong enough to lift it anywhere, the work will be zero. You apply a force, but that force is unsuccessful in doing anything.
If you lift the box and it moves upward, there will be a distance that is directly upward. The angle isn't 90 degrees, but rather it is zero, and the cosine is 1. This isn't the angle from the horizontal, but rather the angle between the force and the direction it moves.
Thankful professor ❤💜
Omg you are literally god thank you so much😭❤️
Nice sir
Did u say work is scalar?😮
love your intro 🙂
Can you please derived the formula of Work
The real father of physics.
Good Explaination. @
If we push an object in space and that object keeps accelerating assume it gets infinite velocity at infinite displacement..we get work as F*infinity....which will be very large offcourse (infinite ) here kinetic energy Is also increasing and work is also being done....how is it possible that work is done and energy is gained !
Pls stop discovering. I've had enough of physics history
If you don't understand,it's probably coz your looking at professor Dave the whole time...
Happened to me!
hi great video, I thought scalars cannot be negative? (time stamp 2.37) did you mean vector?
Scalars can be negative. Some scalars make no sense as negative numbers, others are used as negative numbers all the time.
Some scalars make no sense as negative numbers, like speed, mass and volume. There are also scalars that make sense when using in relative scales, like temperature, pressure, and elevation, but ultimately are positive in absolute scales. Additionally, some scalars are defined in with an arbitrary zero point is, and thus can be either positive or negative. Potential energy, and related concepts like voltage, are examples.
Beyond that, there are scalars that have a nature to make sense in both signs, such as electrical charge. Work is one such example that makes sense as a negative number, because it simply means that the agent of the force receives the energy, instead of providing the energy.
@@carultch thank you for the detailed response :)
There are def some people that don't use "energy" metaphorically, lol
Isn't work a vector quantity if it can be both negative and positive
The ability for a quantity to be both negative and positive, doesn't imply that it is a vector quantity. For instance, electrical charge is also a quantity that can be both positive and negative, but it is certainly a scalar quantity.
Work is a scalar quantity as well, even though it can be both positive and negative. The interpretation of the sign of work, tells you whether it is done on the object (positive), or done by the object (negative).
Thank you ser for helping me out
I like the intro very much
thank you. God bless
U r amazing Dave😊
Where can I get all your videos in any topic please