Disk Definition and 819 Threads

  1. C

    A rotating disk with two attached masses that slide without friction

    Homework Statement A disk rotates with angular velocity w. Two masses, Ma and Mb, slide without friction in a groove passing through the cnter of the disk. They are connected by a light string of length L, and are initially held in position by a catch, with mass Ma at distance Ra from the...
  2. twoski

    Find the Volume of a Rotating Region: Washer & Disk Method

    Homework Statement Using disks or washers, find the volume of the solid obtained by rotating the region bounded by the curves y = sec(x), y = 1, x = 1, x = -1 on the x-axis. The Attempt at a Solution This should be ridiculously easy but apparently my answer is wrong?! To calculate the...
  3. A

    Using the V-K Thm to find fundamental grp of sphere union disk in R3

    Hi, I am trying to get my head around the Van Kampen Theorem, and how this could be applied to find the fundamental group of X = the union of the unit sphere S2 in R3 and the unit disk in x-y plane? I was thinking of splitting the sphere into 3 regions - two spherical caps each having open...
  4. K

    What does disk defragmenting do?

    Turns out that my HDD and SSD are badly fragmented as they have never had a defrag run on them in more than two years. So someone recommended that I run a disk defrag. What exactly does this do? Will it make my computer run faster?
  5. P

    Constant temperature distribution across the surface of a disk

    Homework Statement First of all can i say that my question is part of a bigger problem that I'm trying to solve, but for the moment I'm stuck at this bit! I'm trying to obtain a function that will return the temperature at a chosen point (r,\theta) on a disk of radius r_{0}. The...
  6. D

    Why are MACHOs in the Halo not the disk

    Hi, I was just wondering, why are we only looking for massive compact HALO objects? Can there not be such objects in the Galaxys disk, if so why? Or have simply already detected all of them, if so how?
  7. G

    Analytic mapping from disk to disk must be rational

    Let f(x) be a function which is defined in the open unit disk (|z| < 1) and is analytic there. f(z) maps the unit disk onto itself k times, meaning |f(z)| < 1 for all |z| < 1 and every point in the unit disk has k preimages under f(z). Prove that f(z) must be a rational function. Furthermore...
  8. E

    Field of a uniformly charged disk

    I have a question about the electric field of a uniformly charged disk with radius a. I'll move point by point till i reach the part i really can't get. First of all, the surface area is made of infinite number of RINGS! So, we basically integrate the charge of the rings from r="0" to r="a"...
  9. U

    Spinning conducting disk in magnetic field

    Homework Statement I'm supposed to find the time taken for the disk to slow down from ω0 to (1/2)ω0...Here's what I've done: Since on each side of the disk there is current flowing into the centre, each side experiences a force F, so the net torque on the system = 2Fa. Then I can find...
  10. M

    Electric field of a uniformly charged disk

    Hello, I am looking at an example of finding the charge of a uniform disk with a continuous charge on the surface. They go about the problem by finding the infinitesimal charge of concentric rings dq = σdA = σ(2πr dr) The part I don't understand is that they use the area as 2πr dr...
  11. F

    What is the Electric Flux through a Small Disk near a Point Charge?

    Homework Statement A small disc or radius R with surface normal ˆ k is placed a distance z from a point charge −q,( k hat pointing along the z-axis which goes through the charge and the center of the disk.) Assuming that R ≪ z, derive an expression for the electric flux ΦE passing through...
  12. I

    Finding the area of a disk divided by a parabola function.

    Homework Statement The parabola y=1/2 x^2 divides the disk x^2+y^2 <or= to 8 into two equal parts. Find the area of both parts. Homework Equations The Attempt at a Solution I have no idea of how to go about solving this. We haven't done any application problems until now and when...
  13. 5

    Calculating Friction Force on a Rotating Disk

    Homework Statement The thing that is lying on the disk(Disko), is rotating together with disko. After the rotary frequency of disko grew twice (N X 2), friction(rubbing) Force grew F=6 ( F + 6). You have to understand friction Force module at the original frequency. Homework Equations...
  14. B

    SR, Doppler effect on rotating disk

    Homework Statement taken directly from Rindler A large disc rotates at uniform angular velocity ω in inertial frame S. Two observers O1 and O2 ride on the disc at radial distances r1 and r2. They carry clocks C1 and C2 they adjust to keep with clocks time with S, i.e., they have been adjusted...
  15. N

    Can I wire a piezo disk with detectors?

    how do i wire this disk with the detectors
  16. W

    Disk, Washer, Shell Multiple Integrals

    Homework Statement Determine how many integrals are required for disk, washer, and shell method.Homework Equations x=3y^2 - 2 and x=y^2 from (-2,0) to (1,1) about x-axis.The Attempt at a Solution Since there are no breaks or abnormalities in the graph it appears that 1 integral will solve for...
  17. K

    Can a Clay Disk Survive High RPM in a Launcher?

    I began designing a clay disk launcher for when I go to a gun range and I want it to be something like this: I am having trouble sizing an electric motor since I don't have much exposure to E.Eng. The clay pigeon launcher is about 10cm by 10cm and I calculated my exit speed to be 20-35m/s...
  18. A

    Uniformly charged disk and the E field some distance Z from the center

    Homework Statement Hi, I have a problem that describes a uniformly charged disk and the electric field a distance z from the center. I have found an equation that describes the E field at any point z already. Now I have to find out how the E field decreases as z increases-- as 1/r^2...
  19. K

    Electric field at a distance from a charged disk

    A disk of radius 2.4 cm carries a uniform surface charge density of 3.1 μ C/m2. Using reasonable approximations, find the electric field on the axis at the following distances. I have used the equation E=(Q/ε0)(1/(4*pi*r2)) I also tried the equation E=(Q/2(ε0))(1-(z/(√(z2)+(r2))) Thanks...
  20. P

    What is the velocity of the mass in the lab's frame of reference?

    Hi, Homework Statement A horizontal smooth disk of radius R rotates around its axis with constant speed ω. At t=0 a mass m is thrown at speed v0 (in the lab's frame of reference) towards the center of the disk. I am asked to write down the velocity vector of the mass in the lab's frame of...
  21. G

    Formation of accretion disk / frame drag

    came across the concept of Frame dragging. i cannot find if this phenomena also aids in addition to the conversation of angular momentum the formation of an accretion disk around neutron stars/black holes. cheers
  22. N

    Solving Metal Disk Problem: Find T

    Homework Statement A uniform metal disk (M = 8.21 kg, R = 1.88 m) is free to oscillate as a physical pendulum about an axis through the edge. Find T, the period for small oscillations. Homework Equations I = mr^{2}/4 T = 2\pi √(I/mgd) The Attempt at a Solution I combined the formula...
  23. M

    Rotational Kinematics (String attached to disk)

    Homework Statement Determine the relationship between the angular acceleration of the flywheel, the downward acceleration of the block, and the radius of the ring. Known data: Mass Ring: 1.420 kg Radius Ring (Inside, then Outside): 5.10 cm, 6.325 cm Mass Disk: 1.455 kg Radius Disk...
  24. J

    About accretion disk of a binary system

    In an X-ray binary system, in which one of the two objects is black hole candidate, there are several ways to exchange mass. A paper states that" their host systems are mass-exchange binaries containing a nondegenerate star that supplies gas to the black hole via a stellar wind or via...
  25. D

    Gravitational force between disk and particle

    Homework Statement Mass M is distributed uniformly over a disk of radius a. Find the gravitational force between this disk-shaped mass and a particle with mass m located a distance x above the center of the disk. Homework Equations The problem gives the hint to use the equation found in...
  26. Saitama

    What is the moment of inertia of an inclined disk?

    Homework Statement I am trying to find the moment of inertia of a disc (let the mass be m and radius R) inclined at an angle θ to the vertical axis. (See attachment 1) Homework Equations The Attempt at a Solution I started by taking a small element of area dA. (see attachment 2) The mass of...
  27. O

    Find Forces Over a Disk - 65 Characters

    Homework Statement http://i.imgur.com/EhPmE.png The pulley(disk) has a radius R and a mass m the rope does not slip over the pulley and the pulley spins on a frictionless axle. the coefficient of kinetic friction between block A and the surface is μk. the system is released from rest and...
  28. J

    Moments of Inertia for a Cylinder and Disk

    What are they? I have some poeple telling me that for a cylinder it's I = (1/4)MR2 + (1/12)ML2 and that for a disk it's the same. Other people have told me that it's I = (1/2)MR2 for a disk and that it's the same for a cylinder. In the past I've used the former and have gotten the right answers...
  29. M

    Kinetic Energy Ratio of an Eccentric Disk

    1. Let’s say we have a solid wheel. The wheel can be modeled as a disk. Imagine that instead, the wheel is rotated at a location location 0.47R from the center of the wheel, so that the wheel rolled around a kind of loop. Essentially, the CM goes around the dashed line in the drawing. R is the...
  30. B

    Using Shell method to solve Disk method Problem

    Homework Statement Use the shell method to find the volume of the area enclosed by: y= 16-x^2 , y= 16,x=4, around y=16 Homework Equations 2\pi\int (shell height)( shell radius) The Attempt at a Solution I tried using the disk method and obtained \frac{1024}{5}*\pi but I'm...
  31. P

    Moment of inertia of disk, the easy way out?

    Homework Statement When calculating moment of inertia of a disk there is something that really bothers me. I've googled this a lot and everywhere i look they 'assume' that the Δa = Δr*2∏r, formula for rectangle, not circle: (area of circle r+Δr - area of circle r) Δa = ∏(r+Δr)^2 - ∏r^2 = ∏r^2 +...
  32. mnb96

    How to Map Points Between the Poincaré Disk and the Cartesian Plane?

    Hello, it is well-known that with stereographic projection we can obtain a 1-1 correspondence between the points of the 2d Cartesian plane (plus the point at infinity), and the points on the Riemann sphere. What is the geometrical construction that corresponds to a 1-1 mapping between the...
  33. S

    Moment of inertia spinning disk integration

    Homework Statement I want to calculate the moment of inertia of a spinning disk via integration. I'm aware of the perpedicular axis theorem, but I want to integrate. Homework Equations I = ∫r^2dm The Attempt at a Solution if I set my coordinate axis op so that the origin of the...
  34. A

    Trying to find the Tensile Pressure in a Rotating Disk

    OK, so I'm trying to build a hyper-fast rotating disk, probably of aluminum. The tensile strength is about 200MPa (note that this is a pressure, which makes sense), and I'm trying to calculate the tensile pressure throughout the disk. The point being to find out how fast I can spin the thing...
  35. C

    How to deal with f(z) that is only analytic outside the unit disk?

    Homework Statement f(z) is analytic for |z|≥1. Let C be the unit circle. Show that the integral \frac{1}{2i\pi}\int_C\frac{f(w)}{wz-z^2}dw is 0 if |z|<1, is \frac{f(z)}{z} if |z|>1 Homework Equations The Attempt at a Solution For |z|<1 case, I tried to write the integral as \frac{1}{z2\pi...
  36. V

    Angular Velocity of a Nebula Accretion Disk

    [SOLVED]Angular Velocity of a Nebula Accretion Disk [SOLVED] According to astronomy our solar system was created about 4.5 billion years ago when the nebula of an exploded supernova accreted to form a stellar mass known as our sun. They say that this "accretion disk" or mass of clumping...
  37. Drakkith

    Is This Fomalhaut's Debris Disk?

    This is my first attempt at imaging a debris disk around a star. I chose Fomalhaut because, as far as I can tell, there are no other stars visible at this time of year in the northern hemisphere with their disk's as widely separated from them as Fomalhaut. This task is rather difficult...
  38. C

    Uniformly Charged Circular Disk

    Homework Statement In what direction (using cylindrical coordinates) around a uniformly disk does the electric field NOT point? Homework Equations The directions could be r, θ, or z. The Attempt at a Solution I don't think it can point in the θ or the z direction-- either one would...
  39. H

    Calculating Charge and Electric Field Inside a Spherical Cavity

    Homework Statement A spherical charged ball of radius "a" has an empty spherical cavity, of radius b<a, at its center. There is no charge outside the ball and no sheet-charge on its outer surface. The (radial) field has given value Ea on the outer surface; inside the ball it is given as...
  40. V

    Electric field over a non-conducting disk in term of ε0

    Homework Statement A non-conducting disk with a 4-mm thickness is lying flat. It has a -4 C/m^2 surface charge on the upper surface and a surface charge on the lower surface. In terms of epsilon naught, what is the approximate field strength 1 mm above the upper surface? Homework...
  41. H

    Charged Disk Homework: Solve E&M Qs

    Homework Statement A charged disk of total charge "Q" and radius "a" lies in the xy-plane, centered at the origin. The surface-charge density distribution is nonuniform, having the surface-density, at any point inside the disk at distance "r" from the center of the form σ(r)= m x r^2 , m...
  42. D

    Electric Field Distribution of a disk

    Hi can someone help me with this problem? A thin disc of radius 60 cm has a hole its center of radius 30 cm. A total charge of 10^-3C is distributed uniformly on its surface. Find E at a point P which is 10 cm. on the central axis of this disc. What would be the acceleration of an electron...
  43. E

    Moment Of Inertia of broken disk or ring confusion

    We all know that M.I of a Uniform rigid rod about an axis perpendicular to it's length and passing through it's center is MLsquare/12.Where M is mass and L is length of the rod. If it is broken to half such that M becomes M/2 and L becomes L/2,we can't apply ML square /12 formula to it.We have...
  44. L

    Fields generated by a rotating disk

    Homework Statement We have an uniformly charged disk with total charge q, which is rotating around its axis with constant angular velocity w. Calculate electric and magnetic field in the axis and in the rotation plane. Calculate the radiated power in one cicle. Homework Equations...
  45. Q

    3D Rigid body dynamics - Rod over rotating disk

    Homework Statement A thin uniform rod is attached to an axis through its midpoint. The axis is standing on a disk rotating with constant angular speed \Omega about its symmetry axis. The rod's midpoint is located directly above the rotational axis of the disk. Let \theta denote the rod's...
  46. E

    Spinning metallic disk without magnetic field

    Hello everybody. I have to admit that I feel quite troubled since long time, actually since I read the solution of a problem that I don't understand and whose wording I immediately pass to briefly relate you. I guess that many of you have heard about the Faraday's disk, that is, a spinning...
  47. P

    How to Determine Current Density in a Spinning Copper Disk in a Magnetic Field?

    Homework Statement A cilindrical copper disk (radius R, thickness a) at time t=0 is spinning around its axis with angular speed w in a uniform magnetic field B parallel to its axis. The edge of the disk is connected to the center with a "wire" which we assume to have negligible resistance and...
  48. A

    Disk spinning with object on top, find net acceleration of object

    Homework Statement A disk begins spinning from rest with angular acceleration @ = 12 rad/s^2. A small object is on the disk a distance r = 2.0 cm from the center. What is the magnitude of the net acceleration of the object after a time t = 0.25s? (alpha) @ = 12 rad/s^2 r = 2 cm t = 0.25 s...
  49. E

    How Does a Bullet Impact the Kinetic Energy of a Rotating Disk?

    Homework Statement A bullet with 5 g of mass and a velocity of 100m/s goes through a disk that was rested initially the disk is solid and as a radius r=20cm. It's 2cm thick and as a 2kg mass that can spin with no friction in an axis that goes through the center. The bullet goes trough the...
  50. O

    Computing arc length in Poincare disk model of hyperbolic space

    I am reading Thurston's book on the Geometry and Topology of 3-manifolds, and he describes the metric in the Poincare disk model of hyperbolic space as follows: ... the following formula for the hyperbolic metric ds^2 as a function of the Euclidean metric x^2: ds^2 = \frac{4}{(1-r^2)^2} dx^2...
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