Conservation of Angular Momentum
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- Опубликовано: 28 сен 2024
- 096 - Conservation of Angular Momentum
In this video Paul Andersen explains that the angular momentum of a system will be conserved as long as there is no net external torque. Both point objects and extended objects are covered along with several examples.
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"The earth will gradually stop, but thats not something we have to worry about" OK LOL
There's virtually no friction against the Earth, so it won't stop spinning for a long, long time.
because we cannt do anything about it and it will be fatal to go against the nautre earth even if somebody comeup with this bizzare idea of spinning it continously.
Bryan Zhao not true.earth is not rotating and revoluting in a free vacumm space.instead by einstein theory we assume that it is revolving around a plane .and thus planets loose their speed while revolving or rotating
Bryan Zhao not true.earth is not rotating and revoluting in a free vacumm space.instead by einstein theory we assume that it is revolving around a plane .and thus planets loose their speed while revolving or rotating
Angular momentum( particle ) --- mvr
4:45 since the inertia of the system is doubled when there is no external torque is applied, angular velocity has to halve so that the total angular momentum of the system is conserved.
0.57 since angular momentum is a vector product of the cross multiplication of two vectors(r and p), theta has to be included in the equation where theta is the counterclockwise angle from r to p
Since you're doubling the disk mass, the speed "v" will half. Great video!
The angular velocity, that is will half
OMG I LOVE HIM!!!!!!!!! You break it down so beautifully.
VERY CLEAR THANK YOU SIR
omar hijazin Ikr
Where is the answer to the disk dropped on the other disk?
Thank u so much it was a great help!!
I understood the narratives in the video (although English very bad) thank you very much
he is the greatest man present on earth
Hello Mr. Anderson, thank you for the great video. I don't seem to be finding the answer/how to work the final question. Would you be able to direct me, please?
+Natasha K. Costa 4,6rad/s
Conservation of angular momentum (L) says it will be the same as before (L = L'). So you have to calculate the first (L=Ixω = 9.2x13 = 119.6), and then you know which the second angular momentum will be (since it's conserved, it'll be still 119.6) but now you know the mass has doubled (since we put a similar disc on top) -and the I stands for Inertia = mass x how far away it is from center-, its inertia is now double as before, but momentum shouldn't have changed, so ω must have. Now we have the momentum (L' = 119.6) we already knew (since it's conserved) and double inertia (13x2), we have to find ω' (the new velocity). So if L' = I x ω, we know 119.6 = (13 x 2) x ω. In other words: ω = 119.6 / 26. So ω = 4.6
@@yosoybrunon thanks dude
great video, thank you!!
I'm confused. You mention that angular momentum will always be maintain as long as there is no net external torque but you also mention that the Earth is gradually slowing down (?) Does that mean that there's an external torque acting on our planet? I have another question: could Earth Angular momentum speed up due to an intrinsic (inside Earth) phenomenon or, if one day it does speed up, it has to be due to an external torque? regards,
Outer space isn't 100% a vacuum, so there are particles that can cause friction on Earth surface, thus slowing it down
The earth is slowing down mainly because of tidal effects caused by the moon. The moon pulls the water towards it, but as the earth keeps rotating the water tries to move against the rotation of the earth and crashes into the continents causing the earth rotation to slow down. At the same time this creates a gravitational pull on the moon that makes it go faster and further away from earth. These numbers are extremely small however (as he said in the video, no need to worry lol). A day increases by 1.8ms every 100 years, and the moon moves ~3.78cm away from the earth each year
You're better than Khan academy. Pls start doing math too. I'd hire you as my country's education minister if I could. You deserve it
I love physics
Wheres the fkin answer
lol i have a test tmmrw give me that fucking answer
Awesome
is the answer that the inertia doubles??
Amp mass doubles and becomes 26. Keep the value in formula with initial angular momentum 119.6 and the find the angular velocity decrease to 4.6(half of original)
@@wahooooh Correct
Wouldn't it just double? Since the only thing changing is mass?
The inertia? does the inertia double?
Conservation of angular momentum (L) says it will be the same as before (L = L'). So you have to calculate the first (L=Ixω = 9.2x13 = 119.6), and then you know which the second angular momentum will be (since it's conserved, it'll be still 119.6) but now you know the mass has doubled (since we put a similar disc on top) -and the I stands for Inertia = mass x how far away it is from center-, its inertia is now double as before, but momentum shouldn't have changed, so ω must have. Now we have the momentum (L' = 119.6) we already knew (since it's conserved) and double inertia (13x2), we have to find ω' (the new velocity). So if L' = I x ω, we know 119.6 = (13 x 2) x ω. In other words: ω = 119.6 / 26. So ω = 4.6 rads/s
Angular momentum is not conserved when you change the radius of the tetherball. The angular velocity increases because angular velocity is defined as velocity divided by radius so it will increase when you decrease the radius even though the velocity remains constant. If you compare the theoretical results to those actually achieved, you will find this to be true. www.baur-research.com/Physics
thanks for help me
@@srilaxmivenkateshagencies.7974 Baur Research has an agenda to discredit the scientific consensus on this topic, and is not a reliable source of information. Here are his claims put to the test:
ruclips.net/video/YGI_sWJ1Nko/видео.html
lol
Strange place to hear this but I have to say it: GIVE YOUR LIFES TO THE LORD JESUS CHRIST FOR THE REMISSION OF YOUR SINS.... Somebody who ought to see this will see it ...yes Jesus loves you this much.Amen
Here's the answer to his question because he doesn't seem to have posted it:
L = I * w_1
L = 2I * w_2 when you drop the second mass on, the moment of inertia doubles
I * w_1 = 2I * w_2 by conservation of angular momentum
w_1 = 2w_2
so
w_2 = (1/2) * w_1
that is, the angular momentum has halved
u hv a bad handwritin
L=Iw=13X9.2=119.6
L=L'
119.6=Iw=26Xw
w=119.6/26=4.6 RAD/sec
so the w decreases to half
Hi!!Why momento of inertia duplicates?Is there a formula for that?
@@sainte5 Because the problem stipulates that a second identical disc is put on top of the previous one, so if one disc has I=13 Kg m2, two of them will have a momentum of inertia of twice those 13 Km m2, or 26 Kg m2
Haha ... What about -in the absence of frictn ( one will still rotate with w where as other won't rotate)
Lmao he didn't even put it in the description
Used your comment to double check my answer, thanks lol.
These videos are so helpful. Bozeman Science if my first priority when I am searching for physics, chemistry or other educational videos. All the lecture videos are well structured and perfectly explained.
I was so confused but i got it so listen for those who are confused lol: The answer is w=4.6 so its getting slower why? bc L= L' which cant be true when we have a bigger I yknow like when you spin and you spread your arms you kinda get slower so putting more mass in the center will make you faster. idk if you get it but i tried lol. Thank you for the video its so helpful
Angular velocity should be half of previous go get constant momentum
"mass stay the same"
No due to Eistein m∝v
Huh....Uh...
0:32 yeah nothing to worry about if your 52 , what about us lol was just a joke . Love your channel Bozeman.
But an evolutionary can’t explain why we have 2
Planets and at least 6 or more moons that are spinning opposite directions 😂😂.
Only creation science makes any sense
So crazy stuff, that you don´t even bother to put up with an explanation, when the Earth is going to lose al it´s speed... Nothing to see or understand - right?
You are awesome Mr. Anderson :))))
Think of it mr. Anderson, if it moves it´s actually under some force and Earth can´t spin if it´s not under some net force! And the speed of the Earth is not constant, it speeds up when Earth is nearest to the Sun and losing speed when it´s at it´s furthest point away in the "ellipse" around the Sun!
It's called centripetal force, or the centripetal force provided here would be the force of gravity from the sun. The Earth has a tangential velocity, which is why it orbits around the Earth.
In last question angular vel. Decreases by half
it was helpful. thanks
Answer: When the second disc is dropped it increases the moment of inertia; while the angular momentum stays the same, the angular speed will decrease.
Something like 4.6
If we have a system rotating at 99.99% of the speed of light and we reduce the radius of the system to half....
Would the system break the speed of light?
I know this is hypothetical and we would need to have to use material infinitely strong and tough, but the speed would overcome the speed of light?
I think since huge amounts of kinetic energy are involved in such a situation, you'll have to take into consideration the mass-energy equivalence, I think your question can't be answered with classic mechanics solely .. If we try to use E=m*c^2 in this situation and we assume that the object has a mass of 1kg and must be going at the speed of light, it must have a Kinetic Energy of 1.5*10^16J and if we plug that in to E=m*c^2 to find how much mass it'd have lost as energy, then the result would be that m=3*10^16/1.5*10^16=2kg which means ... its mass became NEGATIVE in reaching such energy ... quite impossible, it'd be as if .. while decreasing the radius, it just transformed into energy .... but still my answer won't really do you any good ... you might want to dive deeper into physics that goes beyond classical mechanics
This is classic physics
charles galkamax
Not classic physics when objects approach light speed, you have to factor in mass energy equivalence as the guy above talked about
In regards to conservation of angular momentum, using a rotational battery to store energy in contrast to chemical, heat etc, could be aided by expanding and contracting the rotating mass, as it directly effects torque, one can build a system where the spin meets the pull of the energy coming in, so as it absorbs energy it expands and slows down ready to absorb more energy speeding up, then at night when the energy is used it keeps contracting to keep it's speed constant as energy is reabsorbed into the house, the battery ready to absorb energy again the next day. This could help solve the solar energy storage problem. Your video made the Physics clear thank you. I just wonder if the math and materials would allow a viable battery, can it be made, would it work, it would be last very long by todays battery standards, possibly.
So at 3:52 the 1.6Kg mass is moving at 3.0m/s. The string is pulled short so that at 4:37 the same 1.6Kg mass is moving at 6.0m/s. Got it. Now; assume that after 1 revolution in both of these cases the string is cut. Since Ke=1/2mv^2, I would expect the 1.6Kg mass from the short string to have 4 times the Kinetic Energy and travel 4 times as far as was the long string. That just does not seem right. Is it?
I have been searching for such a wonderful explanation.❤❤
Thank you for clearing my doubt .
Bruh
That was helpful.
By the way, anybody else from India?
And where are you from? 🤔
how do electrons have angular momentum if they are point particles with zero volume? how do they even have mass?
They have mass
@@africanosuinternwt6305 but zero volume lol infinite density?
@@fyrerayne8882 no they have a volume
@@africanosuinternwt6305 what’s their volume?
The Best Explanation 👌 sir
Really interesting video. Can you tell me how this would relate to creating speed in the golf swing because there is also centrifugal force acting on the clubhead and I'd like to understand how these two, c.o.a.m and centrifugal force work to create significant yet efficient clubhead speed.
you create club head speed with lag, when you are at your desired backswing rotation you start from the leading leg by planting the foot, the knee then your Hips begin the torque for cracking the whip. From the waist down you are the handle and the upper body all the way to the club head is the leather tip of the bullwhip
these videos are always helpful!
Since net torque is zero isnt it at rotational equilibrium and have constant angular speed??
Hmm, sir... good lesson, and one you should really think more about because had you applied what you taught in the second part of the video to the first part, you would not have include that silly ball. Why don't you try to figure out the angular momentum of just 1 lb on the earth spinning at our yearly cycle ... +63.98 lb x your body weight.... at noon, and -63.98 at midnight... so the law of momentum explains away the "false theory" of the universe. Don't believe me.... you do the math. I think that is only about a +/-5 TON cycle every 24 hrs. Please provide an explanation, I must be looking at this wrong.
Momentum is only conserved if there are no external forces acting on a system. In the system of a 1 pound mass at rest on the Earth's surface, yes, its momentum will change during the period of Earth's rotation. But we don't expect it to be conserved. It is attached to Earth, and is acted upon by a force of gravity the whole time. The force of gravity provides the centripetal acceleration for it to stay in motion with the Earth's rotation.
This nullifies a little of the Earth's gravity that we feel, but it is less than 1% of the true gravity. This just means that at the equator, your apparent weight is 0.3% less than your true weight. That's less than a single pound for most people, so it normally goes unnoticed.
Hey thanks, that really helped
:)
Thanks sir
How would you calculate something that is spiraling while spinning?
absolutely genius!
Thank you ! ✌🏻
I don't understand: if angular momentum of a body is conserved then why isn't its linear momentum conserved as well?
Intuition tells me:
decreasing the radius by a factor a 2 effectively doubles the angular velocity
*and*
the same radius/2 and angular velocity * 2 => same linear velocity (conservation of momentum)
But I'm obviously wrong. I don't understand where?
So here a the mathematical description because I'm too deep in the youtube rabbit hole, its Friday night, and I'm about to pass out. Lemme just say this, decreasing the radius by a factor of 2 increases the angular velocity by a factor of 4. Let's prove this and start by defining our governing equations.
(1) L = r x p = r * p = r * m *v (since we're assuming its all perpendicular and r * p * sin(90) = r * p * 1
(2) v = r * w
r_1 * m * v_1 = r_2 * m * v_2
and r_2 = 2r_1 -->
r_1 * m * v_1 = 2r_1 * m * v_2 (we can cancel out common terms and are left with [1] v_1 = 2v_2, which makes sense as the radius doubled)
Now lets put it in terms of w.
v_1 = r_1 * w_1
v_2 = r_2 * w_2 = 2r_1 * w_2
subsitute these into [1] and we get: r_1 * w_1 = 2(2r_1 * w_2) (now we can cancel out common terms and are left with
[2] w_1 = 4w_2
So in fact, the angular velocity decreases by a factor of 4 when the radius is doubled.
If you want to arrive at the same conclusion using the moment of inertia for a point object, I = mr^2, then its even quicker. Radius r_2 = 2r_1 here also.
L = I * w
L_1 = L_2
L_1 = m * r_1^2 * w_1 and L_2 = m * r_2^2 * w_2
substituting r_1 for r_2 gives you:
m * r_1^2 * w_1 = m * (2r_1)^2 * w_2 (cancel out common terms)
[3] w_1 = 4w_2
My example may have been slightly different from yours but I hope you understood the concept.
Thank u sir
The momentum is from the start of the solar system and the planet that hit earth
super........
This was helpful though! Thanks
Final angular velocity=3.1 rad/s
What is the answer of the question? please tell me
Conservation of angular momentum (L) says it will be the same as before (L = L'). So you have to calculate the first (L=Ixω = 9.2x13 = 119.6), and then you know which the second angular momentum will be (since it's conserved, it'll be still 119.6) but now you know the mass has doubled (since we put a similar disc on top) -and the I stands for Inertia = mass x how far away it is from center-, its inertia is now double as before, but momentum shouldn't have changed, so ω must have. Now we have the momentum (L' = 119.6) we already knew (since it's conserved) and double inertia (13x2), we have to find ω' (the new velocity). So if L' = I x ω, we know 119.6 = (13 x 2) x ω. In other words: ω = 119.6 / 26. So ω = 4.6rads/s
You have the same name as my Multivariable Calculus teaching assistant.
Intuitive
Came here from that Keanu teaches physic video
The emperror has no clothes!
Actually , the mass very slightly increases due to the speed increase .. We should always make a note of relativity .
Does mass really increase? Or is it friction from distortion of spacetime that grows? A small mass Traveling near speed of light having similar resistance to that of a super massive body not really moving.
Kinda like If you measure displacement of large body motionless in water. vs a small body travelling very fast in water. They can encounter the same displacement. So depending how you look at it You coud assume the small one is gaining mass because it is displacing more water. When all it is, is the same mass. but the faster it goes the more it water is displaced.
Given that it might take a while for spacetime to smooth out the distortion trailing the fast moving object it only appears to gain mass.
Disc will rotate with half of angular velocity!
True?
nice video ..
it was very helpful to me ...
can u leave revision notes after every video ... plz plz
Nice please make video on gravitation
The big bang breaks this law
Thanks, great video!
anyone know the answer to the last question
he left us hanging WTF
Conservation of angular momentum (L) says it will be the same as before (L = L'). So you have to calculate the first (L=Ixω = 9.2x13 = 119.6), and then you know which the second angular momentum will be (since it's conserved, it'll be still 119.6) but now you know the mass has doubled (since we put a similar disc on top) -and the I stands for Inertia = mass x how far away it is from center-, its inertia is now double as before, but momentum shouldn't have changed, so ω must have. Now we have the momentum (L' = 119.6) we already knew (since it's conserved) and double inertia (13x2), we have to find ω' (the new velocity). So if L' = I x ω, we know 119.6 = (13 x 2) x ω. In other words: ω = 119.6 / 26. So ω = 4.6 rads/s
Thank you!!
Helpful!
wow entendí super bien
very helpful
Thank you sir🙏
Why the velocity increase as the radius is reduced
03413331712 Cadetcollege because the relationship between velocity and radius is inversely proportion, so when the radius decrease the velocity increases
thank you!!
It was really useful
Thank you soo Much!!!!!!!
Great
ur the best
hi
I see
4.6 rad/sec
How ?
Where is the solution?
Conservation of angular momentum (L) says it will be the same as before (L = L'). So you have to calculate the first (L=Ixω = 9.2x13 = 119.6), and then you know which the second angular momentum will be (since it's conserved, it'll be still 119.6) but now you know the mass has doubled (since we put a similar disc on top) -and the I stands for Inertia = mass x how far away it is from center-, its inertia is now double as before, but momentum shouldn't have changed, so ω must have. Now we have the momentum (L' = 119.6) we already knew (since it's conserved) and double inertia (13x2), we have to find ω' (the new velocity). So if L' = I x ω, we know 119.6 = (13 x 2) x ω. In other words: ω = 119.6 / 26. So ω = 4.6 rads/s
@@yosoybrunon dude i posted this question 9 months ago lol I'm taking quantum mechanics the following semester lol
thanks sir...
i got answer .their is no change of angular velocity .
Im 15 and i dont know what the hell this is. When do we learn this
.
Junior year where I am from
+ABAU5 you learn this in university. leave it alone for now.
whenever you take ap physics 1
im 15 and im taking rn
In class 11
Why two planets of our solar system spins the other way around?? Venus and Uranium lol bing bang is wrong
Tulai domnie, it's Uranus...
Seems they don't and maybe you were lied to... use his lesson here. You just have to ask the right questions... Hmm, sir... good lesson, and one you should really think more about because had you applied what you taught in the second part of the video to the first part, you would not have include that silly ball. Why don't you try to figure out the angular momentum of just 1 lb on the earth spinning at our yearly cycle ... +63.98 lb x your body weight.... at noon, and -63.98 at midnight... so the law of momentum explains away the "false theory" of the universe. Don't believe me.... you do the math. I think that is only about a +/-5 TON cycle every 24 hrs. Please provide an explanation, I must be looking at this wrong.
It was helpful even though I'm not a math guy, angular momentum is just about as interesting to me as anything else in this crazy universe. Everything is made out of energy!
Sir, I would suggest to consider what happenes with angular momentum of an entity which is acting by decreasing radius in time interval delta t. I ensure you that once you add up totality of angular momentum vectors of all envolved entities, that result will be the same compared prior to the performed action. You oversimplify by ignoring the fact that angular momentum of an acting entity changes as well. Imagine your experiment setup in a vacuum of space.
Here is a demonstration that shows exactly that. It starts an attempted demonstration to discredit this, and then analyzes better controlled demonstrations that show conservation of angular momentum makes a better predictiction than conservation of kinetic energy, and why it is OK that kinetic energy increases.
ruclips.net/video/YGI_sWJ1Nko/видео.html
this reminds me of Feynman complaining about "what makes it go? energy!" coffeeandjunk.com/knowing-something/
in that this doesn't actually explain why the rotational speed changes with changing the radius, it just says "because angular momentum is conserved". But we are no wiser, we haven't actually learned why or how the speed changed by changing the radius.
BTW don't you need to apply external torque to shorten the radius?
You need to apply an external FORCE to shorten the radius, but not necessarily an external torque. You will need to apply work done by this force on the system, to reduce the radius and increase the rotation rate.
Since angular momentum is defined by the radius, it will not be conserved when you change the radius.
John Mandlbaur if the radius increases then the moment of inertia will increase resulting in a lower angular velocity, thus the angular momentum is conserved except if there's an external net torque affecting the object
Omar If the radius increases, the moment of inertia will increase, yes, because it is defined by the radius. Also, the angular velocity will decrease because the circumference increases and there is a larger distance to traverse. But the angular momentum will also increase because it is also defined by the radius and therefore will increase when the radius increases. This is the fact, science has been making a mistake.
John Mandlbaur no you dumb fuck! You said it yourself when the radius increase , the moment of inertia will increase but the angular velocity will decrease. And since the angular momentum is defined by the inertia multiplied by the angular velocity, this means that the decrease in the angular velocity and the increase in the inertia will balance each other, making angular momentum conserved. Unlessssss! There were external forces affecting on the rotating object. Moreover, the angular velocity has no influence on the displacement of the object. Go back to school you stupid fuck
Omar, please refrain from insulting me. That is called ad-hominem which is the method that less intelligent people use in an argument. I am trying to help you. You have been taught incorrectly. Angular momentum for an orbiting object is defined as momentum cross product radius. This is also the classical definition of angular momentum. When the radius changes, the angular momentum will change. As regards your argument that the increase in inertia will balance the decrease in angular velocity, you are incorrect since the inertia is a function of the square of the radius and the angular velocity is a function of the radius (not squared). School has been teaching incorrectly. Should you wish to see more information on this, please see: www.baur-research.com/Physics.
John Mandlbaur sir, do not listen to Omar, your explanation on angular momentum made sense, thank you for clarifying it.