Відео

I really enjoy such kind of problems, because I can learn a lot by just solving one single problem. Thank you very much!

What if the particle was on a hemisphere instead such that the hemisphere is kept on a frictionless surface so the hemisphere would also move, so how can we approach that problem?

Thank you for the splendid explanation. Well, where would I make changes if the ball rolls AND slides too?

Can you conserve angular momentum with the force of gravity acting on the ball's center of mass a distance R away from the step edge axis of rotation, would that not count as torque? and void the conservation of angular momentum about that axis?

Very interesting video, but there is a catch: I don't agree with one approximation you are making. It is true that ω is small, but it also true that the radius of Earth is much larger than the height of the tower! It means that the centrifugal acceleration isn't negligeable at least at mid latitudes. Let's calculate the centrifugal force in function of the latitude, considering that the height of the tower is negligable compared to the radius of Earth (Re) and taking Earth as a perfect sphere. The distance from the axis of Earth |r|=Re·cos(λ), so the vector r is [0,−Re·sin(λ)·cos(λ),Re·cos²(λ)]. Plugging the vectors r and ω into the expression of the centrifugal acceleration we obtain a(centr)= −ω x (ω x r)= [0,−Re·ω² ·sin(λ)·cos(λ),Re·ω² ·cos²(λ)] Let's plug in some numbers: |ω|=7.292E-5 rad/s, Re≈6.37E6 m and let's consider the case of λ=45°, then a(centr)=[0,−0.0169, 0.0169] m/s². The x component is always 0 and the z component is much smaller than g, so it can be ignored. We are left with a negative y component, though, that accelerates the particle towards the equator. How does it compare to Coriolis acceleration? For a tower 100 m high, vz at the end of the fall is −44.3 m/s, so the x component Coriolis acceleration reaches aₓ(Cor)=−2·ω· vz · cos(λ) =0.00457 m/s², which is actually ~3.7 time smaller than the y component of the centrifugal force! If my calculations are correct, at mid latitudes, a falling particle is more deflected towards the equator by the centrifugal force than it is to the East by the Coriolis force. Notice, however, that the y component of the centrifugal force tends to 0 as we get closer to the equator, while the Corriolis force does not, so at low latitudes the latter prevails and becomes the only source of deflection at the equator.

Terrific video!! Griffiths only allow us to visualize uniform polarization (and therefore only surface bound charges). It makes perfect sense that if the polarization is changing (I.e. has a derivative) then charges “don’t cancel out” internally. I’m going to show this to a student I’m tutoring. Thank you again!!

I understand the case where the sphere is grounded. There you can set V=0 and you have clear boundary conditions for your Poisson equation. However I completely fail to understand the case where the sphere isn't grounded. What are the boundary conditions here? I thought the point was to take some image charges that yield the same boundary conditions for the Poisson equation but these conditions are nowhere mentioned. How would we know what the potential on the surface of the non-grounded conductor is in advance? Isn't this essential information that we need before we can even start using the method of images? I've breen trying to understand this for days and it's really driving me mad.

Hello Dr. Ben, an interesting hypothetical question for you, if we were to teleport a chunk of neutron star mass the size of a golf ball here on earth , would it sink down to the core of the earth, creating earthquakes as its gravitational tidal forces rip through the crust , or will it explode? If it were to explode, it would be interesting for you to make a video on it. In a sense, how do you calculate the energy of that explosion? Its a question for fun. I think the audience might enjoy it.

Hello, sir. I have a question related to the concepts in your recent video. If we take an electron-positron pair as point particles, without a definite radius, their collision doesn’t happen in a classical way, and calculating the annihilation time becomes challenging. Using Coulomb’s law and calculus, we could derive a time-to-distance relation as they accelerate towards each other. However, as they approach close distances, the velocity derived from potential approaches the speed of light, and near the Planck length, Coulomb's law breaks down due to high uncertainty, making exact calculations difficult. Could you explain how to determine the time taken for such a particle-antiparticle annihilation, addressing these relativistic and quantum aspects?

So the particle absorbs a photon then emits a virtual photon that then decays into a particle anti-particle pair? What is meant by "in the presence"? These equations are independent of distance between the pair production and particle X. The particle could just as well be in the same atom or halfway across the observable universe, but as long as it somehow receives an impulse from the pair production, conservation of momentum is satisfied. This seems suspect because you would think that these events should be causally connected. The restrictions on what X can be is extremely loose in this framework. I could substitute X with "Milky Way Galaxy" and the math would still be the same. Could X be another photon? It seems all you have shown here is that pair production cannot occur in a universe only containing a single photon if conservation of energy and momentum are to be satisfied.

Woah, I always wondered about this. Never thought I'd see an explanation on exactly this, thanks! Also, do you happen to have a video about how magnetic fields are kind of like electric fields but in a different reference frame? I heard there is a link based on special relativity but it's hard to understand.

"Why are you learning this?" A robotics enthusiast: Nothing really important (CiWS)

Oh man, what you did!

thank you

can you do about geothermal model of the earth probably? using heat equation on steady state with a core that generates heat and a mantle. is it reasonable?

How would the transmission coefficient, which shows the probability of penetration for nuclei, can be used to solve this problem?

Can you tell what force keeps the bead on the top point of equilibrium? theta=pi. thank you for this solution

Hello sir, I have read your website and found the thesis of yours on the topics the influence of planetary and stellar companion and debris disks. Quite interesting. So, could you please tell me an overview on what is this about?

Why we use this relation in band brake and rope pulley problem both while in band brake, pure slipping is there but in case of rope-pulley pure rolling is there between rope and pulley. This result is better suits for band brake(because pure slipping is there i.e maximum value of friction u×R is generated). Please help through video. Please. louuu from india.

Nice property of wave-particle duality de Broglie equation to reduce approx. d=1 fm result. I calculated static distance exactly for hydrogen atom using Casimir effect and this distance for hydrogen atom is d=0.583 fm.

Why didn’t you take into account any relativistic effect?

The quantum analysis reminds me of the Gamow theory of radioactive alpha decay, by predicting the chance of an alpha particle tunneling out of the strong nuclear potential well. Very cool!

Welcome back, many thanks!

7:32 3/2kT term is definded as KE per gas molecule , here hydrogen is diatomic so M/2mH h2 molecules ( where mH= mass of hydro. atom)

Fantastic explanation and video!!!

Been missing your videos, cool as always

More thermodynamics and statistical mechanics please!

Great to have you back!

👍🏼

👍👍

short and clear, thanks!

Very basic question, Hope you would answer me shortly. In your video at the last part you wrote f which is F/m=gt but the force of gravity being applied on the rocket changes continiously as the rocket is gradually losing mass . so how can you write F/m=g should not it be f=(m-dm)g/m??

Tnx

Hey Dr. Ben, it's great to see you back! I really enjoyed your recent video on the temperature of a star, especially after such a lon break. Your content always brings out some of the most interesting problems in physics! I was thinking, as a follow-up to this thermodynamics topic, what if you did a video exploring how temperature changes over time for an object in a completely empty vacuum? Specifically, if we consider an object with a certain initial temperature in an ideal vacuum (with no surrounding objects), how does its temperature evolve over time as it radiates heat away? I've been trying to come up with a satisfying equation for this, but it seems like Newton's law of cooling might not fully apply in this scenario. I feel like this could be a really fascinating continuation of your recent video. Also, I wanted to say that I'm deeply sorry for your loss, and I admire your resilience in continuing to share such amazing content. Looking forward to more thought-provoking problems from you!

Sir after doing some analysis using the Stefan-Boltzmann law I found out that this model suggests that the intensity released by a star is proportional to the mass of the star raised to the power of 4 ! I find that quite interesting

Great video that shows the power of estimation theory! Thanks!

brilliant! your work in this channel is priceless, thank you

Great to have you back, sir. I had previously worked with the same problem, which after solving yielded the same result. And then tried to solve it in a non-classical, relativistic way .my initial goal was to find the potential energy of the entire system using relativistic way calculating energy (Swartzchild interior solution) , which was complicated. Based on your expertise in this field, I believe working on relativistic physics in your upcoming videos will be very brilliant and intresting like this one.

Sir I have been doing a lot of physics problems some of them are very hard where can I share the problems with you?

👍🏼

Prof takes a break and then the first video he posts is calculating temperature of the star 💀

ONE QUESTION: MINUTE 8:35: WHY IS IT THAT VECTOR "r" DOES NOT HAVE Z-COMPONENT??

I think I must finish high school first (and not try to understand it in middle school 💀)

cheers m8

hello why isn't t1>t2?

Amazing❤thanksssss

IPhO 2024 T1, youre the goat for anyone whos prepping for a physics olympiad sir

Sir what if we throw the mass from the top of the incline (here, point P), will the angle change ?😊

Very elegant and simple derivation. Thanks!

Thank you sir love from india