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Dr Ben Yelverton
United Kingdom
เข้าร่วมเมื่อ 11 พ.ย. 2020
Hello! On this channel, I share educational videos about Physics & Maths. I studied at Cambridge for 8 years, first gaining an MSci in Natural Sciences (specialising in Physics) and then a PhD in Astronomy. During my PhD, I also worked as a Physics supervisor for four different Cambridge colleges. Now, I'm working as a private tutor, teaching Physics & Maths up to A Level standard. More information here: benyelverton.com/
Understanding branch cuts: f(z) = (a²-z²)^½
Gaining some understanding and intuition about branch points and branch cuts, taking as an example the function f(z) = (a²-z²)^½. We discuss how branch cuts can be used to make f(z) single-valued and show how making a branch cut is equivalent to restricting the arguments of z relative to the function's branch points. Next time we'll use these results to help evaluate a certain contour integral!
About me: I studied Physics at the University of Cambridge, then stayed on to get a PhD in Astronomy. During my PhD, I also spent four years teaching Physics undergraduates at the university. Now, I'm working as a private tutor, teaching Physics & Maths up to A Level standard.
Support the channel: ko-fi.com/benyelverton
My website: benyelverton.com/
#mathematics #complexnumbers #branchpoints #branchcuts #exponential #complexanalysis #fractionalpowers #multivalued #argument #modulus #argganddiagram #maths #math #science #education
About me: I studied Physics at the University of Cambridge, then stayed on to get a PhD in Astronomy. During my PhD, I also spent four years teaching Physics undergraduates at the university. Now, I'm working as a private tutor, teaching Physics & Maths up to A Level standard.
Support the channel: ko-fi.com/benyelverton
My website: benyelverton.com/
#mathematics #complexnumbers #branchpoints #branchcuts #exponential #complexanalysis #fractionalpowers #multivalued #argument #modulus #argganddiagram #maths #math #science #education
มุมมอง: 536
วีดีโอ
Spinning ball bouncing off a rough surface
มุมมอง 3.1Kหลายเดือนก่อน
A ball spinning at high angular velocity falls from height h onto a rough horizontal surface. It reaches a maximum height of kh during its subsequent motion as a projectile. If the coefficient of friction between the ball and the surface is μ, how far does the ball travel horizontally before its next bounce? Some similar problems: - Maximising bounce height for a ball hitting a step: th-cam.com...
Particle on a sliding wedge, using Lagrangian mechanics
มุมมอง 1.2K2 หลายเดือนก่อน
Solving for the time evolution of a particle sliding on a smooth wedge, which in turn slides on a smooth horizontal surface. We also consider some interesting limiting cases of the resulting solutions, to help gain some physical intuition! To support the channel: ko-fi.com/benyelverton About me: I studied Physics at the University of Cambridge, then stayed on to get a PhD in Astronomy. During m...
Why does pair production occur near nuclei?
มุมมอง 6392 หลายเดือนก่อน
By considering the conservation of energy and momentum, we explain why pair production can only take place when another particle - often a nucleus - is nearby. To support the channel: ko-fi.com/benyelverton About me: I studied Physics at the University of Cambridge, then stayed on to get a PhD in Astronomy. During my PhD, I also spent four years teaching Physics undergraduates at the university...
Fusion temperature: importance of quantum tunnelling
มุมมอง 1.2K2 หลายเดือนก่อน
Estimating the temperature required for nuclear fusion to occur, using two simple models, one classical and one quantum. Comparing the models shows that we need to invoke quantum tunnelling to obtain a realistic value for the temperature! To support the channel: ko-fi.com/benyelverton About me: I studied Physics at the University of Cambridge, then stayed on to get a PhD in Astronomy. During my...
Estimating the temperature of a star
มุมมอง 1.5K3 หลายเดือนก่อน
A quick energy-based method to estimate the temperature of a star given only its mass and radius. Although based on a simple model, the equation we derive shows surprisingly good agreement with the temperature of the Sun! To support the channel: ko-fi.com/benyelverton About me: I studied Physics at the University of Cambridge, then stayed on to get a PhD in Astronomy. During my PhD, I also spen...
Pressure inside a planet
มุมมอง 1.4K8 หลายเดือนก่อน
Finding the pressure inside a spherical planet as a function of radial distance from the centre, by integrating the equation of hydrostatic equilibrium. We assume a uniform density here, but the method can be generalised easily to the non-uniform case. Deriving the hydrostatic equilibrium condition: th-cam.com/video/rqE6psWXQLA/w-d-xo.html To support the channel: ko-fi.com/benyelverton About me...
Hydrostatic equilibrium: force-based derivation
มุมมอง 7998 หลายเดือนก่อน
Deriving the relationship between pressure gradient, density and gravitational field for a fluid in hydrostatic equilibrium, by considering the balance of forces acting on a small Cartesian fluid element. To support the channel: ko-fi.com/benyelverton About me: I studied Physics at the University of Cambridge, then stayed on to get a PhD in Astronomy. During my PhD, I also spent four years teac...
Fibonacci numbers and resistor networks
มุมมอง 9428 หลายเดือนก่อน
Exploring the relationship between the Fibonacci numbers and the effective resistances of ladder-like resistor networks, using recurrence relations. Full derivation of nth effective resistance: th-cam.com/video/8-Ow1KY0_0A/w-d-xo.html And the nth term of the Fibonacci sequence (note that this starts with 1, 1 instead of 1, 2, but is easily adaptable): th-cam.com/video/14pBNzI-yuw/w-d-xo.html Ab...
Finite resistor ladder: n repeating units
มุมมอง 1.1K8 หลายเดือนก่อน
Finding the effective resistance of a ladder-like resistor network with a finite number of repeating units, n. We need to solve a non-linear recurrence relation, and along the way we make use of matrix diagonalization. At the end, we take the limit as n becomes infinite and see that the golden ratio makes an appearance. Simple derivation in the case of infinite n: th-cam.com/video/7i_PGNp7i1o/w...
Infinite ladder of resistors: general case
มุมมอง 3.7K9 หลายเดือนก่อน
Deriving an expression for the effective resistance of an infinite ladder-like resistor network, in the general case where the repeating unit contains three arbitrary resistors. We finish with some special cases, and see how the golden ratio turns up in the solution. About me: I studied Physics at the University of Cambridge, then stayed on to get a PhD in Astronomy. During my PhD, I also spent...
When is angular momentum not parallel to angular velocity?
มุมมอง 2.6K9 หลายเดือนก่อน
Developing some intuition about the direction of a rigid body's angular momentum, with the aid of some examples. We focus particularly on the case when angular momentum and angular velocity are in different directions, and discuss how to understand this scenario in terms of applied torque. The discussion is purely in terms of vector cross products, without referring to the inertia tensor. The t...
Understanding surface tension in liquids
มุมมอง 2.5K9 หลายเดือนก่อน
Here we discuss two different (but equivalent) ways of understanding surface tension in liquids, in terms of both forces and energy. We finish by explaining how surface tension causes liquid droplets to take on a spherical shape in the absence of external forces. To support the channel: ko-fi.com/benyelverton About me: I studied Physics at the University of Cambridge, then stayed on to get a Ph...
Pressure required to inflate a balloon
มุมมอง 3.4K10 หลายเดือนก่อน
Why does it become easier to inflate a balloon once it grows beyond a certain size? Here we develop a simple model to find the excess pressure required to inflate the balloon to an arbitrary radius r, and use the result to gain some understanding of this effect. Deriving the equation Δp = 2γ/r: th-cam.com/video/CtUetjUX-yY/w-d-xo.html To support the channel: ko-fi.com/benyelverton About me: I s...
Laplace pressure in a bubble: derivation using forces
มุมมอง 2.2K10 หลายเดือนก่อน
By considering the balance of forces on a surface area element, we derive expressions for the excess pressure inside a spherical bubble in terms of the surface tension. We consider two different cases - a gas bubble surrounded by liquid, and a bubble surrounded by a thin liquid film floating in a gas. To support the channel: ko-fi.com/benyelverton About me: I studied Physics at the University o...
Single-slit diffraction using phasors
มุมมอง 93610 หลายเดือนก่อน
Single-slit diffraction using phasors
Double-slit interference with phasors
มุมมอง 1.4K10 หลายเดือนก่อน
Double-slit interference with phasors
Temperature of a planet with an atmosphere: the greenhouse effect
มุมมอง 73510 หลายเดือนก่อน
Temperature of a planet with an atmosphere: the greenhouse effect
Dust grain heated by a star: equilibrium temperature
มุมมอง 61010 หลายเดือนก่อน
Dust grain heated by a star: equilibrium temperature
Collision between spheres: general result
มุมมอง 1.2K11 หลายเดือนก่อน
Collision between spheres: general result
Why do particles of equal mass rebound at 90 degrees?
มุมมอง 3.7K11 หลายเดือนก่อน
Why do particles of equal mass rebound at 90 degrees?
Drag forces and the Reynolds number: intuitive understanding
มุมมอง 1.5K11 หลายเดือนก่อน
Drag forces and the Reynolds number: intuitive understanding
Why can orbital and spin angular momenta be added?
มุมมอง 2.2Kปีที่แล้ว
Why can orbital and spin angular momenta be added?
Why does Kapitza's pendulum oscillate upside down?
มุมมอง 3.6Kปีที่แล้ว
Why does Kapitza's pendulum oscillate upside down?
What is the electric displacement field?
มุมมอง 12Kปีที่แล้ว
What is the electric displacement field?
Bound charge density: why does ρ = -∇⋅P?
มุมมอง 3.3Kปีที่แล้ว
Bound charge density: why does ρ = -∇⋅P?
Polarisation and surface charge: why does σ = P⋅n?
มุมมอง 3.8Kปีที่แล้ว
Polarisation and surface charge: why does σ = P⋅n?
Angle at which particle leaves sphere: force-free method
มุมมอง 1.9Kปีที่แล้ว
Angle at which particle leaves sphere: force-free method
Ball and chain projected up a rough inclined plane
มุมมอง 1.6Kปีที่แล้ว
Ball and chain projected up a rough inclined plane
Simply marvelous ! In this solution, I've noticed that the main task was to represent R(n) as a division between P(n) and Q(n). From that, the remainder seems to be something straightforward. What was your insigth about that? Is It a common practice when dealing with recurrence relations?
amazing special cases --- Physics WORKS!
thank you Dr.!
omg thanks for your video , I've searched through so many materials about this , and honestly, this is the best video I've found.
What exactly is the difference between the natural length (l) and d? Thank you for sharing this video.
d is the spacing between the masses in their undisturbed positions, while l is the length that the springs would have if you disconnected them from the masses and removed all applied forces from them. These are not necessarily equal, since the springs may already be stretched when the masses are all sitting in equilibrium.
Finally...something regarding complex analysis...love the video....I would greatly appreciate it if you would make more videos on this topic...especially branch cuts of more complicated functions....
Excellent, I'm glad you enjoyed this!
First!
Very well presented mathematics too, thanks.
Thank you!
Don't we need to specify that the rope is massless? (that is an implicit assumption, right?) Or is there some reason that your infinitesimal free body diagram did not incorporate the gravitational force of mass?
You're right, we're just neglecting the weight!
@DrBenYelverton thank you for responding. And thank you for the video!
This seems like the opposite of alpha decay. In an alpha decay situation, there is an alpha particle trapped inside the attractive nuclear force region that eventually tunnels to the outside world.
Exactly right!
Thank you for your explanation!
Thanks for watching!
Good explaination
Thank you!
Very cool and good job, but... I'm pretty sure in the case of these high altitude ice crystals, causing halos, sun dogs etc, were considering hexagonal crystals, right? I suppose in some way its related because those can be made of, be composed of triangles, so maybe it works the same, I'm just wondering if this is the same or if the math is actually a bit different since its hexagons.
Things are slightly more complicated if you do the analysis for a hexagon, but the equilateral triangle is a pretty good model because you can turn an equilateral triangle into a hexagon by cutting the corners off!
Great 👍
Thank you. Absolutely what I wanted.
Excellent, I'm glad it helped!
Was a huge confusion before this video, now crystal clear, love from Türkiye.
Excellent, I'm glad this helped!
Hi Dr Ben, thank you for this brilliant lecture. At 4:35, would you please elaborate how to solve the arbitrary constants A and B here if really want to solve to the end? Thanks a lot!
👍
This will help me defend my PhD thesis!
Excellent! What's your thesis on?
Thank you ! Very useful
Glad to hear that!
Thank you! Could you also make a video in which you derive a formula for the stress acting on a balloon such that the express only depends on the thickness, the radius of the sphere and the material properties? If this is possible, of course
Perhaps this is what you're looking for? th-cam.com/video/2B9Yfa15uPg/w-d-xo.html
@DrBenYelverton Unfortunately, no. Let me explain the problem: starting from 0 km, the balloon ascend until it reaches the desired height. Calling dp = helium press - air press, which of the following scenarios happens? 1. dp = 0 ----> dp increases as the balloon expands, until it bursts 2. dp >0 -----> ? Then, considering the fact that the thickness reduces, how do you compute the stress? In your expression for the stress, sigma = E*(r -r0)/r0, I don't see the initial thickness and the change in the pressure variation
Would you care to explain the meaning behind the differential values? I am confused because in a math course I have never seen a differential element used on its own like this, but it is all over engineering and physics courses. I understand it is meant to represent an "infinitesimal" value, but such isn't defined in mathematics and is considered non-rigorous. I am an engineering student btw, but we were never explicitly taught how we may or may not treat infinitesimals by our lecturers. What does it actually represent in equations such as this? Should I consider it just a very small value (ie. a shorthand for a delta approaching 0)? I understand the hand-waviness behind the differentials in physics and engineering is fine as long as you are dealing with single-variable calculus, but problems will arise without proper mathematical treatment of such elements in multivariable calc. (multivariable chain rule just to name one - can't simply cancel the differentials out as if they were parts of a fraction).
Thank you very much, in A/l's we solve these kind of sliding wedge problems - through : Newtonian perspective : but trust me, Lagrangian perspective is awesome, No tedious equations or forces : i am tired of applying, the principle of, relative acceleration : in more complicated wedges, please upload more wedge problems and solve them using Lagrangian.
Will see what else I can come up with!
Thank you for this amazing video! As a high school student, your content is invaluable for my preparation for the physics olympiad. I truly appreciate it! I would also love to see a video discussing a conducting hemisphere placed on an infinite conducting plate under a uniform electric field.
Interesting suggestion..
@@nako7569 Thanks! I hope Dr. Yelverton will appreciate it!
Thanks for your kind words and I'm glad the videos have been helpful! Will put your suggestion on my to-do list.
Another beautiful video! Weel done!
Thank you!
Came across the video by chance. The clarity of your teaching is among the highest. Thank you very much and hope you will make more videos.
That's very kind, thanks! I certainly will.
Hi sir, is ut possible to prove it by using conservation of momentum?
We used conservation of momentum to get the equation u = v + w in the video.
But wouldn't this just be the force required to raise the wheel a tiny bit off the ground? That's not the force required to get it all th eway over the step, is it?
As soon as the wheel starts to climb up, the contact force at the corner starts rotating towards the vertical, hence its horizontal component decreases. So, as long as the force F is still being applied, there will be a horizontal component of the resultant force and the wheel will eventually make it over the step.
I don’t get why E inside like in the middle isn’t drawn??? It should be proportional to D-P and because like I understand D is zero inside and the E should be -P inside then? If I’m wrong please correct me and if I’m right why didn’t you draw the lines inside in the middle?
great explanation of why m+dm instead of m-dm.
Glad to hear that, that plus sign is often a source of confusion!
excellent approach, thanx Dr Ben....however i could use a little voice loudness...i was barely hearing you with the computer volume on Max....so this means i really found your video useful and interesting till the end despite my suffering lol.
Very cool
Could you discuss about optics in the upcoming videos? My test on my physics camp is about diffraction 😊
Thank you! This is the infinitesimal derivation I was looking for.
this is honestly my favourite youtube video ever. thank you so much.
That's very kind! Thanks and I'm glad you enjoyed the video.
Another problem could be to properly solve for kh, I remember doing it 2 years back, and the results surprised me. Both components of velocity after collision are independant of radius of the ball, so any problem where a ball is spinning and collides with a surface, or even not spinning and collides obliquely with a surface has to be dealt with properly by finding angular velocities after collision and taking care of rotational energy and energy loss when it is slipping against the surface during collision, NO MATTER HOW SMALL THE BALL IS. Any problem that tells you to ignore these effects by assuming the ball is small is essentially made in the wrong light. Very interesting I might say.
Interesting - solve for kh given what information?
@@DrBenYelverton As far as I remember, only h is given, coeffecient of friction mu and rotational velocity omega. I think we may also need coeffecient of restitution. It could be that I am remembering incorrectly. I will whip up my past notes and repost here.
Can someone explain to my why assuming conservation of angular momentum and assuming the ball will stop are not at odds? Surely if the ball stops it has no angular momentum about the pivot point (or any point) However the AM is clearly nonzero before contact? (I have a final tomorrow so if anyone can tell me quickly thay would be grreeat!)
We are equating the angular momentum immediately before and immediately after the moment of impact - not the angular momentum once it's come to a stop. It wouldn't be valid to say that the angular momentum is the same once the ball has climbed the step, because the weight exerts a torque on the ball during its ascent.
3:20 What about torque due Mg?
We are equating the angular momentum immediately before and immediately after the moment of impact. These two times are separated by an infinitesimally small time interval, so the change in angular momentum due to the torque produced by the weight is negligible.
@DrBenYelverton what about the torque of the friction with the ground? I feel that it will hinder the angular momentum conservation...
You can use the second law of dynamic for angular momentum i.e. dL/dt= sum of momentum of external force. The problem is equivalent in mathematical form as pendulum. In that case you should calculate the energy loss by friction and put in energy balance.
بتبرم كتيير لسانك طويل
Why can't we simply equate the rotational and translational kinetic energy prior to the collision to potential energy after?
It's very refreshing to watch these contents of yours. Thanks
Love your content .thanks for sharing ❤
You're my hero
That's very kind! I'm glad you are enjoying the videos.