@kairanadotoe22 Yeah, theoretically it does because if you dug a hole under someone they would fall. Because gravity is always acting on you, and because the earth is always applying a normal force on your body, you always contain potential energy. I suppose if you lived on a planet with a mass smaller than yours, then you wouldn't contain potential energy, but on earth you do.
for the sake of this world and next generations to come, you should join forces and work with PatrickJMT and Derek Owens to create the perfect and ultimate math and physic encyclopedia.
so, you said it takes the elevator a force of mg to counteract gravity and move up a certain distance. but doesn't it take more than mg. In other words, if it just doesnt move, doesnt that mean the elevator is in equilibrium? I would think that it would require more force than mg to move up.
@bmgag19 uhm yeah, if the upward force is the same with the downward force it musnt be moving... uhm, did you figure this out already? i mean, do u already know the answer to your own question?
THANK YOU VERY MUCH!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! im taking calculus based physics in college, and although these are just the the basic concepts, you have no idea how much this helped...i wish my prof was like you..all he does is show up and do problems without explaining the concept first...in my opinion, without a firm grasp of the basic concept, physics is torture..But once you get the concept, its quite interesting and enjoyable...second thanks....im buying your app
@Calilifestyle89 thats so true cuz i started physics last year and that teacher just did equations without explaining and now im in my second year with a new teacher who is trying but its not working...and its torture for the students and the teacher but its his job to teach so
Sal (or anybody that knows), I would REALLY appreciate it if you could explain W(other) = /\KE + /\PE. It's not in my physics book (Shaum's Outlines: Physics, 10th) and my physics professor said you can't algebraically derive it and this is driving me crazy. It really seems like it should be [Epsilon]W for the Free Body Diagram but he said this isn't true, and didn't care to elaborate.
It has to do with diferential and integral calculus. Force as a conservative vector field is equal to minus de gradient of the field. On the other side, is the Integral of F dx. Being a definite integral and with the gauss divergence theorem, they are equal and will be what you said!
great video, very helpful...but i must ask...if there was an exam/test or w/e should i represent gravity as 9.8 or as 10...you used... both...so i'm not quite sure...
I've learned that college professors want students to use 9.8 on tests and homework. My philosophy, when in doubt use exact numbers. Why fall into a rounding errors when you have the exact numbers! :) Hope this helps!
They ususally specify......or u can just ask the teacher..its not that complicated...if u dont know just ask since both is sometimes used like Sal did. In physics the BEST thing to do would be to use 9.81...while in Mechanics in math, the BEST one would be 10.....These are what is almost always used for each subject...but just ask to make sure.
heres a potential energy problem (gr. 11 physics):
a man decides to climb an office tower using the stairs. if the floors are 3.8m apart, how much gravitation potential energy would the man have relative to the ground floor if he made it to the fifth floor?
(i cant get this because it doesnt state his mass, is there still a way of solving?...something to ponder)
Force is a vector. So the direction it is being applied matters.
If the force is being applied at an angle to the direction of the movement, the cosine of that angle will tell you how much force is being applied in the direction of movement. So work would be force times distance times cosine of that angle.
In Sal's example, the force is being applied with an angle of zero, so cosine of zero is one, and one times force time distance is the equation Sal gives.
THE best action ending, it's like a T.V. show.
Will the object ever hit the ground stay tuned?
for the next video!
makbadwan 2 days ago
some sweet info here
rodswebdesign 1 month ago
i cant thank u enough khan.also i love that way you always say I DONT KNOW and u know...lol
stfrankies240 1 month ago
I am very happy to see the vidoe More on work. Introduction to Kinetic and Potential Energies. after you give this
Kricardose 1 month ago
I Love The Video More on work. Introduction to Kinetic and Potential Energies It Can Increase My Knowledge
bebeheuy 1 month ago
Steady I Really Like This Video Introduction to Kinetic and Potential Energies.
Mjhond 1 month ago
the best answer.
MrPEDOCTOR 2 months ago
headache
adamaqmal 3 months ago
i think you meant 122.5 not 125 because 1/2x5x49=122.5 i didn't get 125...
DeloresTBH 3 months ago
@DeloresTBH you do know what approximately means, right?
SickOfSillyPeople 2 months ago in playlist Physics 2
improve your handwriting
dude
nihaldivyam 3 months ago
@nihaldivyam as long as you understand what he's teaching you, his handwriting shouldn't be a problem.
cspower12 3 months ago
@nihaldivyam its on a computer retard
TheBurgooKing 3 months ago
@nihaldivyam let's see how well you could write on paint
tool
miraslam2000 3 months ago
only good thing is: i didnt pay you money for this lousy explanation.
tekal85 4 months ago
awesome knowledge source
piyush4left 5 months ago
1/2 x 5=2.5 x 49 = 122.5, not 125.
facedown220 7 months ago
And one more thing.... are you saying that a body contains potential energy when its in a state of rest?
kairanadotoe22 7 months ago
@kairanadotoe22 Yeah, theoretically it does because if you dug a hole under someone they would fall. Because gravity is always acting on you, and because the earth is always applying a normal force on your body, you always contain potential energy. I suppose if you lived on a planet with a mass smaller than yours, then you wouldn't contain potential energy, but on earth you do.
MattMahael 3 months ago
but isnt g taken as negative or something since the body moves against gravity..so therefore the ans becomes negative?
kairanadotoe22 7 months ago
I loveit how every video from khan academy has 6 dislikes
Chantheman5 7 months ago
g is not equal to -9.81?, since elevator is moving upward!
gpak47 8 months ago
@gpak47 but the pull of gravity is the still going to be the same (9.8N/kg)
francais2121 7 months ago
@gpak47 Gravity is pulling downwards on the object which means more work to make the elevator go upward.
elitegence 6 months ago
for the sake of this world and next generations to come, you should join forces and work with PatrickJMT and Derek Owens to create the perfect and ultimate math and physic encyclopedia.
fafase 10 months ago 4
Next Video: /watch?v=kw_4Loo1HR4&feature=fvwrel
its named Conservation of energy not part 3
fuzzyhunty 10 months ago
How much work is being done on the elevator?
OVER 9000!!!!
its123baby 11 months ago
Where is part 3?
wearebeetlejuice 11 months ago
i said that 2 times LOL :D cooooooool vid
mohtaprashant 1 year ago
4:30 sniff! hehe. i also have a cold when i first watched this.
got it. now i'm ready for tomorrow's report.
vincetheworldly537 1 year ago
whats the next video , i tried searching work and energy (part 3)
bossman6821 1 year ago
first thank you it's easy but our professor always make things complicated
second thing stop moving the mouse alot it make me nervous
ahlawy1993 1 year ago
so, you said it takes the elevator a force of mg to counteract gravity and move up a certain distance. but doesn't it take more than mg. In other words, if it just doesnt move, doesnt that mean the elevator is in equilibrium? I would think that it would require more force than mg to move up.
bmgag19 1 year ago
@bmgag19 uhm yeah, if the upward force is the same with the downward force it musnt be moving... uhm, did you figure this out already? i mean, do u already know the answer to your own question?
vincetheworldly537 1 year ago
THANK YOU VERY MUCH!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! im taking calculus based physics in college, and although these are just the the basic concepts, you have no idea how much this helped...i wish my prof was like you..all he does is show up and do problems without explaining the concept first...in my opinion, without a firm grasp of the basic concept, physics is torture..But once you get the concept, its quite interesting and enjoyable...second thanks....im buying your app
Calilifestyle89 1 year ago 2
@Calilifestyle89 thats so true cuz i started physics last year and that teacher just did equations without explaining and now im in my second year with a new teacher who is trying but its not working...and its torture for the students and the teacher but its his job to teach so
rabalac99 1 year ago
Like clock weights on a cuckoo clock
djwildmanmike 1 year ago
i still can't get over how good this guys videos are,
how does he get money?
edwebo 1 year ago
9.81
kmiller1985 2 years ago
9.81 ftw!
rbndelrio 2 years ago 25
Sal (or anybody that knows), I would REALLY appreciate it if you could explain W(other) = /\KE + /\PE. It's not in my physics book (Shaum's Outlines: Physics, 10th) and my physics professor said you can't algebraically derive it and this is driving me crazy. It really seems like it should be [Epsilon]W for the Free Body Diagram but he said this isn't true, and didn't care to elaborate.
AverageJoe8686 2 years ago
ΔPE+ΔKE=0
so ΔPE=-ΔKE
If PE decreases, then KE increases and vice versa.
wcsummer 2 years ago
It has to do with diferential and integral calculus. Force as a conservative vector field is equal to minus de gradient of the field. On the other side, is the Integral of F dx. Being a definite integral and with the gauss divergence theorem, they are equal and will be what you said!
beautiful :D
RogerTiger 2 years ago
great video, very helpful...but i must ask...if there was an exam/test or w/e should i represent gravity as 9.8 or as 10...you used... both...so i'm not quite sure...
someone please answer
thank you =)
mozillafirefox92 2 years ago
I've learned that college professors want students to use 9.8 on tests and homework. My philosophy, when in doubt use exact numbers. Why fall into a rounding errors when you have the exact numbers! :) Hope this helps!
Digits571 2 years ago
9.8. he used 10 cuz he wanted to simplify the calculation, since he didnt want to use the calculator all the time.
xlwaiyiplx 2 years ago 2
9.8
benjoandrichie 2 years ago
They ususally specify......or u can just ask the teacher..its not that complicated...if u dont know just ask since both is sometimes used like Sal did. In physics the BEST thing to do would be to use 9.81...while in Mechanics in math, the BEST one would be 10.....These are what is almost always used for each subject...but just ask to make sure.
otuonyec 2 years ago
9.8m/s^2
10m/s^s is for people who are lazy and don't care if the numbers are a little off.
MUsnaredrummer 2 years ago
it depends on which test and which teacher you have. if you get to use you calculator use 9.8 but if you are taking the MCATs use 10
HPPcello2 2 years ago 15
Thanks dude, great videos!!!
caseypena420 2 years ago 2
Your videos regarding E&M are very helpful. Thanks.
puglyfeet 3 years ago
I concur!
woodenjaw 2 years ago
wat if you had 2 velocity...i have a problem where i need to find the height of a hill and i have 2 velocities...wat should i use for my formula?
Havardgurl 3 years ago
heres a potential energy problem (gr. 11 physics):
a man decides to climb an office tower using the stairs. if the floors are 3.8m apart, how much gravitation potential energy would the man have relative to the ground floor if he made it to the fifth floor?
(i cant get this because it doesnt state his mass, is there still a way of solving?...something to ponder)
honeypot11 3 years ago
OMG i didtn get that one either! how r u supposed to get the answer if you dont know the mass?!
monaegr 3 years ago
isnt work = force * distance * cos Θ ?
RafidHoda 3 years ago
Force is a vector. So the direction it is being applied matters.
If the force is being applied at an angle to the direction of the movement, the cosine of that angle will tell you how much force is being applied in the direction of movement. So work would be force times distance times cosine of that angle.
In Sal's example, the force is being applied with an angle of zero, so cosine of zero is one, and one times force time distance is the equation Sal gives.
Hope that helps...
Shazaaming 3 years ago
no that would be if your dealing with angles. In a general sence work = force * distance
Katianie9 2 years ago
THANK YOU!!! the eqn for gravitational potential energy makes sense now!!
brvheavyhitter20 3 years ago
yo Professor
BigDragonBanglo 3 years ago
I like your teachings a lot ! You should become a professor !
idricool 3 years ago 2