Is the pulley being pulled to the left because of the friction or is it because something else. I don't understand this part 100 % I hope someone point me to right intuition.
In 7:23 Why is the pulley is being pulled to the left I don't understand this can someone explain this to me,since he is already pulling to the right it wouldn't make sense. Can someone please explain this to me.
@chrispikeyp In 7:23 Why is the pulley is being pulled to the left I don't understand this can someone explain this to me,since he is already pulling to the right it wouldn't make sense. Can someone please explain this to me.
I never took physics and I know you're off by some amount. You did not account for the friction of the rope against the surface of the pully, the weight of the rope itself, and the friction of the pully against its axle. I'm kind of glad I didn't take physics because I would have probably been kicked out for nit picking the teacher :)
If the pulley has mass you have to account for the effects of rotation, plus the tension in the string at the top is NOT equal to the tension of the string at the bottom!
You have to add the distance the bottom string moved (1inch) plus the distance the bottom mass moved (1 inch) as a result of the bottom string getting shorter by that distance (equivalent) to get the distance the WHOLE system moved as a unit in itself, of course discounting the other of the system, which is the top unit. Diving this new value by 2, or just getting half, will give how much was added to the other half of the system (the top in this case). This is how I conceptualize the problem.
in a, the distance from the wall to the pulley is the same as the top length of rope which is m.
the distance to the brick from the wall is (m - n)
in b, the pulley goes forward by a units, so the top length of wire is now (m + a), and the bottom is (n - a) since that length is taken from the bottom as the rope is fixed length.
the distance of the brick from the WALL, not the pulley is (m + a) - (n - a) or (m - n) + 2a... so in time t it moved 2a
At first it seems like twisted logic, but I'm gonna make this simple.
When the pulley goes one inch forward, it just physically goes one inch forward. Nothing surprising there.
When the bottom rope goes one inch forward, it: 1. physically moves over by one inch. 2. The length of the bottom rope shortens by one inch to compensate for the forward movement. 1 inch + 1 inch = two inches. Yay.
Someone correct me if I'm wrong, so the block moves twice as far as the pulley because 1) the pulley moves 1in and therefore drags the block 1in and 2) because the pulley moves 1in, the wire is 1in shorter on the bottom, so that also pulls the block another 1in. so 1in + 1in = 2in?
"If the pulley moves 1 inch to the right, then this length (top side) will get 1 inch longer; and this length of rope (bottom side), because the rope is of a constant length, will get 1 inch shorter, so not only did the pulley move 1 inch to the right, but this rope right here got 1 inch shorter, so this block (attached to bottom) would've moved 2 inches to the right!"
There's a leap in logic, if I'm any judge. Both sides would get equally longer/shorter if neither side were stationary, though.
Actually, I see now. When one side of the rope is stationary, the tail of the moving side travels double the distance of the end of the stationary side against the pulley, but the rope's length itself remains directly proportionate on both sides.
Distance traveled and length of rope are two completely different things (distance includes displacement by the pulley AND change in length of rope on that particular side).
In relation to the length of the top wire and the bottom wire, that is correct.
The block moves 1 inch closer to the pulley, and the wire on the bottom moves 1 inch to the right because the wire cannot expand. Thus, the block must move an additional 1 inch to the right (equalling 2").
I think he inserted energy into the equation. For instance: Lets say he jerked the mass block with a big truck going real fast. The cable will be the same length, one inch, but the block will move two inches, so now, we have slack in the cable, or "wire" as he refers to it. In his example, we have one inch of slack in the cable on the bottom side and a block that has been move two inches. Think about it.
OMG thank you so much. My prof was explaining this today but she based it on the length of the wire only and not the mass (something like L/2) and then she went to the assumption a = 2a and nobody understood (and she wouldn't even explain her steps again with everyone asking her). Now I get it:D
the 10kg doesn't get closer to the pulley by 2 inches...it just moves 2 inches from your perspective. So the mass actually gets closer to the pulley by 1inch.
Is the pulley being pulled to the left because of the friction or is it because something else. I don't understand this part 100 % I hope someone point me to right intuition.
GenericCoder 1 month ago
In 7:23 Why is the pulley is being pulled to the left I don't understand this can someone explain this to me,since he is already pulling to the right it wouldn't make sense. Can someone please explain this to me.
GenericCoder 1 month ago
Very enjoyable thank you
chrispikeyp 1 month ago
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@chrispikeyp In 7:23 Why is the pulley is being pulled to the left I don't understand this can someone explain this to me,since he is already pulling to the right it wouldn't make sense. Can someone please explain this to me.
GenericCoder 1 month ago
interesting video and very informative
smuggecko 1 month ago
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I am very happy to see the vidoe What happens when we pull on a pulley and the pulley is pulling on other things after you give this
Kricardose 2 months ago
I Love The Video What happens when we pull on a pulley and the pulley is pulling on other things It Can Increase My Knowledge
bebeheuy 2 months ago
Steady I Really Like This Video What happens when we pull on a pulley and the pulley is pulling on other things
Mjhond 2 months ago
Man....I need this dude in my brain when taking my tests....SMART! ...and easy to follow! THANNNKSSS :)
PeaceHopeLove2012 2 months ago in playlist More videos from khanacademy 2
I need to do more exercise
MrPEDOCTOR 2 months ago
i wish he helped me in spanish cuz my teacher suxxxxxxxx
n i dont wanna fail
vernaghimire 2 months ago
at 3:06 it makes perfect sense!
AnotherBrownKid 3 months ago
XD pull on the pulley !
lawerdoggygirl 4 months ago
You make physics look like basic algebra, nice job!
desertfox1792 4 months ago
I never took physics and I know you're off by some amount. You did not account for the friction of the rope against the surface of the pully, the weight of the rope itself, and the friction of the pully against its axle. I'm kind of glad I didn't take physics because I would have probably been kicked out for nit picking the teacher :)
neamerjell 7 months ago
@neamerjell your arrogance blinds you of the fact that these problems assume an ideal system
plllll0 7 months ago in playlist Physics
@neamerjell are you a troll or actually that dumb?
konan439 6 months ago
@SerbAthiest
tension through out the rope remains equal, if the rope/string is inextensible.
thats a universal fact..
goldy2324957 10 months ago
What if the masses had 3:1 ratio? Even then the acceleration of the block would be twice than that of the pulley?
007fries 10 months ago
Fail!
If the pulley has mass you have to account for the effects of rotation, plus the tension in the string at the top is NOT equal to the tension of the string at the bottom!
SerbAtheist 1 year ago
You have to add the distance the bottom string moved (1inch) plus the distance the bottom mass moved (1 inch) as a result of the bottom string getting shorter by that distance (equivalent) to get the distance the WHOLE system moved as a unit in itself, of course discounting the other of the system, which is the top unit. Diving this new value by 2, or just getting half, will give how much was added to the other half of the system (the top in this case). This is how I conceptualize the problem.
EKon235 1 year ago
found it kinda hard to visualise the pulley and strings and why the bottom string was half the first- in its movement
naruto2710 1 year ago
please take my ph-211 final next week!
yusufforever 1 year ago
@timmytankTK I meant youtube is ruining the links I posted to a diagram. no need to be so bitter.
lumaix 1 year ago
i still havent realized the problem
MisticalWater 1 year ago
youtube is rubbish... to see my diagram, type in the address bar:
bit dot ly forward-slash aIbDPr
lumaix 1 year ago
Comment removed
lumaix 1 year ago
img121.imageshack.us/i/diagg.png
in a, the distance from the wall to the pulley is the same as the top length of rope which is m.
the distance to the brick from the wall is (m - n)
in b, the pulley goes forward by a units, so the top length of wire is now (m + a), and the bottom is (n - a) since that length is taken from the bottom as the rope is fixed length.
the distance of the brick from the WALL, not the pulley is (m + a) - (n - a) or (m - n) + 2a... so in time t it moved 2a
lumaix 1 year ago
Comment removed
lumaix 1 year ago
At first it seems like twisted logic, but I'm gonna make this simple.
When the pulley goes one inch forward, it just physically goes one inch forward. Nothing surprising there.
When the bottom rope goes one inch forward, it: 1. physically moves over by one inch. 2. The length of the bottom rope shortens by one inch to compensate for the forward movement. 1 inch + 1 inch = two inches. Yay.
leadershipcouncil 1 year ago
His voice is mesmerizing.
Chozo003 1 year ago 3
Very helpfull for the process behind solving a physics equation.
thumbus2003 1 year ago
Someone correct me if I'm wrong, so the block moves twice as far as the pulley because 1) the pulley moves 1in and therefore drags the block 1in and 2) because the pulley moves 1in, the wire is 1in shorter on the bottom, so that also pulls the block another 1in. so 1in + 1in = 2in?
fas890 1 year ago
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why dont u just say that differentiating velocity gives u acceleration.....i know its the same concept but its much quicker to say...:)
DarkLinxP 2 years ago
"If the pulley moves 1 inch to the right, then this length (top side) will get 1 inch longer; and this length of rope (bottom side), because the rope is of a constant length, will get 1 inch shorter, so not only did the pulley move 1 inch to the right, but this rope right here got 1 inch shorter, so this block (attached to bottom) would've moved 2 inches to the right!"
There's a leap in logic, if I'm any judge. Both sides would get equally longer/shorter if neither side were stationary, though.
vfmlor 2 years ago
Actually, I see now. When one side of the rope is stationary, the tail of the moving side travels double the distance of the end of the stationary side against the pulley, but the rope's length itself remains directly proportionate on both sides.
Distance traveled and length of rope are two completely different things (distance includes displacement by the pulley AND change in length of rope on that particular side).
vfmlor 2 years ago
In relation to the length of the top wire and the bottom wire, that is correct.
The block moves 1 inch closer to the pulley, and the wire on the bottom moves 1 inch to the right because the wire cannot expand. Thus, the block must move an additional 1 inch to the right (equalling 2").
inu1991yasha 2 years ago
I think he inserted energy into the equation. For instance: Lets say he jerked the mass block with a big truck going real fast. The cable will be the same length, one inch, but the block will move two inches, so now, we have slack in the cable, or "wire" as he refers to it. In his example, we have one inch of slack in the cable on the bottom side and a block that has been move two inches. Think about it.
Good luck :)
YouSpamTard 2 years ago
OMG thank you so much. My prof was explaining this today but she based it on the length of the wire only and not the mass (something like L/2) and then she went to the assumption a = 2a and nobody understood (and she wouldn't even explain her steps again with everyone asking her). Now I get it:D
will3330 2 years ago 2
ya my teacher is also same like yours..
6bikal6 2 years ago
i dont get it. if the bottom rope connected to the 10kg mass gets an inch shorter, why does the 10kg mass move 2 inch closer to the pulley?
ooziiee 2 years ago 2
the 10kg doesn't get closer to the pulley by 2 inches...it just moves 2 inches from your perspective. So the mass actually gets closer to the pulley by 1inch.
9502kayla1671 2 years ago 2
This comment has received too many negative votes show
this is a basic year 11 problem for hong kong students..
i've done this question in the easier sections of my public examination.
No wonder they say HKCEE / HKALE are the most difficult and competitive examinations in the whole world.
in fact, a C in HKALE is equal to an A in GCE...and a D can possibly be equal to an A too.
DaAfterburner 2 years ago
just too easy........try smthin harder
dhruvsporty1899 2 years ago
I wish you would make chemistry video too.
You are a good teacher because when I watch your video I understand it.
And my chemistry is bad, I wish I could understand it too.
Thank you so much for the videos. :)
sharron2792 3 years ago 14
I second this.
Paulorific 2 years ago
@sharron2792 he has a ton of normal and organic chemistry videos on his website.
username6333 2 weeks ago
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dude physics is sooo hard....i watched ur vids n still failed my physics test...college physics is nothin like ur teachin
bangalirussian 3 years ago
do u go to MIT or something?
xlwaiyiplx 2 years ago 3
this guy is a great teacher!
jayospina 3 years ago 30
ooo yea baby im a physics master....lol if i was i wouldnt watch ur vids...
bangalirussian 3 years ago
lol physics master
DeathByLight 4 years ago 7