Disc Definition and 374 Threads

Why does a body kept on a rotating disc tend to slip away from the centre?

Homework Statement A disc of radius R and mass M lays on a smooth table. a smooth channel is carved along the diameter and on both ends there are masses m. one of the masses is attached with a wire to a small, almost weightless motor that is in the center. the other mass remains fixed in place...

Homework Statement A uniform chain of length L = πR and mass M is placed on the upper half of a uniform thin disc of radius R and mass M. The disc is placed vertically and can rotate freely about its center that is fixed in space. With a small disturbance the chain starts to fall. Find out the...

I am trying to spec out a motor to move a disc on a bearing, the disc has a mass on it weighing 20,000lbs. The diameter of the disc is 3.33ft. Angular acceleration of 0.1047 rad/s^2 to 3RPM. I am assuming coefficient of friction of 0.5. 1. Can I use the assumption that the mass on the disc...

A particle is attached to an inextensible string. The other end of the string is attached to the centre of a rotating rough disc. The string is shorter than the radius of the disc so the particle remains on the disc and moves in uniform circular motion. I don't remember the quantities but the...

1. Problem: Determine the final translational speed of a spinning disc that is dropped on an infinite horizontal plane. Think of spinning up an automobile wheel suspended over a road (wheel spinning normal to the road), then dropping the wheel on the road. When the wheel rim touches the road...

Homework Statement Consider this question: "A uniform thin flat isolated disc is floating in space. It has radius R and mass m. A force F is applied to it at a distance ##d=\frac {R}{2}## from the centre of the disc. So, Will the disc rotate with accelerating in the direction of force or it...

(@mfb posted an article about this here, I think it deserves an own thread, and I did not find one, so I start one :smile:) The comet-like composition of a protoplanetary disk as revealed by complex cyanides Karin I. Öberg, Viviana V. Guzmán, Kenji Furuya, Chunhua Qi, Yuri Aikawa, Sean M...

My teacher taught us how to locate position of centre of mass in semicircular disc She said circular disc is made up of two semicircles .It's centre of mass is located in centre .But When one of the semicircles is taken out from the circle , only one semicircle is left out.To locate the...

Hello, I need to replicate the conditions of a clutch on a pin on disc tribometer to measure the coefficient of friction. However the tribometer I have access to can't spin faster than 1000 RPM. The clutch will reach speeds from 3000 RPM to 9000 RPM. I calculated the normal force required on...

Does a non rotating BH have an accretion disc?

Homework Statement Attached. Homework Equations The Attempt at a Solution For the first part I determined the net magnetic dipole moment of the disc by calculating the number of moles the iron the disc comprises of and hence the number of atoms. Then, by making the assumption that 30%...

Homework Statement A disc is on a desk, with a rotation point underneath. A string is wrapped around it, and the end of the string has a mass attached to it. The string end is put over a pulley, and when the mass is dropped it causes the disc to rotate. We are given mass of the disc (80g)...

When you put o disc on top of a plank and if you pull the plank, the disc rotates but stays stationary. Here the friction between the plank and disk produces an unbalanced torque and hence it spins.But this friction should also cause an acceleration in the disc right? Then why does it remain...

Can anyone please give m the definition of disc scalelength?

Homework Statement A man is walking at a constant velocity v along the circumference of a disc which is pivoted at a point on it's circumference. The man starts diametrically opposite to the pivot and the disc starts at rest. The man and disc have the same mass. When the man reaches back to his...

Homework Statement Calculate the electric field on axis of a disc that has charge +q on one half and -q on the other. Describe the behavior of the potential along the same axis at points far from the disc. Homework EquationsThe Attempt at a Solution My intuition says its zero, as for every...

Hi, How do you calculate the current from a faraday disc? I have found calculations for the voltage, but what about the current? I think it is a bit more complicated due to back emf, but if you know what motor you are using (the torque it can generate), then can you work it out? Thanks for any...

http://www.sciencedaily.com/releases/2014/11/141125111816.htm?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+sciencedaily%2Fmatter_energy%2Fsolar_energy+%28Solar+Energy+News+--+ScienceDaily%29 Pretty cool use of a mass produced product but how much do you think a Chuck Norris disk...

Hello everyone , as for starters I would like to ask two questions. As I've been reading about the homopolar generator I have the basic understanding of all the workings yet here are my questions. Since the rotatig disc produces a current within while rotating in an axial magnetic field...

The Faraday paradox is a hard one to get ones head around and I was wondering if there is a similar scenario, involving an E field where there is / or is not an induced emf?

Homework Statement A length of thread is wrapped many times around a steel disc of mass M and radius R, which is free to rotate around a fixed, frictionless, horizontal axle. The end of the thread is connected to a small object of mass m. If this small mass is held at rest and then released...

Hi there! I wonder where the resolution limit for a microscope comes out. I know that the lens can act as a circular aperture of diameter D and so a point source is diffracted in a disk of angular aperture 1.22\lambda/D Two sources are resolved if their distance is greater than (without Abbe...

Hi! I am creating this thread to ask what is the physical phenomena that drive the smooth disengagement of clutch discs from flywheels. I am thinking about car clutches, specifically a longitudinal front engine, rear wheel drive clutch type. I've been reading some books that describe the...

Hello, I am facing some problem with Poincare disc. (1) How to visualize a Poincare disc? (2) The arc which runs at the end cannot be reached and runs till infinity. How does it happen?

hi there, I am trying to prove the following inequality: let z\in \mathbb{D} then \left| \frac{z}{\lambda} +1-\frac{1}{\lambda}\right|<1 if and only if \lambda\geq1. The direction if \lambda>1 is pretty easy, but I am wondering about the other direction. Thanks in advance

I need to compute for the relief capacity (gpm or lb/hr) of a 10" rupture disc with relief valve set at 180psig. Vented out into the atmosphere. Assume fluid is water at 140F. I tried using ASME and API Equation but they give different answers. Can someone tell me the correct answer and what...

Homework Statement find the global extrema on the disc x^2 + y^2 \le 1 given the function f(x,y)=xy+5y The Attempt at a Solution For the interior of the disc \nabla f = <y,x+5> the critical point is (0,-5) for the boundary of the disc using lagrange multipliers...

Homework Statement If f is analytic on the closed disc, show that for r<1 we have f(re^{i\phi}) = \frac{1}{2\pi} \int_{0}^{2\pi}\frac{f(e^{i\theta})}{1-re^{i(\phi - \theta)}}d\theta Homework Equations The Attempt at a Solution I tried using cauchy integral formula and end up...

I want to show that the modulus of the automorphism \frac{a-z}{1-\overline{a}z} is strictly bounded by 1 in the unit disc. Applying Schwarz lemma gives the result immediately. But I am looking for a straight forward proof for that. Thanks in advance

Homework Statement A uniform disk of mass 2M, radius R, is mounted on a frictionless horizontal pivot through its principal axis. The disk has an additional point-mass, M, fixed to a point on its circumference. (a) Give the Lagrangian for this system. (b) Find the frequency of small...

ω = dΘ/dt if any points on a uniform disc have the same angular velocity then the corollary implies that any point on the disc must transverse 2π rad in the same amount of time. Is there a mathematical way to demostrate this or is this only demostratable purely by experiement?

This seems like it would be pretty simple and I apologize if this is in the wrong area, here goes. Picture a flat disc. It is supported by a pin or marble in the center. There are no forces acting on it. Now at 0 deg, I apply a force F (all forces are a distance equal from the center)...

Homework Statement Find the center of mass of a uniform sheet in the form of a circular disc with a hole bounded by the equations x^2 + y^2 ≤ 1 and (x - 1/2)^2 + y^2 ≥ (1/16). Homework Equations The Attempt at a Solution

I previously asked a question about this problem. I think I found the answer myself, and I want to know how I did. I'm pretty new at this proof thing and have been working through the textbook Real Mathematical Analysis by Charles Chapman Pugh. Any criticism would be appreciated! Problem...

The following problem is from the textbook "Real Mathematical Analysis" by Charles Chapman Pugh. Given ##\epsilon > 0##, show that the unit disc contains finitely many dyadic squares whose total area exceeds ##\pi - \epsilon##, and which intersect each other only along their boundaries. I...

During the time a compact disc (CD) accelerates from rest to a constant rotational speed of 477 rev/min, it rotates through an angular displacement of 0.250 rev. What is the angular acceleration of the CD? I converted 477 rev/min into 49.95 rad I converted 0.250 rev to radians which is 1.57 rad...

Homework Statement Two circular disks, each of area 4.10×10-4 m2, are situated parallel to one another. The distance between them is small compared with their radii. Both disks are uniformly charged; their charges per unit area are σ = 5.00×10-5 C/m2 for one and -σ = -5.00×10-5 C/m2 for the...

Hi, As part of an experiment I am doing I have a small uniform circular disc that is submerged in 20ml of a liquid and is spinning at 2000rpm for 60 seconds. The disc is 1mm thick and 40mm in diameter. I am trying to see what effect the spinning disc has on the growth of cells that are in the...

If I had a spoked disc made of unobtainium that could be spun up to .9999c outer rim speed, what would it look like as compared to the disc at rest? Assume I can photo the spinning wheel with an ultra fast camera.

If I have a spinning circular disc of uniform density, how would I find the torque generated by friction, if the disc is lying flat against a table with coefficient of friction μ? τ=Fxr, but what is F, and what is r in this case?

Homework Statement An insulating disc of radius a has uniform surface charge density σ and is rotating at constant angular velocity w about a perpendicular axis through it's centre. a)What is the surface current density ##\vec{j}(\underline{r})## at a position ##\underline{r}## relative to...

Homework Statement Visible light passing through a circular hole forms a diffraction disc of radius 0.1mm on a screen. If X-ray is passed through the same set up, what will happen to the radius of diffraction disc? The Attempt at a Solution I'm really clueless regarding this question. I...

Homework Statement A charge ##(5\sqrt{2}+2\sqrt{5})## coulomb is placed on the axis of an infinite disc at distance ##a## from the centre of disc. The flux of this charge on the part of the disc having inner and outer radius of ##a## and ##2a## will be A)##\dfrac{3}{2\epsilon_0}##...

Homework Statement I've to demonstrate the electric potential that a charge q feels when it's broght from infinite to a point z. The problem is that every demonstration i found out there starts with the definition of potential eletric as dV = k. dq/ r²; but i cannot use that, 'cause my...

The mass of the disc is M and the radius is R. The problem states: A disc completes 44 revolutions as it slows from an angular speed of 1.5 rad/sec to a complete stop. 1)W/ acceleration constant, what times is required for it to come to rest? 2) what is the angular acceleration...

Is the question in the paint document flawed? The question says. How many socks must he take out to be sure that he has at least two black socks? The solution to this problem is.. in case if all twelve pickings are brown... Well how can he be sure that all twelve pickings are brown? He...

A disc of radius r is spinning about its center in the horizontal plane with a constant angular speed w (omega). A bug walks along the radius of the spinning disc traveling from the center of the disc toward the edge. The bug maintains a constant speed v relative to the disc. (In other words...

Consider a charged wire with constant linear charge density λ. The wire has length 2πa and is attached to the edge of a disc with radius a. In the central region of the disc (a circular region of radius b<a) a constant magnetic field B is applied (perpendicular to the disc). The magnetic...

Here is the experiment in brief for those uninitiated : http://media.uws.ac.uk/~davison/labpage/leedisk/leedisk.html My question is, when the steady state has been obtained (heat flowing into Brass Disc = heat flowing out of it), why do we remove the upper Brass Base and then heat the disc...